View source for AMSDOS Header

In [[AMSDOS]] it is possible to store files in two ways: headerless and with a header. Headerless files are often files which were created with [[OPENOUT]] and ''SAVE"filename",a''. Programs normally have a file header, which consist of 128 bytes and contain the following data:

{| class="wikitable"
|-
! Offset !! Size !! Name !! Notes
|-
| 0 || BYTE || User number || 0-15, or #E5 for deleted entries
|-
| 1 || 8 BYTES || Filename || Unused characters are filled with space
|-
| 9 || 3 BYTES || Extension || Unused characters are filled with space
|-
| C || DWORD || Zero || Contains all zeroes
|-
| 10 || BYTE || Block number || Tape only
|-
| 11 || BYTE || Last block || Tape only
|-
| 12 || BYTE || File type || 0:BASIC 1:Protected 2:Binary (ASCII files don't have headers but a fake header is built in memory with the file type #16, "Unprotected ASCII v1")
|-
| 13 || WORD || Data location || Address of the 2KB buffer
|-
| 15 || WORD ||Load address || 
|-
| 16 || BYTE || First block || Set to #FF, only used for output files
|-
| 17 || WORD ||style="white-space: nowrap;"|  Logical length || Actual file length is here
|-
| 19 || WORD || Entry address || 
|-
| 1B || 36 BYTES || Unused || 
|-
| 3F || 3 BYTES || Real length || 24-bit number. Just a copy, not used!
|-
| 42 || WORD || Checksum || Unsigned sum of all bytes until this field
|-
| 44 || 59 BYTES || Unused || Free to use
|}

To calculate the checksum just add all bytes from 00 up to and including byte 66 together.

This is only a summary. All details are in [[Firmware Guide]] chapter 9, page 4.

[[Category:Disc Operating System]]
[[Category:Programming]]