Computing Key Terms and Definitions

Computing Key Terms and Definitions

1. Basic Model

   • Computer System
     • A combination of hardware and software components that allow input, processing and output of data.
   • Hardware
     • The physical components that make up a computer system.
   • Software
     • The programs that run on a computer system.
   • Input Devices
     • Hardware devices that take real-world analogue data and convert it into a digital from that can be stored on a computer e.g. keyboard, mouse, microphone, webcam, scanner etc.
   • Output Devices
     • Hardware devices that use digital data from a computer to produce a form that is understandable to a person e.g. monitors, printers, speakers, projectors etc.

2. Importance of Computers

   • Reliability
     • How much you can depend on the computer system being available when you need it. Usually measured in terms of availability.
   • Availability
     • The proportion of time that a system is operational, usually expressed as a percentage over a certain period of time e.g. 95% over 1 year.
   • MTBF
     • Mean Time Before Failure: a measure of availability often quoted by hardware manufacturers. For example, 2.56 years between failures means that on average, the hardware can be expected to last 2.56 years before it goes wrong.
   • Redundancy
     • Spare hardware components that are built into a system so, in the event of a component failing, the system can swap over to the spare one.
   • Disaster Recovery
     • Where a company has plans to replace a system quickly if there is a catastrophe (fire, flood, bomb etc). designed to minimise the time the system is down.

3. Units

   • Bit
     • A single binary digit (0 or 1)
   • Nibble
     • 4 bits (half a byte)
   • Byte
     • 8 bits
   • Kilobyte
     • 1024 bytes
   • Megabyte
     • 1024 kilobytes
   • Gigabyte
     • 1024 megabytes
   • Terabyte
     • 1024 gigabytes

4. Numbers

   • Binary
     • Base 2 number system. Used by computers and uses the digits 1 and 0.
   • Denary
     • Base 10 number system. How human normally count and uses the digits 0 to 9.
   • Hexadecimal
     • Base 16 number system. Used by humans to represent groups of four bits at a time and uses digits 0 to F.
   • Overflow
     • When the result of a numeric calculation is too large to be stored in the space reserved for that type of data.

5. Characters

   • Character Set
     • The set symbols that can be represented by a computer. The symbols are called characters and can be letters, digits, space, punctuation marks and some control character such as ‘escape’. Each character is represented by a numerical code that is stored as a binary integer.
   • ASCII
     • American Standard Code for Information Interchange: a 7-bit character set used by PCs. (There is also an extended ASCII character set that uses 8 bits).
   • EBCDIC
     • Extended Binary Coded Decimal Interchange Code: an 8-bit character set used by older mainframes.
   • Unicode
     • A 16-bit character set that allows many more characters to be coded.

6. Images

   • Bitmap
     • An image that has been stored as a series of values per pixel. The colour of each individual pixel is stored in a file.
   • Vector
     • An image file that is made up of lines and shapes that have certain properties, for example, a line may have the following gproperties: start-point, end-point, line colour, line thickness, line style. The properties of each shape are stored in a file to make up the image.
   • Pixel
     • Short for picture element. It is the smallest component of a bitmap
   • Colour Depth
     • The number of bits used to represent the colour of a single pixel in a bitmapped image. Higher colour depth gives a broader range of distinct colours. For example, an image stored as .gif file uses 8 bit per pixel so that the image could use 256 different colours.
   • Resolution
     • The number of pixels in an image expressed as: no. pixels across x no. pixels down
   • Metadata
     • Data about data. In the case of image files metadata is the data the computer needs to interpret the image data in the file e.g. resolution, colour depth and image dimensions.

7. Sound

   • Analogue
     • A continuously changing wave such as natural sound.
   • Digital
     • Data that is made up of separate values. How data is stored on a computer.
   • Sample Rate
     • The number of times per second that the sound wave is measured. The higher the rate the more accurately the sound wave is represented.
   • Sample Interval
     • The time gap between measurements of the sound wave being taken. Another way of expressing the sampling rate.
   • Sample Resolution
     • The number of bits used to store the value of each sample. The higher the number of bits the more accurately the value is stored.
   • ADC
     • Analogue to Digital Converter: takes a real-world analogue data and converts it to a binary representation that can be stored on a computer.

8. Data and Information

   • Data
     • Facts and figures with no context or format to give them meaning.
   • Information
     • Processed data that has context and format so that it conveys meaning.

