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2.6 Data representation


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Bit
A single binary digit: 0 or 1
Byte
8 bits
Nibble
4 bits
Kilobyte
1024 bytes
Megabyte
1024 kilobytes
Gigabyte
1024 megabytes
Terabyte
1024 gigabytes
Binary
Base 2 number system, used by computers, uses the digits 0 & 1 only.
Denary
Base 10 number system, how we normally count, uses digits 0 to 9.
Hexadecimal (hex)
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.
Character Set
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.
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 Image
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.
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.
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.
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 understand. Languages include Delphi, Visual Basic, Java and C++.