Data Representation

Data Representation

1. Units

   • Bit: A single binary digit: 1 or 0
   • Byte: 8 bits
   • Nibble: 4 bits
   • Kilobyte: 1024 bytes
   • Megabyte: 1024 kilobytes
   • Gigabyte: 1024 megabytes
   • Terabyte: 1024 gigabytes

2. Numbers

   • Binary: Base 2 number system, used by computers, uses the digits 1 & 0 only
   • Denary (a.k.a. decimal): Base 10 number system, how we normally count, uses digits 0 to 9
   • Hexadecimal: Base 16 number system used by humans to represent groups of four bits at a time. 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

3. Characters

   • Character sets: The set of symbols that can be represented by a computer. The symbols are called characters and can be letters, digits, space, punctuation marks and some control characters 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

4. Imaging

   • Bitmap image: 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 graphic: An image file that is made up of lines and shapes that have certain properties, for example, a line may have the following properties: 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 bit-mapped image
   • 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 a .gif file uses 8 bits per pixel so the image could use 256 different colours
   • Resolution: The number of pixels in an image expressed as: the-number-of-pixels-across x the-number-of-pixels-down eg: 400 x 600
   • 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, for example: resolution, colour depth and image dimensions

5. 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 real-world analogue data and converts it to a binary representation that can be stored on a computer

6. 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

7. 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
   • Op Code: The group of bits in an instruction that represents the operation such as EAT, MOVE or TURN
   • Compiler: A piece of systems 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: A programming language written in constructs using language we can Programming understand. Languages include Delphi, Visual Basic, Java and C++ Language