9. Instructions

   • Instruction Set
     • The group of instructions available for that specific processor to use. The number of instructions available will depend on the number of bits used. For example, with 4 bits there could potentially be 15 different instructions.
   • Opcode
     • The group of bits in an instruction that represents the operation such as EAT, MOVE or TURN.
   • Operand
     • The group of bits in an instruction that represents the data
   • Compiler
     • A piece of system software that converts a program written in a high level programming language into machine code (binary).
   • Machine Code
     • A binary representation of a program.
   • High-Level Programming Language

10. CPU

    • CPU
      • The central processing unit that contains the processor, main memory and cache.
    • RAM
      • The memory in the CPU that is used to temporarily store programs while they are running and data used by these programs. The processor fetches instructions from the main memory. Memory is made up of many addressable locations.
    • Processor
      • The component in the computer that fetches, decodes and executes instructions.
    • Cache
      • High speed memory in the CPU that is used to store a copy of frequently used instructions and data. It has a faster access speed than main memory and is used to improve CPU performance.
    • Clock Speed
      • Measured in hertz or cycles per second, the clock speed represents how many instructions per second the processor can execute. The higher the clock speed the faster the CPU can operate.
    • System Buses
      • The circuits/internal wiring that connect the processor and main memory together.
    • Fetch-Execute Cycle
      • The process by which a program is run: instructions are stored in main memory, fetched by the processor one at a time, decoded and executed.
    • Dual/Quad Core
      • A CPU that contains multiple processor components (cores) that can operate independently to process more than one task at a time.

11. Memory

    • RAM
      • Random Access Memory: a type of memory that is read-write and volatile. Used for main memory.
    • ROM
      • Read Only Memory: memory that is hard-coded at the time of manufacture. Stores the start-up programs and the boot-strap loader.
    • Bootstrap Loader
      • The first program that is loaded into main memory from ROM when a computer is switched on. This will load the operating system from secondary storage.
    • Volatile
      • Describes memory that loses its contents when the power is turned off
    • Non-volatile
      • Describes memory that does not lose its contents when the power is turned off
    • Secondary Memory
      • Long term, non-volatile storage media such as hard disks, memory sticks, magnetic tapes and CDs.
    • Virtual Memory
      • Part of the hard disk that is configured to behave as an extension to main memory.
    • Magnetic
      • Secondary storage such as hard disks, tape and floppy disks.
    • Optical
      • Secondary storage that is read using lasers such as CDs and DVDs.
    • Solid State/Flash
      • Memory Secondary storage that has no moving parts. Used in memory sticks, cameras and phones.
    • Pen drive
      • Another term for a USB memory stick.

12. Binary Logic

    • Boolean Expression
      • An expression that is either true or false
    • Truth Table
      • A table that shows all the possible combinations of input and their logical output value.
    • Logical Operator
      • AND,OR,NOT
    • Logic Diagram
      • A diagram of a circuit showing logic gates with inputs and the outputs they generate.

13. Software Categories

    • Software
      • Programs that run on the computer.
    • System Software
      • Programs that are used to run the computer, including the operating system, library routines and programming language translators
    • Application Software
      • Programs that perform a task for a user. This is something that the user would do with or without a computer – it is the task that matters not the computer.
    • Operating System
      • System software that is necessary to run the computer.
    • Library
      • Systems software modules that perform frequently required tasks. They can be built into or called from other programs.
    • Utility Programs
      • System software that provides other useful functions for operating the computer.
    • Translators
      • System software that translates high level programming languages into machine code. Include compilers, interpreters and assemblers.

14. Operating Systems

15. Applications

    • Open Source
      • Software that is provided under licence but free of charge to anyone. The source code is made available and can be modified.
    • License
      • An agreement that defines the conditions for using the software.
    • Freeware
      • Software that is provided free of charge under license but without the source code. It is copyrighted and cannot be modified
    • Proprietary Software
      • Software that is copyrighted and the license is old under a patented or trademarked name.
    • Off-the-Shelf Software
      • Software that can be purchased from a high street or online store as it is
    • Bespoke
      • Software that is written for a customer’s specific requirements

16. Database Concepts

17. Networking

18. Internet

19. Security

20. Compression

21. Algorithms

22. Programming Languages

23. Handling Data in Algorithms

24. Utilities