Fixed length
- Every single record is exactly the same size
- You have to know in advance how many characters will be assigned to a field
- ✅ It is easy to determine where to read a record, as you know exactly how many spaces each field takes us
- Lots of whitespaces - wasted storage ❌
- Used for postcode/national insurance number
Variable length
- Only the actual data input is stored - used in both serial and sequential files
- No whitespace ✅
- Can’t go directly to read a record ❌
- Used for address, personal statement etc.