A Level CS (9618) 13 Data Representation

13.1 User-defined data types 13.2 File organisation and access 13.3 Floating-point numbers, representation and manipulation

User-defined data type

"a data type based on an existing data type or other data types that have been defined by a programmer."

Non-composite data type

"a data type that does not reference any other data types."

Enumerated data type

"a non-composite data type defined by a given list of all possible values that has an implied order."

Pointer data type

"a non-composite data type that uses the memory address of where the data is stored."

Set

"a given list of unordered elements that can use set theory operations such as intersection and union."

Serial file organisation

"a method of file organisation in which records of data are physically stored in a file

Sequential file organisation

"a method of file organisation in which records of data are physically stored in a file

Random file organisation

"a method of file organisation in which records of data are physically stored in a file in any available position; the location of any record in the file is found by using a hashing algorithm on the key field of a record."

Hashing algorithm (file access)

"a mathematical formula used to perform a calculation on the key field of the record; the result of the calculation gives the address where the record should be found."

File access

"the method used to physically find a record in the file."

Sequential access

"a method of file access in which records are searched one after another from the physical start of the file until the required record is found."

Direct access

"a method of file access in which a record can be physically found in a file without physically reading other records."

Mantissa

"the fractional part of a floating point number."

Exponent

"the power of 2 that the mantissa (fractional part) is raised to in a floating-point number."

Binary floating-point number

"a binary number written in the form M × 2E (where M is the mantissa and E is the exponent)."

Normalisation (floating-point)

"a method to improve the precision of binary floating-point numbers; positive numbers should be in the format 0.1 and negative numbers in the format 1.0."

Overflow

"the result of carrying out a calculation which produces a value too large for the computer's allocated word size."

Underflow

"the result of carrying out a calculation which produces a value too small for the computer's allocated word size."