Define a Computer System
A computer system is a device used for processing which often contains an input, output, processor (CPU) and storage device. More modern computer system now have the ability to communicate with each other. You may give examples of an input devices such as a keyboard
Describe the importance of computer systems in the modern world
We rely on computers more and more everyday as technology has improved. It influences many aspects of our lives including work, leisure, health and education. For instance, the traffic light systems on our roads use computer systems. Without them, we would have no traffic control, cars, busses and even auto-pilot on planes. Moreover, in health, we would not have life support and other monitoring equipment. We would not have the technology like radars and satellites to communicate with other countries and the internet. We would not be able to detect danger or threats from other countries. Other early warning systems would fail like those for hurricanes etc.
Explain the need for reliability in computer systems
Firstly reliability is: how much you can depend on the computer system being available when you use it. Usually measured in terms of availability.
So availability is the proportion of time that a system is operational usual expressed a percentage over a certain period of time. For instance, 85% in one year. Moreover, we need reliable computer systems because we rely on computers more and more everyday. Our lives often depend on computers as shown with life support and auto-pilot. We need the technology to work all the time otherwise the consequences may be disastrous and may result into death even.
Way to enforce reliability in computer systems:
Dual power supplies so if one fails, the other power supply can take over.
In case of failure, organisations need a disaster recovery plan to reduce the amount of downtime on a network for instance and to stop the reduction for profit in terms of businesses.
Regular Backups - several generations of data being backed up so we can restore them in the event of system failure or operator mistake.
RAID drives - if a hard drive fails, the data is stored on more than one drive so can be retrieved.
Uninterruptible Power Supplies - if the mains power fails, the battery can take over and shut the system without causing damage
Explain the need for adherence to suitable professional standards in the development, use and maintenance of computer systems
Every person in the team must work in the same way so everyone can understand and add on to what has been done
Computer systems are often made by a group of programmers so it is important to add commentary so that all programmers can understand what has been done and that developers understand how the code works
Moreover, systems should be thoroughly documented with user manuals to help the user understand how it works and what to do if there is a problem.
Professional standards allow programmers to do the following:
modify someone else's program
Move to a different company without needing to re-learn standards
Working in teams on the same program at the same time
Professional standards fall into four categories:
Open, proprietary, industry and de facto
Explain the importance of ethical, environmental and legal considerations when creating computer systems
The importance of ethical considerations are that:
not everyone can afford to have a computer system whereas some people can afford to have many. Lots of people wonder as to whether it is fair that only some people can enjoy the privileges of having a computer system. Some people may lose their jobs from computer systems and there are issues regarding cyber bullying for instance. Is the internet a safe place for children?
People in poorer countries may be exploited.
Some disabled people can't use computer systems
Environmental influences
There are negatives:
The production of computer uses finite and dangerous chemicals such as mercury. The making uses fossil fuels which releases pollution. They also use energy to run on. Moreover, old computers are not easy to dispose of and are not always recycled as they should be resulting in more waste going into landfills, including the toxic components. CS sometimes use scarce natural resources.
There are benefits:
You can work at home which means less fossil fuels from travelling to work. Another advantage is that you are bound to use less paper which means less trees will be cut (communication sent electronically so no waste of paper and ink). Industrial processes that are computer-controlled rather than overseen only by a human are more efficient and therefore less polluting.
Legalities
Computer systems must conform to the law by several measures such as:
Define the term of hardware
The physical components of a computer systems such as a keyboard, mouse, projector and monitor
State the purpose of the CPU
It is a device used for processing and conducting the fetch and execute cycle precisely by fetching, decoding and executing instructions fetched by the RAM from the secondary storage.
Describe the function of the CPU as fetching and executing instructions in memory
The RAM (Random Access Memory) of the CPU fetches instructions from the secondary memory of the computer like the hard disk and transfers the instructions to the cache memory which transfers the instruction to the CPU. The processor decodes the instructions and executes them. There are two main components of the CPU.
The Arithmetic Logic Unit carries out calculations as well as similar numeric functions such as comparing which two numbers are larger
The Control Unit is responsible for retrieving data and instructions from the correct location in the memory and executing those instructions. This might involve calling on other pieces of hardware like the ALU.
Explain how common characteristics of CPUs such as clock speed, cache size and number of cores affect their performance?
Clock Speed
The higher the clock speed, the faster the CPU
It represents the number of instructions the CPU can process per second
Cache Size
The more cache in the CPU, the less time is spent accessing memory. It contains frequently accessed data.
The number of independent processors within the CPU
More instructions can be executed simultaneously
Explain why data is represented in computer systems in binary form
Data is represented in binary form because computers work by switching electrical signals on and off. Computer components soften have two states that can easily model 0 and 1 too, like a magnet on a hard disk can be aligned to either north or south and a circuit can be either open or closed. Secondly, binary is high tolerance so it is unlikely that a computer could mistake a 0 for a 1.
Describe the difference between RAM and ROM
RAM is a volatile form of memory meaning it will lose all of its contents once the computer system is switched off. However, ROM is a long-term non-volatile form of memory meaning the content won't be lost even with the power off.
RAM stores currently used programs whereas the ROM stores the operating system and the bootstrapper which tells the computer how to initialise the operating system when the computer turns on.
The contents of the RAM can be changed but the content of the ROM can not be changed.
Explain the need for ROM in a computer system
When a computer system starts, it must have some instructions to follow so that the computer is correctly set up. The program is called BIOS (Basic Input Output System) and the bootstrapping instructions. The BIOS is stored in the ROM because the content needs to remain and stay there when there is no power.
Describe the purpose of RAM in a computer system
A computer system needs to store programs and data when it is running. The speed of the computer system will be limited by the speed of this storage RAM is used because it offers a good compromise between cost and speed. It also fetches instructions and transmits them to the cache memory thus to the CPU so it works in the fetch and execute cycle.
Explain how the amount of RAM in a personal computer affects the performance of the computer
The more RAM there is, the more programs can be running simultaneously.
OR: As operating systems systems on desktop computers get more and more complex, they need to use larger and larger amounts of storage to run their programs. Adding more RAM means that the data doesn't need to be swapped as often so the system will run faster.
Explain the need for virtual memory
If RAM is not large enough to store all of the data and instructions that it is required to store, virtual memory may be used. This is when the hard disk is used as an extension of the RAM and temporary gives memory addresses as if it were RAM. This technique can be done by modern operating systems.
Describe cache memory
Cache memory is a high-speed store of frequently used programs by the processor of the CPU. It stories copies of data or instructions from the RAM. It has the fastest access speed for memory and will usually be small. It is expensive.
Describe flash memory
Flash memory uses electronic chips as storage. It is non-volatile and is a portable, solid-state memory technology. Examples of flash memory are USB drives which are frequently used to transfer data between computer systems and memory cards. Memory cards can also be used by computer systems but they are more commonly used to provide storage in devices such as digital cameras and to expand the storage capacity of tablet computers. Flash memory can be erased and re-programmed. Mini SD cards also use flash memory often found in mobile phones.
Discuss how changes in memory technologies are leading to innovative computer designs
Many modern computers use flash memory for the ROM which allows the contents to be updated using 'flashing'. Moreover, memory technology is getting faster, cheaper and smaller. Therefore, we get faster, cheaper and smaller devices such as tablet PCs, smart phones and larger USB pen drives.
Understand the need for input and output devices
Computers only work with digital information. Any input that a computer receives must be digitised as computers can only understand two states: on or off thus 0 and 1. The digital signals only have two states 0 and 1 like binary and the computer can only understand instructions in binary. Often, data has to be converted back to an analogue format when it's output. Output devices are needed to produce a form/display that is understandable to the user whereas input devices are used to enter data onto the computer which it can understand (binary).
Describe suitable input devices for a wide range of computer controlled situations
MAINSTREAM
MOUSE: Use to move a cursor and select icons on a GUI.
Advantages: Excellent option for users on desktop computers and appropriate users in seated position.
Disadvantage: need a flat clean surface.
KEYBOARD: Use to enter text and numbers into a computer system.
Advantage is that it is a reliable form of data entry so an A will only mean an A
Disadvantage is it is slow to enter text/numbers. The user is very prone to errors and is not good for users with poor dexterity (poor finger control).
SPECIALIST
TOUCH SCREEN: users can drag, select, expand items without an additional device. It is very intuitive and no additional devices are required. A disadvantage is that is does not work if fingers are went or if the user is wearing gloves.
SENSORS: Used to capture the movement of the user. An advantage is that the user can control a computer system without contact with a device. Disadvantage is that the gestures can be misinterpreted by the system and they often require light.
OMR (Optical Mark Recognition) Scanners are devices which recognises marks on a document which correspond to data. They are often used in surveys/multiple choice questions.
Barcode Scanner: Scans the widths of the lines and spaces. These widths represent a unique code. When the code is captured by the scanner, the code is looked up in a database and the item information is displayed.
