Article-I.D.: atari.142
Posted: Tue Mar 18 12:22:11 1986
Date-Received: Sat, 22-Mar-86 05:19:09 EST
References: <8603171654.AA07440@mitre-bedford.ARPA>
Organization: Atari Corp., Sunnyvale CA
Lines: 40


Here is the REAL story of an Atari DOS data sector.  This is taken
verbatim from the Atari OS manual.

----------------

The format of a sector in a user's data file is shown below:

	 7             0
	+-+-+-+-+-+-+-+-+
	|  data		|   +0
	+-+-+-+-+-+-+-+-+
	| file #    |hi |   +125
	+-+-+-+-+-+-+-+-+
	|forward pointer|   +126
	+-+-+-+-+-+-+-+-+
	|S| byte count  |   +127
	+-+-+-+-+-+-+-+-+

The file # is a redundant piece of information which is used to verify
file integrity; the file number field contains the value of the
directory position of that file.  If there is ever a mismatch
between the file's position in the directory and the file number as
contained in each sector, the Disk File Manager will generate the
error $A4.

The forward pointer field contains the ten bit value of the disk sector
number of the next sector of the file.  The pointer will equal zero
for the last sector of the file.

The S bit indicates whether or not the sector is a "short" sector (one
containing fewer than 125 data bytes).  S is equal to one when the
sector is short.

The byte count field contains the number of data bytes in the sector.

----------------


-Landon