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Fixed length records

A file where all the records are of the same length is said to have fixed length records.

Some fields are always the same length (eg Postcode is always 7 characters). Some fields may need to be 'padded out' so they are the correct length 
(eg Surname - If 15 characters are stored then Jenkins would be stored as 'JENKINS        ' - 7 characters followed by 8 spaces).

Advantage : Access is fast because the computer knows where each record starts.

Eg If each record is 120 bytes long then

  • the 1st record starts at [Start of File] + 0 bytes
  • the 2nd record starts at [Start of File] + 120 bytes
  • the 3rd record starts at [Start of File] + 240 bytes etc.....

Disadvantage : Using Fixed length records, the records are usually larger and therefore need more storage space and are slower to transfer (load or save).
 

In the Example

NUMBER SURNAME FORENAME YEAR FORM DOB
92013 JONES Sidney 12 B 23/04/78
92107 LAIDLAW Lorraine 12 Y 12/11/79
92114 MERRITT Mandy 12 G 08/03/79
92167 NASH Natasha 12 B 19/08/78

...the field lengths may be..

Number : 5
Surname: 15
Forename: 15
Year: 2
Form: 1
DOB: 8

Each record would be 46 bytes long.

The first record of the example file would be stored as ...(each box represents one byte of storage)..

9 2 0 1 3 J O N E S                    
S i d n e y                   1 2 B 2 3
/ 0 4 / 7 8