RFID (Radio Frequency Identification) - Tags are placed on items and the tags themselves stores data/unique code like a bar code. Unlike a bar code, these tags don't need to be in line of sight of the scanner. The scanner sends a signal to the tag and receives a response which is the code.
Describe suitable output devices for a wide range of computer controlled situations
Monitor: Displays information via pixels on a screen. Pixels continue to present us with languages that we can recognise and gain information from. Used in a wide range of areas like home and office. It usually accompanies with a desktop computer.
Projector: presents an image on a screen/wall/object which we recognise and can gain information from. It is used in cinemas, schools, video conferencing etc.
Printer.
SPECIALIST/INDUSTRY OUTPUT DEVICES
Actuators: these are output devices which produce movement/motion. For example they are used to control the flaps on the wing of the plane to drop if the autopilot senses an increase or decrease in altitude.
Plotter: It is a specialist output device which prints huge images onto massive sheets of paper. They are used to create technical drawings or blueprints.
Discuss input and output devices for users with specific needs
INPUT DEVICES
Such-puff-switch: Paralysed users can use their mouth to control a switch. Programs can interpret these inputs to carry out a number of tasks.
Eye-Tracker: Cameras locate the eye and the direction that the person is looking. The cursor will follow the eye movement. Staring at an icon will select it.
Foot Mouse: Users with limited arm movement can use their feet to control and select icons.
Braille keyboard: Users with poor sight can use two types of keyboards: normal keyboard with braille to guide them to the correct letter or a keyboard which the user can select the position of the dots to create each braille letter.
OUTPUT DEVICES
Braille printer: These work by punching holes or raising them using software, to form the Braille that someone who is visually impaired can feel and interpret as information thus understand.
Voice Synthesis: These output devices which is a speaker and screen combined allow users who cannot naturally communicate to pick letters and words from a screen. The synthesiser will then synthesise human speech to speak the letters/words aloud.
Screen Magnification: Screen magnification software will adapt the screen so that partially sighted people can more easily read the information on the screen.
Screen Reader: Like the screen magnification software, this adapts the output device (screen) to present the text in a 'spoken' form.
Explain the need for secondary storage
Secondary storage is needed because it is non-volatile so it won't lose its content when the computer is turned off. Therefore, the secondary storage devices can save all the data in its original form. This is needed for two main reasons: The computer's working memory is finite and limited in size so it cannot always hold the data we need.
Also, remember that secondary storage refers to storage devices and media that are not constantly accessible by the computer system like CDS, portable flash frives, external had drives etc.
Describe common storage technologies such as optical, magnetic and solid state
OPTICAL storage media, including CDs, DVDs and Blu-Ray disks are written to and read from using lasers. Optical disks spin to allow the laser to read the data from the correct location. The surface of the disk will have billions of locations in which holes can be physically burned by a laser or not burned which can represent either 0 or 1 thus binary instructions.
MAGNETIC storage devices: the disk will spin at a high speed under the read/write heads which is symbolic of the north and south poles thus 0 or 1 states of binary instructions.
SOLID STATES: have no moving parts and all storage technologies including solid states are non-volatile. Solid state uses electronic circuits. These devices are both sturdier and quieter than magnetic or optical devices.
Select suitable storage devices and storage media for a given application and justify their choice using characteristics such as capacity, speed, portability, durability and reliability.
SOLID STATE like usb pen drives:
Capacity - typically range from 1GB to 64GB, but higher capacities are always being developed.
Speed - could be around 5 million bits per second,
Portability- very small and light so it is designed to be moved between computers.
Durability - very durable and strong.
Solid state devices are useful for people who do not always work at the same computer but always need access to their work.
OPTICAL DISKS
Capacity - CDs: 700MB DVDS: 4.7 GB and Blu-Ray disks - 25GB
Speed - highly variable although Blue-Ray drives are much quicker than DVDs or CDs
Portability - small and light but not as easy to carry as a USB flash drive.
It is also compatible with several devices.
Durability - quite sturdy although if the surface is scratched the data can be irretrievable.
MAGNETIC like an internal hard disk drive
It is cheap
Capacity is very large, like terabytes.
Speed - data transfer from an internal drive is usually far quicker than any external device.
Portability - it is difficult and time-consuming to move an internal drive from one machine to another
Durability - very well protected inside the computer and protected by a metal case when removed.
Explain the need for the following functions of an operating system:
User interface: communication between computers and the user. An interface makes computers user-friendly.
Memory management: one of the main functions of the operating system - managing multiple applications using the space in main memory so all programs can be executed efficiently.
Peripheral management: one of the main functions of the operating system: managing the input and output of the CPU.
Multi-tasking: one of the main functions of the operating system: managing how several programs which are all running at the same time, share the processor.
Security: one of the main functions of the operating system - protecting the computer system from various hazards such as unauthorized users, viruses, hackers and accidental damage.
Describe the purpose and use of common utility programs for computer security
Anti virus: capability to guard against malicious software and it is a utility software which prevents harmful programs being installed and important files from being changed. If a virus does enter the network or computer, the anti virus software detects it and removes it. A virus is a program that is installed on a computer without your knowledge or permission and with the purpose of doing harm. It includes instructions to replicate automatically on a computer and between computers.
firewall: to protect against both software and remote hackers.
Password facilities: different users have their own usernames and passwords and only be allowed access to things they need to access.
Spyware protection stops unauthorized users from accessing the user's actions on their computer system and watching what they do without the user's permission (so they can not access the user's history for instance).
Disk organisation
An operating system is responsible for making sure files are stored in a hierarchical structure.
Operating systems also provide the user with means by which to locate files. If files are stored in a hierarchical structure, they are quicker to be searched through and can be found easier if the user is looking through each sub directory manually.
The top level of the hierarchy is called the root directory, beneath which are sub directories
Moreover, defragmentation. It is a utility program that optimises the use of the hard disk space by grouping together the separate parts of each file in one location on the disk as well as grouping together the space so newly saved files do not have to be fragmented (split up). It also quickens the time it takes to access files.
File transfer: the operating system is also responsible for moving files, both physically and physically on the disk and conceptually within the direct structure. An operating system will also be capable of moving a file from one device such as an internal hard drive to another such as a USB flash drive.
Disk formatting: formatting a disk means permanently deletes everything from it and making it ready to have new files saved to it. This process is managed by the operating system although the operating system itself is on the disk being formatted. It guarantees that viruses and other malware are removed. If a disk is going to be disposed of, it ensures all personal data is deleted. Sometimes, a disk is formatted as part of the process of installing a new operating system.
System maintenance
System information and diagnosis utilities prove information to the user and any other software about the computer, such as the hard disk capacity, processor speed and the name of the operating system.
System cleanup tools are essential along with regular fragmentation to keep a computer operating efficiently. Files that are no longer needed can be deleted.
Automatic updating ensures that a computer always has the most up-to-date version of a program available. Newer versions of programs might run quicker have more features and have better security or bugs removed. This utility is found more and more often in mobile phones as well as computers.
Discuss the relative merits of custom written, off the shelf, open source and proprietary software
Custom written software is produced specifically for you. It is expensive and takes a great deal of time to use the software. Moreover, the software is designed by the developer specifically for the purpose of the user's request.
Off-the-shelf software which is also proprietary software is the kind that you buy from a shop or pay to download it. It is quick to access and the errors are easy to fix through online forums and user manuals, unlike custom written software. It is cheaper although there is a possibility that it may not do everything you want it to do.
Open source software gives you access to the source code and allows you to make changes to customize to meet your exact needs. It is free although you would need a high level programming skill to be able to customize it.
Moreover, proprietary software is software that legally remains the property of the organisation, group or individual who created it, They do not release the code but insist only those who have bought the special license can access the program. The source code is not often sold but remains with the administrators of the computer.
The advantages are that it gives software developers an incentive to produce quality software because the developer is looking for profit. However it costs and the license does not allow the user to modify the software or to figure out how the software was made,
Define the terms bit, nibble, byte, kilobyte, megabyte, gigabyte and terabyte
Bit - 0 or 1 binary digit.
Byte - 8 bits or two nibbles
Kilobyte - 1024 bytes
Megabyte - 1024 kilobytes
Gigabyte - 1024 - megabytes
Terabyte - 1024 gigabytes
Understand that data needs to be converted into a binary format to be processed by a computer
Computers work by processing electrical signals
Electrical signals can be either on or off
Text, images, sound and instructions all need to be converted into binary so that computers can understand the information. Rows of binary are symbolic of instructions.
Explain overflow
When the result of a numeric calculation s too large to be stored in the space reserved for that type of data. What happens when overflow occurs? The user will see an error message saying 'overflow' has occurred and the computer may ignore the ninth bit,
Explain the use of binary codes to represent characters
A database will store the binary instructions for each letter. Computers can only understand binary so each binary instructions of O and 1 can equivocate to letters so the computer can understand the user's entry. A standard set of numbers used to represent each letter would mean that is is compatible between different devices
Explain the term character set
Character set is the group of symbols, letters, commands on a computer which is represented by a computer. Each character is assigned to a binary instruction. So, it is an agreed standard for how and which numbers represent each character.
