AMSDOS Header: Difference between revisions

Revision as of 02:39, 13 January 2021

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:

Size	Name	Notes
BYTE	User number	0-15, or #E5 for deleted entries
8 BYTES	Filename	Unused characters are filled with space
3 BYTES	Extension	Unused characters are filled with space
BYTE	Block number	Tape only
BYTE	Last block	Tape only
BYTE	File type	0:BASIC 1:Protected 2:Binary (ASCII files don't have headers)
WORD	Length	???
WORD	Load address
BYTE	First block	Tape only?
WORD	Logical length	Actual file length is here
WORD	Entry address
36 BYTES	Unused
3 BYTES	Real length	24-bit number. Just a copy, not used!
WORD	Checksum	Unsigned sum of all bytes until this field
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.

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 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:
- Byte 00: User number (value from 0 to 15 or #E5 for deleted entries)
+{| class="wikitable"
- Byte 01 to 08: filename (fill unused char with spaces)
+|-
- Byte 09 to 11: Extension (fill unused char with spaces)
+! Size !! Name !! Notes
- Byte 16: first block (tape only)
+|-
- Byte 17: first block (tape only)
+| BYTE || User number || 0-15, or #E5 for deleted entries
- Byte 18: file type (0:basic 1:protected 2:binary)
+|-
- Byte 21 and 22: loading address LSB first
+| 8 BYTES || Filename || Unused characters are filled with space
- Byte 23: first block (tape only?)
+|-
- Byte 24 and 25: file length LSB first
+| 3 BYTES || Extension || Unused characters are filled with space
- Byte 26 and 27: execution address for machine code program LSB first
+|-
- Byte 64 and 66: 24 bits file length LSB first. Just a copy, not used!
+| BYTE || Block number || Tape only
- Byte 67 and 68: checksum for bytes 00-66 stored LSB first
+|-
- Byte 69 to 127: undefined content, free to use
+| BYTE || Last block || Tape only
+|-
+| BYTE || File type || 0:BASIC 1:Protected 2:Binary (ASCII files don't have headers)
+|-
+| WORD || Length || ???
+|-
+| WORD || Load address ||
+|-
+| BYTE || First block || Tape only?
+|-
+| WORD || Logical length || Actual file length is here
+|-
+| WORD || Entry address ||
+|-
+| 36 BYTES || Unused ||
+|-
+| 3 BYTES || Real length || 24-bit number. Just a copy, not used!
+|-
+| WORD || Checksum || Unsigned sum of all bytes until this field
+|-
+| 59 BYTES || Unused || Free to use
+|}
 To calculate the checksum just add all bytes from 00 up to and including byte 66 together.