Describe with examples (for ASCII and Unicode) the relationship between the number of bits per character in a character set and the number of characters which can be represented
ASCII
American Standard Code of Information Interchange
7/8 bits
256 possible values - extended ACII
normally 128 possible values.
However, originally it was worth 7 bytes and had 128 values,
It is enough to represent the whole of the English language but was not representative of other languages and accents for instance.
Unicode
It can store many more characters
16 bytes
Can cover several languages
Do two to the power of 16 to get the possible values.
Explain the representation of an image as a series of pixels represented in binary
An image is divided into pixels, each of which is a tony dot on the screen. A pixel is short for picture element. It is the smallest component of a bit-map image. A pixel can only be one color at a time, and when the picture is saved, the colour of each pixel must be stored in binary, When there more bits that are used to store each pixel, the more colours are potentially available.
Explain the need for metadata to be included in the file such as height, width and color depth
The metadata is needed in order to load the image, while date and time are helpful in making image files on a disk more searchable
Discuss the effect of color depth and resolution on the size of sound file and quality of its playback
Color depth - the number of bits used to represent the colour of a single pixel in a bit-mapped image. Higher colour depth gives a broader range of distinct colour. When more colours are needed, more bits are needed. Many images store 24 bits therefore three bytes for each colour. The more variety in the pixel, the greater the colour depth - like a certain shade of blue will use more pixels than the normal colour blue, assumed by the computer.
If we double the resolution of an image, we quadruple the amount of data that is needed to store the image because: 16 pixels wide
16 pixels high
2colours
16x16x1 bit = bits 256 (32 bytes). The resolution of an image means the number of pixels in an image expressed as the number of pixels across x the number of pixels down.
Explain how sound can be sampled and stored in digital form
Sound is a pressure wave in the air. It is continually changing which we call an analogue signal. To record the sound on a computer, we need to convert the analogue sound into numbers (digital). You may use an analogue to digital converter which can be found using the input device: microphone.
Explain how sampling intervals and other considerations affect the size of a sound file and quality of its playback
The term sample rate or sample interval are the same. They both are the time gab between measurements of the sound wave being taken. Within the sample interval, the computer includes the volume and frequency of the sound and records the sound wave multiple times per second.
A higher sampling rate results in better sound quality but requires more storage space.
Bit rate
It is how many bits are used for each sample (measured in bits per second) and this can vary widely. Again, higher bit rates result in higher quality of sound but also higher storage requirements.
So, overall. To improve the quality of the recorded sound, we can sample the sound more frequently. If you double the recording interval, the double amount of data is stored or the audio file. Additionally, we use a greater number of bits to record the sound more accurately which results in a higher resolutions.
Explain how instructions are coded as patterns
The computer can only understand binary which are single digits of 0s and 1s. Therefore, patterns of 0s and 1s are used to create instructions with the computer can understand and process. The OS will have a table of instructions which may be entered as words but the string of words may be assigned to a binary value.
Explain how the computer distinguishes between instructions and data
Every computer program is made up of instructions and data. The instructions tell the computer what to do and the data might be text, number, image or sound that the instructions are applied to. Both instructions and data will consist of a sequence of 0s and 1s. The computer needs a way to distinguish between them so each instruction and each piece of data will be stored in a specific location on the disk with a specific memory address. The OS keeps track of which memory addresses contain instructions and which contain data.
Describe a database as a persistent organised store of data
A database is a persistent, organised collection of related data.
Persistent ----> Non-volatile, stored on secondary storage such as a hard drive, more than one person can access the database at once.
Organised-----> Has "records". Can be searched, modified and deleted.
Store of Data------> Its stored and data can be anything pictures, text and music.
Explain the use of data handling software to create, maintain and interrogate a database
The use of handling data software such as a DBMS creates, maintains and interrogates a database. For instance, create means to set up the structure of the database such as tables and forms. Maintain means to update the database, edit records, add records and delete records. Interrogate means to search for data that matches certain criteria. These qualities of a data handling software are useful because they ensure data integrity, efficiency and persistence.
Moreover, storing data in a database is advantageous because data can be accessed speedily and manipulated to form new data. A single database can be shared. Moreover, data validation can take place which ensures the data is integral.
Describe how a DBMS allows the separation of data from applications and why this is desirable
DBMS stands for database management system.
This means that actual data is stored separately using the tools to view, edit and upgrade the data. Keeping the data and the program separate is a good thing because the program could be updated or even replaced with a new program and the data would not need to change. Similarly, if the data needs to change at any time, the program does not need to be altered in anyway.
Furthermore, a DBMS is a piece of software that sits between an application (the program the user works with) and this file system (the data itself).
This, therefore avoids data redundancy as all the data from one table is not copied into the other. So if one table is updated, all the data in other tables containing data from that updated table, will also have the data updated. No data will be left behind and become redundant.
Switches - Are more sophisticated than hubs as they control which data packets are being sent to each node and allow packet switching so packets of data being transmitted to other nodes on the network.
Algorithms are a series of steps to solve a problem. Can be expressed in structured English, pseudocode or as a system flowchart.
Algorithms solve problems on a computer.
Explain the difference between high level code and machine code
High level code is written in a which which humans can understand. Programming languages are high level code. A CPU can not use a high level language so it needs to be translated into machine code which is the only language the computer can understand. High level uses words. The code is designed to be read by human programmers. High level code is also portable and can be translated for different machine.
They resemble natural language.
Examples: Java, Visual Basic, Python, C#
Either an interpreter or compiler is needed to translate the code into machine code so that the computer can run it.
----------
LOW LEVEL :
Machine code is the binary that the CPU decode and executes when it runs the programs. Machine code is specific to a particular machine.
It is more difficult to understand but can often be executed by computers very quickly.
Examples: Machine code and assembly language
Machine code does not need to be translated as it is machine ready.
Assembly language requires an assembler.
Run-time environment: Allows you to run your program as you are creating it, by pressing 'play' button or equivalent.
Translators: form part of the IDE.
Auto-documentation features include automatically creating parts of the maintenance documentation for your program as you type code.
Understand and use sequence in an algorithm
When instructions are executed one after another in series without conditions.
Understand and use selection in an algorithm (IF and CASE) statements)
When the program will execute certain instructions based on conditions. Selection statements include IF.. THEN.. ELSE and CASE... OF to select which commands to execute.
CASE MenuChoice OF - This will compare a value
1: OUTPUT "Menu Choice 1"-if it's "1", this will happen...
2: OUTPUT Menu Choice 2"
3:OUTPUT Menu Choice 3"
END CASE
In terms of normal if statements, you can do the normal, IF THEN ELSE ENDIF..
Understand and use iteration in an algorithm (FOR, WHILE and REPEAT loops)
Where a program will execute a group of instructions zero or more times based on a condition. FOR loops will execute instructions a specific number of times, REPEAT... UNTIL loops for one or more times and WHILE... DO loops for zero or more time.
REPEAT
name = ..
passwords = userinput
UNTIL password=correct
The test is done at the end.
WHILE COUNT... DO ###count is a number
OUTPUT..
COUNT...It is important that whatever you are testing will be changed in this block, otherwise your loop will iterate forever.
END WHILE
FOR Count = 1 to 10 DO
OUTPUT
OUTPUT COUNT
Define the terms variable and constant as used in an imperative language
The value of a constant is set when the constant is declared
The value of a variable is set while the program is running
The value of a constant cannot be changed once the program is running/can only be set at design time A variable has no value at design time.
A value that does not change (while the program is running)
A location in memory to store / a value that may change (as the program is running)
Those answers were from the mark schemes.
A constant also refers to data that is stored in the computers memory..
Describe the data types integer, real, Boolean, character and string
Integer is a data type for whole numbers. It is often stored in memory by splitting up the binary number into 8 bits.
Real number is a data type for fractional numbers, typically 4 bytes.
Boolean is a true or false value, typically 1 bit.
A character is a single letter, number or punctuation mark, space etc. It requires one byte. Examples of character data might include 'M' or 'F' to represent gender.
String is the data type for text, more than one character. It takes up 1 byte of character.
Perform common operations on numeric and Boolean data
There are two other common operations that we can perform on numeric data:
DIV - integer division - same as a normal divide but forget part of the answer after the decimal.
MOD - Modulo calculates the remainder, as a whole number.
These two operations can be performed on real and integer numbers but both given integer answers.
Use one-dimensional arrays
An array is a group of data items of the same data type that uses a single identifier. Individual data items are accessed using a subscript.
The index values for arrays start at zero.
Arrays can be one-dimensional, in which case each element is accessed by a single number.
Describe syntax errors and logic errors which may occur while developing a program
Syntax error: an error in the format of the program statements such as missing semicolons or keywords spelt incorrectly. You can also say a syntax error are when the rules of the language have not been followed. If the code is erroneous, it will either not compile, or it wish crash when the line of error is reached.
Logic error: an error in the algorithm that means the outcome is not as expected, even though the program will run.
Select and justify test data for a program, stating the expected outcome of each test
Type of test datas: typical, extreme and invalid entries. Before a program is tested, a testing table is usually drawn up which contains the following headings:
test descriptions, test data, expected outcome, actual outcome.
Sources are from ZigZag education, OCR and Riddlesdown.org :)
A computer system is a device used for processing which often contains an input, output, processor (CPU) and storage device. More modern computer system now have the ability to communicate with each other. You may give examples of an input devices such as a keyboard
Describe the importance of computer systems in the modern world
We rely on computers more and more everyday as technology has improved. It influences many aspects of our lives including work, leisure, health and education. For instance, the traffic light systems on our roads use computer systems. Without them, we would have no traffic control, cars, busses and even auto-pilot on planes. Moreover, in health, we would not have life support and other monitoring equipment. We would not have the technology like radars and satellites to communicate with other countries and the internet. We would not be able to detect danger or threats from other countries. Other early warning systems would fail like those for hurricanes etc.
Explain the need for reliability in computer systems
Firstly reliability is: how much you can depend on the computer system being available when you use it. Usually measured in terms of availability.
So availability is the proportion of time that a system is operational usual expressed a percentage over a certain period of time. For instance, 85% in one year. Moreover, we need reliable computer systems because we rely on computers more and more everyday. Our lives often depend on computers as shown with life support and auto-pilot. We need the technology to work all the time otherwise the consequences may be disastrous and may result into death even.
Way to enforce reliability in computer systems:
Dual power supplies so if one fails, the other power supply can take over.
In case of failure, organisations need a disaster recovery plan to reduce the amount of downtime on a network for instance and to stop the reduction for profit in terms of businesses.
Regular Backups - several generations of data being backed up so we can restore them in the event of system failure or operator mistake.
RAID drives - if a hard drive fails, the data is stored on more than one drive so can be retrieved.
Uninterruptible Power Supplies - if the mains power fails, the battery can take over and shut the system without causing damage
Explain the need for adherence to suitable professional standards in the development, use and maintenance of computer systems
Every person in the team must work in the same way so everyone can understand and add on to what has been done
Computer systems are often made by a group of programmers so it is important to add commentary so that all programmers can understand what has been done and that developers understand how the code works
Moreover, systems should be thoroughly documented with user manuals to help the user understand how it works and what to do if there is a problem.
Professional standards allow programmers to do the following:
modify someone else's program
Move to a different company without needing to re-learn standards
Working in teams on the same program at the same time
Professional standards fall into four categories:
Open, proprietary, industry and de facto
Explain the importance of ethical, environmental and legal considerations when creating computer systems
The importance of ethical considerations are that:
not everyone can afford to have a computer system whereas some people can afford to have many. Lots of people wonder as to whether it is fair that only some people can enjoy the privileges of having a computer system. Some people may lose their jobs from computer systems and there are issues regarding cyber bullying for instance. Is the internet a safe place for children?
People in poorer countries may be exploited.
Some disabled people can't use computer systems
Environmental influences
There are negatives:
The production of computer uses finite and dangerous chemicals such as mercury. The making uses fossil fuels which releases pollution. They also use energy to run on. Moreover, old computers are not easy to dispose of and are not always recycled as they should be resulting in more waste going into landfills, including the toxic components. CS sometimes use scarce natural resources.
There are benefits:
You can work at home which means less fossil fuels from travelling to work. Another advantage is that you are bound to use less paper which means less trees will be cut (communication sent electronically so no waste of paper and ink). Industrial processes that are computer-controlled rather than overseen only by a human are more efficient and therefore less polluting.
Legalities
Computer systems must conform to the law by several measures such as:
- Computer Misuse Act which makes hacking illegal as it illegally gains access to another computer, perhaps by stealing a password.
- Data Protection Act makes it illegal to misuse someone's personal information. You must make sure that the data is updated and correct, only used for the intended purpose and does not share it to other people. It ensures users are entitled to their privacy. Therefore, the act gives people the right to protect their personal information on a computer system.
- Healthy and Safety at Work Act which means employers must make sure their CS are safe and do not injure their workers so cables must not be a tripping hazard.
- Too much time spent at a computer can can repetitive strain injuries from typing or using a mouse for instance.
- A poorly positioned chair which can cause back problems is forbidden.
- A monitor not at eye level can cause neck problems.
Define the term of hardware
The physical components of a computer systems such as a keyboard, mouse, projector and monitor
State the purpose of the CPU
It is a device used for processing and conducting the fetch and execute cycle precisely by fetching, decoding and executing instructions fetched by the RAM from the secondary storage.
Describe the function of the CPU as fetching and executing instructions in memory
The RAM (Random Access Memory) of the CPU fetches instructions from the secondary memory of the computer like the hard disk and transfers the instructions to the cache memory which transfers the instruction to the CPU. The processor decodes the instructions and executes them. There are two main components of the CPU.
The Arithmetic Logic Unit carries out calculations as well as similar numeric functions such as comparing which two numbers are larger
The Control Unit is responsible for retrieving data and instructions from the correct location in the memory and executing those instructions. This might involve calling on other pieces of hardware like the ALU.
Explain how common characteristics of CPUs such as clock speed, cache size and number of cores affect their performance?
Clock Speed
The higher the clock speed, the faster the CPU
It represents the number of instructions the CPU can process per second
Cache Size
The more cache in the CPU, the less time is spent accessing memory. It contains frequently accessed data.
The number of independent processors within the CPU
More instructions can be executed simultaneously
Explain why data is represented in computer systems in binary form
Data is represented in binary form because computers work by switching electrical signals on and off. Computer components soften have two states that can easily model 0 and 1 too, like a magnet on a hard disk can be aligned to either north or south and a circuit can be either open or closed. Secondly, binary is high tolerance so it is unlikely that a computer could mistake a 0 for a 1.
Describe the difference between RAM and ROM
RAM is a volatile form of memory meaning it will lose all of its contents once the computer system is switched off. However, ROM is a long-term non-volatile form of memory meaning the content won't be lost even with the power off.
RAM stores currently used programs whereas the ROM stores the operating system and the bootstrapper which tells the computer how to initialise the operating system when the computer turns on.
The contents of the RAM can be changed but the content of the ROM can not be changed.
Explain the need for ROM in a computer system
When a computer system starts, it must have some instructions to follow so that the computer is correctly set up. The program is called BIOS (Basic Input Output System) and the bootstrapping instructions. The BIOS is stored in the ROM because the content needs to remain and stay there when there is no power.
Describe the purpose of RAM in a computer system
A computer system needs to store programs and data when it is running. The speed of the computer system will be limited by the speed of this storage RAM is used because it offers a good compromise between cost and speed. It also fetches instructions and transmits them to the cache memory thus to the CPU so it works in the fetch and execute cycle.
Explain how the amount of RAM in a personal computer affects the performance of the computer
The more RAM there is, the more programs can be running simultaneously.
OR: As operating systems systems on desktop computers get more and more complex, they need to use larger and larger amounts of storage to run their programs. Adding more RAM means that the data doesn't need to be swapped as often so the system will run faster.
Explain the need for virtual memory
If RAM is not large enough to store all of the data and instructions that it is required to store, virtual memory may be used. This is when the hard disk is used as an extension of the RAM and temporary gives memory addresses as if it were RAM. This technique can be done by modern operating systems.
Describe cache memory
Cache memory is a high-speed store of frequently used programs by the processor of the CPU. It stories copies of data or instructions from the RAM. It has the fastest access speed for memory and will usually be small. It is expensive.
Describe flash memory
Flash memory uses electronic chips as storage. It is non-volatile and is a portable, solid-state memory technology. Examples of flash memory are USB drives which are frequently used to transfer data between computer systems and memory cards. Memory cards can also be used by computer systems but they are more commonly used to provide storage in devices such as digital cameras and to expand the storage capacity of tablet computers. Flash memory can be erased and re-programmed. Mini SD cards also use flash memory often found in mobile phones.
Discuss how changes in memory technologies are leading to innovative computer designs
Many modern computers use flash memory for the ROM which allows the contents to be updated using 'flashing'. Moreover, memory technology is getting faster, cheaper and smaller. Therefore, we get faster, cheaper and smaller devices such as tablet PCs, smart phones and larger USB pen drives.
Understand the need for input and output devices
Computers only work with digital information. Any input that a computer receives must be digitised as computers can only understand two states: on or off thus 0 and 1. The digital signals only have two states 0 and 1 like binary and the computer can only understand instructions in binary. Often, data has to be converted back to an analogue format when it's output. Output devices are needed to produce a form/display that is understandable to the user whereas input devices are used to enter data onto the computer which it can understand (binary).
Describe suitable input devices for a wide range of computer controlled situations
MAINSTREAM
MOUSE: Use to move a cursor and select icons on a GUI.
Advantages: Excellent option for users on desktop computers and appropriate users in seated position.
Disadvantage: need a flat clean surface.
KEYBOARD: Use to enter text and numbers into a computer system.
Advantage is that it is a reliable form of data entry so an A will only mean an A
Disadvantage is it is slow to enter text/numbers. The user is very prone to errors and is not good for users with poor dexterity (poor finger control).
SPECIALIST
TOUCH SCREEN: users can drag, select, expand items without an additional device. It is very intuitive and no additional devices are required. A disadvantage is that is does not work if fingers are went or if the user is wearing gloves.
SENSORS: Used to capture the movement of the user. An advantage is that the user can control a computer system without contact with a device. Disadvantage is that the gestures can be misinterpreted by the system and they often require light.
OMR (Optical Mark Recognition) Scanners are devices which recognises marks on a document which correspond to data. They are often used in surveys/multiple choice questions.
Barcode Scanner: Scans the widths of the lines and spaces. These widths represent a unique code. When the code is captured by the scanner, the code is looked up in a database and the item information is displayed.
RFID (Radio Frequency Identification) - Tags are placed on items and the tags themselves stores data/unique code like a bar code. Unlike a bar code, these tags don't need to be in line of sight of the scanner. The scanner sends a signal to the tag and receives a response which is the code.
Describe suitable output devices for a wide range of computer controlled situations
Monitor: Displays information via pixels on a screen. Pixels continue to present us with languages that we can recognise and gain information from. Used in a wide range of areas like home and office. It usually accompanies with a desktop computer.
Projector: presents an image on a screen/wall/object which we recognise and can gain information from. It is used in cinemas, schools, video conferencing etc.
Printer.
SPECIALIST/INDUSTRY OUTPUT DEVICES
Actuators: these are output devices which produce movement/motion. For example they are used to control the flaps on the wing of the plane to drop if the autopilot senses an increase or decrease in altitude.
Plotter: It is a specialist output device which prints huge images onto massive sheets of paper. They are used to create technical drawings or blueprints.
Discuss input and output devices for users with specific needs
INPUT DEVICES
Such-puff-switch: Paralysed users can use their mouth to control a switch. Programs can interpret these inputs to carry out a number of tasks.
Eye-Tracker: Cameras locate the eye and the direction that the person is looking. The cursor will follow the eye movement. Staring at an icon will select it.
Foot Mouse: Users with limited arm movement can use their feet to control and select icons.
Braille keyboard: Users with poor sight can use two types of keyboards: normal keyboard with braille to guide them to the correct letter or a keyboard which the user can select the position of the dots to create each braille letter.
OUTPUT DEVICES
Braille printer: These work by punching holes or raising them using software, to form the Braille that someone who is visually impaired can feel and interpret as information thus understand.
Voice Synthesis: These output devices which is a speaker and screen combined allow users who cannot naturally communicate to pick letters and words from a screen. The synthesiser will then synthesise human speech to speak the letters/words aloud.
Screen Magnification: Screen magnification software will adapt the screen so that partially sighted people can more easily read the information on the screen.
Screen Reader: Like the screen magnification software, this adapts the output device (screen) to present the text in a 'spoken' form.
Explain the need for secondary storage
Secondary storage is needed because it is non-volatile so it won't lose its content when the computer is turned off. Therefore, the secondary storage devices can save all the data in its original form. This is needed for two main reasons: The computer's working memory is finite and limited in size so it cannot always hold the data we need.
Also, remember that secondary storage refers to storage devices and media that are not constantly accessible by the computer system like CDS, portable flash frives, external had drives etc.
Describe common storage technologies such as optical, magnetic and solid state
OPTICAL storage media, including CDs, DVDs and Blu-Ray disks are written to and read from using lasers. Optical disks spin to allow the laser to read the data from the correct location. The surface of the disk will have billions of locations in which holes can be physically burned by a laser or not burned which can represent either 0 or 1 thus binary instructions.
MAGNETIC storage devices: the disk will spin at a high speed under the read/write heads which is symbolic of the north and south poles thus 0 or 1 states of binary instructions.
SOLID STATES: have no moving parts and all storage technologies including solid states are non-volatile. Solid state uses electronic circuits. These devices are both sturdier and quieter than magnetic or optical devices.
Select suitable storage devices and storage media for a given application and justify their choice using characteristics such as capacity, speed, portability, durability and reliability.
SOLID STATE like usb pen drives:
Capacity - typically range from 1GB to 64GB, but higher capacities are always being developed.
Speed - could be around 5 million bits per second,
Portability- very small and light so it is designed to be moved between computers.
Durability - very durable and strong.
Solid state devices are useful for people who do not always work at the same computer but always need access to their work.
OPTICAL DISKS
Capacity - CDs: 700MB DVDS: 4.7 GB and Blu-Ray disks - 25GB
Speed - highly variable although Blue-Ray drives are much quicker than DVDs or CDs
Portability - small and light but not as easy to carry as a USB flash drive.
It is also compatible with several devices.
Durability - quite sturdy although if the surface is scratched the data can be irretrievable.
MAGNETIC like an internal hard disk drive
It is cheap
Capacity is very large, like terabytes.
Speed - data transfer from an internal drive is usually far quicker than any external device.
Portability - it is difficult and time-consuming to move an internal drive from one machine to another
Durability - very well protected inside the computer and protected by a metal case when removed.
Explain the need for the following functions of an operating system:
User interface: communication between computers and the user. An interface makes computers user-friendly.
Memory management: one of the main functions of the operating system - managing multiple applications using the space in main memory so all programs can be executed efficiently.
Peripheral management: one of the main functions of the operating system: managing the input and output of the CPU.
Multi-tasking: one of the main functions of the operating system: managing how several programs which are all running at the same time, share the processor.
Security: one of the main functions of the operating system - protecting the computer system from various hazards such as unauthorized users, viruses, hackers and accidental damage.
Describe the purpose and use of common utility programs for computer security
Anti virus: capability to guard against malicious software and it is a utility software which prevents harmful programs being installed and important files from being changed. If a virus does enter the network or computer, the anti virus software detects it and removes it. A virus is a program that is installed on a computer without your knowledge or permission and with the purpose of doing harm. It includes instructions to replicate automatically on a computer and between computers.
firewall: to protect against both software and remote hackers.
Password facilities: different users have their own usernames and passwords and only be allowed access to things they need to access.
Spyware protection stops unauthorized users from accessing the user's actions on their computer system and watching what they do without the user's permission (so they can not access the user's history for instance).
Disk organisation
An operating system is responsible for making sure files are stored in a hierarchical structure.
Operating systems also provide the user with means by which to locate files. If files are stored in a hierarchical structure, they are quicker to be searched through and can be found easier if the user is looking through each sub directory manually.
The top level of the hierarchy is called the root directory, beneath which are sub directories
Moreover, defragmentation. It is a utility program that optimises the use of the hard disk space by grouping together the separate parts of each file in one location on the disk as well as grouping together the space so newly saved files do not have to be fragmented (split up). It also quickens the time it takes to access files.
File transfer: the operating system is also responsible for moving files, both physically and physically on the disk and conceptually within the direct structure. An operating system will also be capable of moving a file from one device such as an internal hard drive to another such as a USB flash drive.
Disk formatting: formatting a disk means permanently deletes everything from it and making it ready to have new files saved to it. This process is managed by the operating system although the operating system itself is on the disk being formatted. It guarantees that viruses and other malware are removed. If a disk is going to be disposed of, it ensures all personal data is deleted. Sometimes, a disk is formatted as part of the process of installing a new operating system.
System maintenance
System information and diagnosis utilities prove information to the user and any other software about the computer, such as the hard disk capacity, processor speed and the name of the operating system.
System cleanup tools are essential along with regular fragmentation to keep a computer operating efficiently. Files that are no longer needed can be deleted.
Automatic updating ensures that a computer always has the most up-to-date version of a program available. Newer versions of programs might run quicker have more features and have better security or bugs removed. This utility is found more and more often in mobile phones as well as computers.
Discuss the relative merits of custom written, off the shelf, open source and proprietary software
Custom written software is produced specifically for you. It is expensive and takes a great deal of time to use the software. Moreover, the software is designed by the developer specifically for the purpose of the user's request.
Off-the-shelf software which is also proprietary software is the kind that you buy from a shop or pay to download it. It is quick to access and the errors are easy to fix through online forums and user manuals, unlike custom written software. It is cheaper although there is a possibility that it may not do everything you want it to do.
Open source software gives you access to the source code and allows you to make changes to customize to meet your exact needs. It is free although you would need a high level programming skill to be able to customize it.
Moreover, proprietary software is software that legally remains the property of the organisation, group or individual who created it, They do not release the code but insist only those who have bought the special license can access the program. The source code is not often sold but remains with the administrators of the computer.
The advantages are that it gives software developers an incentive to produce quality software because the developer is looking for profit. However it costs and the license does not allow the user to modify the software or to figure out how the software was made,
Define the terms bit, nibble, byte, kilobyte, megabyte, gigabyte and terabyte
Bit - 0 or 1 binary digit.
Byte - 8 bits or two nibbles
Kilobyte - 1024 bytes
Megabyte - 1024 kilobytes
Gigabyte - 1024 - megabytes
Terabyte - 1024 gigabytes
Understand that data needs to be converted into a binary format to be processed by a computer
Computers work by processing electrical signals
Electrical signals can be either on or off
Text, images, sound and instructions all need to be converted into binary so that computers can understand the information. Rows of binary are symbolic of instructions.
Explain overflow
When the result of a numeric calculation s too large to be stored in the space reserved for that type of data. What happens when overflow occurs? The user will see an error message saying 'overflow' has occurred and the computer may ignore the ninth bit,
Explain the use of binary codes to represent characters
A database will store the binary instructions for each letter. Computers can only understand binary so each binary instructions of O and 1 can equivocate to letters so the computer can understand the user's entry. A standard set of numbers used to represent each letter would mean that is is compatible between different devices
Explain the term character set
Character set is the group of symbols, letters, commands on a computer which is represented by a computer. Each character is assigned to a binary instruction. So, it is an agreed standard for how and which numbers represent each character.
Describe with examples (for ASCII and Unicode) the relationship between the number of bits per character in a character set and the number of characters which can be represented
ASCII
American Standard Code of Information Interchange
7/8 bits
256 possible values - extended ACII
normally 128 possible values.
However, originally it was worth 7 bytes and had 128 values,
It is enough to represent the whole of the English language but was not representative of other languages and accents for instance.
Unicode
It can store many more characters
16 bytes
Can cover several languages
Do two to the power of 16 to get the possible values.
Explain the representation of an image as a series of pixels represented in binary
An image is divided into pixels, each of which is a tony dot on the screen. A pixel is short for picture element. It is the smallest component of a bit-map image. A pixel can only be one color at a time, and when the picture is saved, the colour of each pixel must be stored in binary, When there more bits that are used to store each pixel, the more colours are potentially available.
Explain the need for metadata to be included in the file such as height, width and color depth
The metadata is needed in order to load the image, while date and time are helpful in making image files on a disk more searchable
Discuss the effect of color depth and resolution on the size of sound file and quality of its playback
Color depth - the number of bits used to represent the colour of a single pixel in a bit-mapped image. Higher colour depth gives a broader range of distinct colour. When more colours are needed, more bits are needed. Many images store 24 bits therefore three bytes for each colour. The more variety in the pixel, the greater the colour depth - like a certain shade of blue will use more pixels than the normal colour blue, assumed by the computer.
If we double the resolution of an image, we quadruple the amount of data that is needed to store the image because: 16 pixels wide
16 pixels high
2colours
16x16x1 bit = bits 256 (32 bytes). The resolution of an image means the number of pixels in an image expressed as the number of pixels across x the number of pixels down.
Explain how sound can be sampled and stored in digital form
Sound is a pressure wave in the air. It is continually changing which we call an analogue signal. To record the sound on a computer, we need to convert the analogue sound into numbers (digital). You may use an analogue to digital converter which can be found using the input device: microphone.
Explain how sampling intervals and other considerations affect the size of a sound file and quality of its playback
The term sample rate or sample interval are the same. They both are the time gab between measurements of the sound wave being taken. Within the sample interval, the computer includes the volume and frequency of the sound and records the sound wave multiple times per second.
A higher sampling rate results in better sound quality but requires more storage space.
Bit rate
It is how many bits are used for each sample (measured in bits per second) and this can vary widely. Again, higher bit rates result in higher quality of sound but also higher storage requirements.
So, overall. To improve the quality of the recorded sound, we can sample the sound more frequently. If you double the recording interval, the double amount of data is stored or the audio file. Additionally, we use a greater number of bits to record the sound more accurately which results in a higher resolutions.
Explain how instructions are coded as patterns
The computer can only understand binary which are single digits of 0s and 1s. Therefore, patterns of 0s and 1s are used to create instructions with the computer can understand and process. The OS will have a table of instructions which may be entered as words but the string of words may be assigned to a binary value.
Explain how the computer distinguishes between instructions and data
Every computer program is made up of instructions and data. The instructions tell the computer what to do and the data might be text, number, image or sound that the instructions are applied to. Both instructions and data will consist of a sequence of 0s and 1s. The computer needs a way to distinguish between them so each instruction and each piece of data will be stored in a specific location on the disk with a specific memory address. The OS keeps track of which memory addresses contain instructions and which contain data.
Describe a database as a persistent organised store of data
A database is a persistent, organised collection of related data.
Persistent ----> Non-volatile, stored on secondary storage such as a hard drive, more than one person can access the database at once.
Organised-----> Has "records". Can be searched, modified and deleted.
Store of Data------> Its stored and data can be anything pictures, text and music.
Explain the use of data handling software to create, maintain and interrogate a database
The use of handling data software such as a DBMS creates, maintains and interrogates a database. For instance, create means to set up the structure of the database such as tables and forms. Maintain means to update the database, edit records, add records and delete records. Interrogate means to search for data that matches certain criteria. These qualities of a data handling software are useful because they ensure data integrity, efficiency and persistence.
Moreover, storing data in a database is advantageous because data can be accessed speedily and manipulated to form new data. A single database can be shared. Moreover, data validation can take place which ensures the data is integral.
Describe how a DBMS allows the separation of data from applications and why this is desirable
DBMS stands for database management system.
This means that actual data is stored separately using the tools to view, edit and upgrade the data. Keeping the data and the program separate is a good thing because the program could be updated or even replaced with a new program and the data would not need to change. Similarly, if the data needs to change at any time, the program does not need to be altered in anyway.
Furthermore, a DBMS is a piece of software that sits between an application (the program the user works with) and this file system (the data itself).
APPLICATION
^^^^^^^
DBMS
vvvvvv
FILE SYSTEM
Describe the principal features of a DBMS and how they can be used to create customised data handling applications
Features of a DBMS includes:
- Separating applications and data. This means that applications simply call on the resources from the database so both can be updated without affecting each other. When I say both, I mean the data on the database and the application per se.
- Allowing more than one person to use the database at once.
- Setting up access rights so some users will be able to delete and change records, others can only view it or even be forbidden from viewing it. The DBMS ensures security and therefore protects the data.
- Allows the data to be queried through SQL
- Allows reports to be generated which presents particular fields to the user - outputs.
Understand the relationship between entities and tables
An entity is a real world object that can be separated into other parts of data. An entity is represented in a database by a table.
Understand the components of a relational database, such as tables, forms, queries, reports and modules
In relational databases, they can have more than one tables.
Reports are used to output data items from the database. This might be on the screen or some fields may be printed out on a neatly formatted document. The report can show information from tables or queries. It allows chosen data items to be displayed and edited or specified fields laid out in a specified format.
Moreover, a form is an input screen, allowing chosen data items to be displayed and edited. It uses text boxes and drop down lists. When edited, the changes are updated on the database.
You may give examples in the exam.
A table is a collection of data organised into records and fields within a relational database. A table represents a real-world entity.
Queries are a form of selecting certain pieces of data within the database by using particular commands. It allows the database to be interrogated. It selects records from the database based on a specified criteria.
Moreover, modules are a pre-written set of code which manipulates data in a specific way that is not directly catered for by the database software. They are quicker to enter data onto a database.
Understand the use of logical operators in framing database queries
= means they are the same
> greater than
< less than
<> not equal to
<= less than or equal to
>= greater than or equal to
Explain the use of key fields to connect tables and avoid data redundancy
A table has a primary key which is a field that uniquely identifies a record.
A foreign key is a field in one table that is a primary key in anothe table. It is used to create a relationship between the two tables therefore connecting the tables together.
This, therefore avoids data redundancy as all the data from one table is not copied into the other. So if one table is updated, all the data in other tables containing data from that updated table, will also have the data updated. No data will be left behind and become redundant.
Describe methods of validating data as it is input
When data is entered in to a database, validation checks can be conducted on that data to check that it is reasonable and sensible (a validation check does not necessarily make sure that data being entered is correct). Validation checks ensure that the data is 'valid'. See it? :P
So, the validation checks to know can go under the acronym FLIRT PS
Format Check - some pieces of data are formed of characters in a specific order like for telephone numbers
Length Check - whatever is entered into a field has to be a certain number of characters long.
I
Range Check
Type Check - will make sure that a field has been completed with the right kind of data (a number, or text).
Presence Check can be used to make sure that something is actually filled in when a new record is entered. This is often used for long text fields.
Select from a list check or lookup which proves the user with a drown-down list from which to select the desired option.
Imagine the only vowel which is I.
Explain the advantages of networking stand-alone computers into a local area network
- You can share peripherals like printers which reduces costs because all the computers are connected.
- You can share an internet connection
- You can share files and folders securely so you can access your own documents and shared documents from any computer on the network
- Communication: instant messaging so you can use messaging systems to chat while you are working on each others things
- Using e-mail to communicate with colleagues
- Users can use any PC on the network and still see their own files
- User profiles and security can be managed centrally.
- Centralised backup of all files which prevents downtime if the computers were to fail, the data could be recovered.
- Software care be distributed across the network rather than having to install it on each computer.
Describe hardware needed to connect stand-alone computers into a local area network including hub/switches, wireless access points
Hub - is a rather unsophisticated device which enables packets of data to be sent to different computers.
Switches - Are more sophisticated than hubs as they control which data packets are being sent to each node and allow packet switching so packets of data being transmitted to other nodes on the network.
Wireless Access Point - the device to which a computer connects wirelessly. Can be a wireless hub or switch. It uses signals in the form of radiation and these signals can be intercepted. Using a hub is a way quicker form of gaining internet access.
Cables - UTP (Unshielded twisted pair). A wire which transmits electrical signals. A UTP is fairly easy to install and upgrade, whilst being cheap.
Router - hardware device which provides connectivity from a LAN to the internet. Use internet protocol (IP) to communicate with each other.
Modem - the hardware device used to convert the digital transmission of a computer into an analogue signal that can be carried over the analogue telephone network. A method of accessing the internet.
NIC - Network interface card which has a ROM chip within it. It has a permanent 48 bit address - numerical code called a MAC address which identifies nodes and peripherals like printers on the network.
Explain the different roles of computers in a client-server and a peer-to-peer network
In peer-to-peer, all computers have equal status. All of them can store files, and any peer can transmit a file to another node on the network. This model is generally less secure than a client-server model, where security can be concentrated on the machine that holds all the files. There is also an issue of duplication, as you can see, but this can be a good thing. If one peer were to go offline, the other nodes can access the files.
In client-server, there is a specialised, high specification computer which handles the central storage and processing of shared files and services such as printing. It saves a great deal of energy as virtual servers can be used which partitions the functions of several servers, into one.
Describe, using diagrams or otherwise, the ring, bus and star typologies
Don't forget the most common cable used in a bus is a UTB (Unshielded twisted pair). It is easy to add or remove computers. A bus topology uses a central data bus cable to connect the computers. It is cheap as it requires minimal amount of cabling. Each computer, server printer etc is connected to the bus. Bus networks are slow because only one computer can use the bus at once. If the bus fails, then the network will also stop working.
Don't forget the most common cable used in a bus is a UTB (Unshielded twisted pair). It is easy to add or remove computers. A bus topology uses a central data bus cable to connect the computers. It is cheap as it requires minimal amount of cabling. Each computer, server printer etc is connected to the bus. Bus networks are slow because only one computer can use the bus at once. If the bus fails, then the network will also stop working. 
Each computer is linked to each other in the form of a ring. There are no data collisions, as there is typically only one batch of data allowed on the network at any one time. Very high rates of transmission are possible. One disadvantage is that only one computer can use the network at once which makes it very slow. If one computer fails, the whole networks stops working. In addition, security is not ensured as data passes through other devices en route to its final destination.
A star network has a central hub or switch that all the computers are connected to. The switch looks at the data that is being transmitted and only sends it to the computer who it is intended for.
An advantage is that faults are easy to find whilst it is easy to add extra devices. Moreover, the system is secure as data is only sent to devices that need data. This mean that the network runs a lot more faster and that the network will not be disabled by one faulty computer. Requires more cable length than a linear topology which can be more expensive. If the hub or switch fails, nodes attached fail. More expensive than linear bus topologies because of the cost of the hubs, etc.
Describe the differences between a local area network and a wide area network such as the internet
A local area network is a small group of computers which are connected together over a single site. The infrastructure is often owned by the network creator whereas with WANs, the infrastructure is often leased. Moreover, with WANs, they are often LANs connected to each other to form a WAN. WANs also cover geographic areas as opposed to a single site. In addition, for WANs, extra technology such as satellites, microwaves and telephone cables are used to link them together.
Explain the terms IP addressing, MAC addressing, packet and protocols
IP addressing - a method of labelling any device connected to the network with a unique numerical value.
Uses four bytes
MAC Address: A unique hardware number allocated to every NIC. It is a 48 bit address usually written in hex.
Packet: a fixed size chunk of a message created to send over a network. It has its own header containing data such as the destination address and packet number so the message can be put together in the right order. There are several advantages for having packets:
The header includes the source address and destination address of the packet, as well as an identification number, needed to re-assemble data that has been split once transmission is complete. Transmitting data has a number of advantages:
- The packets do not need to take the same route around the network as each other
- The packets do not need to arrive in the same order that they left, as they are reassembled by the recipient computer.
- If one packet is not delivered correctly, only the packet needs to be re-sent, not the entire piece of data.
Protocol - a set of rules that defines how each device communicates.
Some protocols to remember:
HTTP - Hypertext Transfer Protocol. This is the set of rules governing how hypertext (the language of the worldwide web) is moved around the internet from device to device.
POP 3 - Post Office Protocol Version 3. This is a protocol for accessing emails and is commonly used in Microsoft Outlook to take the emails from an online location and open them in an Outlook environment.
FTP - File Transfer Protocol. This is how files are moved from one computer to another across the Internet. This protocol is heavily relied upon in building websites, moving files from one developer's computer to a server where they can be accessed publicly.
SMTP - Simple Mail Transfer Protocol. While POP3 might be used to retrieve emails, SMTP is used to send them from one server to another.
Explain the need for security measures in networks such as user access levels, suitable passwords and encryption techniques
Username and passwords should be changed regularly and be very strong. The passwords should include a range of characters like numbers and capital letters. It only allows you to use the system if you are authorised. The network administrator will decide on the passwords.
Moreover, encryption prevents hackers from understanding any data if accessed (e.g passwords). When data is sent on a network, it can be intercepted. It would be quite easy to read the data and gain unauthorised access. Networks can encrypt the data in a way that makes it impossible to read the data without the necessary key.
Access rights prevent files from being modified/deleted and even viewed by some users.
User access control prevents users from making changes to the system.
The network administrator may create a set of policies that all users are supposed to adhere to.
Describe ad justify network policies such as acceptable use, disaster recovery, fail over, back up and archiving.
In terms of acceptable use: the network administrator may create a set of policies that all users are supposed to adhere to. This policy sets down what users are permitted to do and not permitted to do within a network. The policy document may include the following:
- whether or not users are allowed to play games, use instant messaging services or access certain websites
- What personal information should be entered or not be entered onto the network.
- What sanctions (punishments) might be applied to users who violate the acceptable use policy.
Backup - a backup policy states what data will be backed up from the network, how often it will be backed up and where it will be physically stored (ideally in a fireproof, cold and locked up room) and how it will be used to restore any lost data. Without a backup policy, data is more likely to be permanently lost.
Failover - sometimes, a computer, other device or communication media such as an Ethernet cable will stop working correctly, and a fail over policy contains information on how to keep the network functioning if this happens. Files need to still be available and devices still need to communicate with one another, even in the event of such network failures. A critical component can be backed up with a spare, so that in the event of a failure, the system can switch ovr from the on working to the working component which is fail over.
Disaster Recovery - the policy describes how an organisation's IT infrastructure will keep an organisation running in the event of a disaster along the lines of fire, flood or earthquake. Such a policy may contain parts of the backup and failover policies, and is important because an organisation without IT capability is likely to lose income as well as people's trust in their ability to operate.
Archive - an archive is a long-term storage of data that is not needed on a day-to-day basis any more. An archive policy will stipulate what data is to be archived, where it will be stored and how old data needs to be before it is archived, Sometimes, for legal reasons, organisations need to keep data for longer than it is useful to them.
Describe the nature of the internet as a worldwide collection of computer networks
The internet is simply a worldwide network, containing many millions of computers ad related hardware such as routers, switches and mobile devices. The internet is a huge collection of computer networks and arguably, LANs.
Describe the hardware needed to connect the internet including modems and routers
When you go to a webpage, your computer becomes a part of the internet. In order to connect to the internet, you need a router which forms a connection between either a LAN or a stand-alone computer and the rest of the internet. If you are connecting to a communication line that does not work with digital signals (binary), such as a standard telephone line, you would need a modem (modulator demodulator). This device converts signals from digital to analogue which the telephone line uses. The telephone line carries the signals.
A modem was slow and unreliable as you could not use the phone and internet at the same time. It was pretty expensive because you had to pay for the phone call. When the broadband became available, the modem was replaced with a router. The router allows you to keep using the phone while you connect to the internet. It also transmits the signals in a digital form so it is much faster.
Explain the need for IP addressing of resources on the internet and how this can be facilitated by the role of DNS services
DNS servers have a database of IP addresses which are constantly updated by other DNS servers. When you request an address (URL), the DNS server looks up the URL and returns the IP address, or searches for the address from other DNS servers.
People, therefore, do not need to remember IP addresses.
It is easily upgradable from IPv4 to IPv6 without all web addresses needing to be the same.
As long as you are connected to a DNS server, you can have access to all addresses.
Explain the importance of HTML and its derivatives as a standard for the creation of web pages.
HyperText Mark-up Language
Text file containing the text to be displayed
uses tags which indicate how to display it
location of pictures or other elements too.
Using HTML, you can also establish hyperlinks to other locations/URLS.
Moreover, the web browser used to interpret the file and display the data correctly because it is an open standard and the data will display correctly on all browsers which conform to the standard hence why HTML is important in webpages.
Describe common file standards associated with the internet such as JPG, GIF, PDF, MP3, MPEG
JPG - Joint Photographic Experts Group - Is a file format for images that allows photographs to be stored using less space than with other file formats - it undergoes lossy compression.
GIF - Graphic Interchange Format - This is another image file format that is better suited to graphics rather than photographs. animated, moving pictures can also be stored as GIF. GIF works best for images with large blocks of the same colour which tend to be images that are hand drawn,
PDF - Portable Document Format - This format is well suited to documents to be read. It is very popular online as the software to access PDFs are usually free. Additionally, PDF are platform independent, this means that any computer, running any browser or PDF reader, will display the document in the same way even when printed. PDF files are compressed.
MP3 - Music player layer III - This is the most popular file format for storing music online. The quality is not as good as the WAV format but the file sizes of the MP3s are small, thus quicker to download. Heavily compressed using a lossy method.
MPEG - The Moving Picture Expert Group - Video that is compressed using the lossy method.
Explain the importance of compressing files that are transmitted via the internet
Compressing a file over the internet is important because:
It reduces the size of the file which needs to be transmitted Shortens download time Reduces Internet traffic (and hence probability of lost packets) Allows multimedia files to be streamed.
Directly from mark scheme^
Describe the difference between lossy and lossless compression
In lossy compression, when the data is uncompressed it is not exactly the same as the original but the difference is so small that is cannot be normally noticed. Music files such as MP3 or large resolution images for displaying on small screens used lossy compression - this will reduce file size.
In lossless compression, when the data is uncompressed it is restored completely to the original file.
An example of lossless compression is compressed text files.
Understand algorithms (written in pseudocode or flow diagram), explain what they do, and correct or complete them
Algorithms are a series of steps to solve a problem. Can be expressed in structured English, pseudocode or as a system flowchart.
Algorithms solve problems on a computer.
Explain the difference between high level code and machine code
High level code is written in a which which humans can understand. Programming languages are high level code. A CPU can not use a high level language so it needs to be translated into machine code which is the only language the computer can understand. High level uses words. The code is designed to be read by human programmers. High level code is also portable and can be translated for different machine.
They resemble natural language.
Examples: Java, Visual Basic, Python, C#
Either an interpreter or compiler is needed to translate the code into machine code so that the computer can run it.
----------
LOW LEVEL :
Machine code is the binary that the CPU decode and executes when it runs the programs. Machine code is specific to a particular machine.
It is more difficult to understand but can often be executed by computers very quickly.
Examples: Machine code and assembly language
Machine code does not need to be translated as it is machine ready.
Assembly language requires an assembler.
Explain the need for translators to convert high level code to machine code
Low level - Machine Code
Mid Level - Assembler
High Level Lang - Python, JavaScript etc
Computers run using instructions written and stored in machine code.
Humans can create programs using an assembler and even machine code although it is difficult and takes a great deal of time.
Low level - Machine Code
Mid Level - Assembler
High Level Lang - Python, JavaScript etc
Computers run using instructions written and stored in machine code.
Humans can create programs using an assembler and even machine code although it is difficult and takes a great deal of time.
- A compiler converts a whole program from source code (the code that the programmer types) into machine code. If there are any errors int he code, the program will not compile, and the programmer will have to remove these errors before trying again.Translates the whole program to produce to produce the executable object code which is the version that the computer runs. Faster run time because the program is translated once, the object code is run after that. Customers cannot see the actual code that you wrote when distributing the program. It is used for distributed software.
- An assembler is used to convert assembly language to machine code. Assembly language is in the form of mnemonics.
Describe common tools and facilities available in an integrated development environment (IDE): editors, error diagnostics, run-time environment and auto-documentation
IDE is the program that brings together a broad range of software development tools to allow the programmer to write programs without having to rely on lots of separate utilities.
Editor : In this particular environment, this can switch between text editor, where the code is entered and GUI, where you can drag and drop controls such as text boxes and buttons.
Error Diagnostics:If any errors within the code are detected, they are brought to the attention of the user. Some IDEs even offer the user possible solutions to an error.IDE is the program that brings together a broad range of software development tools to allow the programmer to write programs without having to rely on lots of separate utilities.
Editor : In this particular environment, this can switch between text editor, where the code is entered and GUI, where you can drag and drop controls such as text boxes and buttons.
Run-time environment: Allows you to run your program as you are creating it, by pressing 'play' button or equivalent.
Translators: form part of the IDE.
Auto-documentation features include automatically creating parts of the maintenance documentation for your program as you type code.
Understand and use sequence in an algorithm
When instructions are executed one after another in series without conditions.
Understand and use selection in an algorithm (IF and CASE) statements)
When the program will execute certain instructions based on conditions. Selection statements include IF.. THEN.. ELSE and CASE... OF to select which commands to execute.
CASE MenuChoice OF - This will compare a value
1: OUTPUT "Menu Choice 1"-if it's "1", this will happen...
2: OUTPUT Menu Choice 2"
3:OUTPUT Menu Choice 3"
END CASE
In terms of normal if statements, you can do the normal, IF THEN ELSE ENDIF..
Understand and use iteration in an algorithm (FOR, WHILE and REPEAT loops)
Where a program will execute a group of instructions zero or more times based on a condition. FOR loops will execute instructions a specific number of times, REPEAT... UNTIL loops for one or more times and WHILE... DO loops for zero or more time.
REPEAT
name = ..
passwords = userinput
UNTIL password=correct
The test is done at the end.
WHILE COUNT... DO ###count is a number
OUTPUT..
COUNT...It is important that whatever you are testing will be changed in this block, otherwise your loop will iterate forever.
END WHILE
FOR Count = 1 to 10 DO
OUTPUT
OUTPUT COUNT
Define the terms variable and constant as used in an imperative language
The value of a constant is set when the constant is declared
The value of a variable is set while the program is running
The value of a constant cannot be changed once the program is running/can only be set at design time A variable has no value at design time.
A value that does not change (while the program is running)
A location in memory to store / a value that may change (as the program is running)
Those answers were from the mark schemes.
A constant also refers to data that is stored in the computers memory..
Describe the data types integer, real, Boolean, character and string
Integer is a data type for whole numbers. It is often stored in memory by splitting up the binary number into 8 bits.
Real number is a data type for fractional numbers, typically 4 bytes.
Boolean is a true or false value, typically 1 bit.
A character is a single letter, number or punctuation mark, space etc. It requires one byte. Examples of character data might include 'M' or 'F' to represent gender.
String is the data type for text, more than one character. It takes up 1 byte of character.
Perform common operations on numeric and Boolean data
There are two other common operations that we can perform on numeric data:
DIV - integer division - same as a normal divide but forget part of the answer after the decimal.
MOD - Modulo calculates the remainder, as a whole number.
These two operations can be performed on real and integer numbers but both given integer answers.
Use one-dimensional arrays
An array is a group of data items of the same data type that uses a single identifier. Individual data items are accessed using a subscript.
The index values for arrays start at zero.
Arrays can be one-dimensional, in which case each element is accessed by a single number.
Describe syntax errors and logic errors which may occur while developing a program
Syntax error: an error in the format of the program statements such as missing semicolons or keywords spelt incorrectly. You can also say a syntax error are when the rules of the language have not been followed. If the code is erroneous, it will either not compile, or it wish crash when the line of error is reached.
Logic error: an error in the algorithm that means the outcome is not as expected, even though the program will run.
Select and justify test data for a program, stating the expected outcome of each test
Type of test datas: typical, extreme and invalid entries. Before a program is tested, a testing table is usually drawn up which contains the following headings:
test descriptions, test data, expected outcome, actual outcome.
Sources are from ZigZag education, OCR and Riddlesdown.org :)
No comments:
Post a Comment