Atari File Management Subsystem - Revision history

Dan Tobias at 15:11, 9 June 2019

2019-06-09T15:11:28Z

Dan Tobias at 15:04, 9 June 2019

2019-06-09T15:04:21Z

Dan Tobias at 21:30, 29 December 2013

2013-12-29T21:30:01Z

Dan Tobias: /* See also */

2013-12-29T18:56:39Z

‎See also

Dan Tobias: /* Links */

2013-12-29T18:56:01Z

‎Links

Dan Tobias: /* Volume table of contents (VTOC) */

2013-03-20T00:08:46Z

‎Volume table of contents (VTOC)

Dan Tobias at 09:03, 18 March 2013

2013-03-18T09:03:51Z

Dan Tobias at 08:52, 18 March 2013

2013-03-18T08:52:51Z

Dan Tobias at 07:21, 18 March 2013

2013-03-18T07:21:49Z

Dan Tobias: /* Boot record */

2013-03-18T07:11:28Z

‎Boot record

@@ Line 19: / Line 19: @@
 * '''Sector 1''': Boot record
-* '''Sector 2-n''': DOS.SYS file (on system disks)
+* '''Sector 2-n''': DOS.SYS file (on system disks; n depends on the size of the file; n=1 on non-system disks so that user space starts with sector 2)
 * '''Sector n+1-359''': User file space
 * '''Sector 360''': VTOC (Volume Table of Contents)
@@ Line 79: / Line 79: @@
 == Links ==
-* [http://archive.org/details/bitsavers_atari40080mputerTechnicalReferenceNotes1982_20170986 Atari technical manual] with lots of tech details
+* [http://archive.org/details/bitsavers_atari40080mputerTechnicalReferenceNotes1982_20170986 Atari technical manual] with lots of tech details (relevant section starts at page 78)
 [[Category:Atari computers]]

@@ Line 2: / Line 2: @@
 |formattype=electronic
 |subcat=Filesystem
 }}
-The '''[[Atari File Management Subsystem]]''' (FMS) is the filesystem on an [[Atari 810]] floppy disk.
+The '''Atari File Management Subsystem''' (FMS) is the filesystem on an [[Atari 810]] floppy disk.
 The 720 sectors of the disk were numbered from 1 to 720, but (perhaps due to poor communication between the different development teams at Atari) the FMS filesystem was designed to support sector addresses in the range from 0 to 719, which meant that sector 720 was not addressable but a nonexistent sector 0 was. This resulted in the filesystem only using the 719 sectors in the overlap between what is addressable and what actually exists, so sector 720 is unused (a waste of a perfectly good 128 bytes).

@@ Line 3: / Line 3: @@
 |subcat=Filesystem
 }}
+The '''[[Atari File Management Subsystem]]''' (FMS) is the filesystem on an [[Atari 810]] floppy disk.
 The '''Atari File Management Subsystem''' (FMS) is the filesystem on an [[Atari 810]] floppy disk.
 The 720 sectors of the disk were numbered from 1 to 720, but (perhaps due to poor communication between the different development teams at Atari) the FMS filesystem was designed to support sector addresses in the range from 0 to 719, which meant that sector 720 was not addressable but a nonexistent sector 0 was. This resulted in the filesystem only using the 719 sectors in the overlap between what is addressable and what actually exists, so sector 720 is unused (a waste of a perfectly good 128 bytes).

← Older revision		Revision as of 18:56, 29 December 2013
Line 75:		Line 75:

	== See also ==		== See also ==
		+	* [[Atari 810]] (physical disk format)
	* [[ATR]] (disk image file)		* [[ATR]] (disk image file)

← Older revision		Revision as of 18:56, 29 December 2013
Line 73:		Line 73:

	Byte 127 uses its high bit to indicate a "short sector" (one not entirely filled with data), setting it to 1 if it is such a sector. The remaining bits indicate the number of data bytes stored in this sector.		Byte 127 uses its high bit to indicate a "short sector" (one not entirely filled with data), setting it to 1 if it is such a sector. The remaining bits indicate the number of data bytes stored in this sector.
		+
		+	== See also ==
		+	* [[ATR]] (disk image file)

	== Links ==		== Links ==

@@ Line 51: / Line 51: @@
 * '''Byte 0''': Directory type (always 0)
 * '''Byte 1-2''': Maximum sector number (always 02C5, which is incorrect given that this equals 709 and the actual maximum sector number used by the FMS is 719. Due to this error, this value is ignored.)
-* '''Byte 3-4''': Number of sectors available (starts at 719 and changes as sectors are allocated or deallocated)
+* '''Byte 3-4''': Number of sectors available (starts at 709 and changes as sectors are allocated or deallocated)
 * '''Byte 10-99''': Bitmap showing allocation of sectors. The high-order bit of byte 10 corresponds to (the nonexistent) sector 0 (so it is unused), the next-lower bit corresponds to sector 1, and so on through sector 7 for the low-order bit of byte 10, then sector 8 for the high-order bit of byte 11, and so on. These are set to 1 if the sector is available, and 0 if it is in use.

@@ Line 12: / Line 12: @@
 The bytes within a sector are numbered from 0 to 127, because at least the development teams managed to agree on zero-based numbering there.
-Multi-byte numbers in these formats are [[Endianness|little-endian]].
+Multi-byte numbers in these formats are [[Endianness|little-endian]] (except for a special case noted below).
 == Sector map ==
@@ Line 65: / Line 65: @@
 Filenames are similar to [[MS-DOS]] and [[CP/M]] in that they consist of (up to) 8 characters in the main filename plus an extension of up to 3 characters.
 == Links ==

@@ Line 42: / Line 42: @@
 * '''Byte 16-17''': DOS.SYS starting sector number
 * '''Byte 18-127''': Code for second phase of boot
 == Links ==

@@ Line 28: / Line 28: @@
 Sector 1 is the boot record. It has this structure:
-* ''Byte 0'': 0 (representing boot flag)
+* '''Byte 0''': 0 (representing boot flag)
-* ''Byte 1'': 1 (representing the number of sectors the boot record takes)
+* '''Byte 1''': 1 (representing the number of sectors the boot record takes)
-* ''Byte 2-3'': Boot address (0700)
+* '''Byte 2-3''': Boot address (0700)
-* ''Byte 4-5'': Init address
+* '''Byte 4-5''': Init address
-* ''Byte 6'': 4B (JMP command used with address in following 2 bytes)
+* '''Byte 6''': 4B (JMP command used with address in following 2 bytes)
-* ''Byte 7-8'': Boot read continuation address
+* '''Byte 7-8''': Boot read continuation address
-* ''Byte 9'': Max # of files open concurrently (1-8)
+* '''Byte 9''': Max # of files open concurrently (1-8)
-* ''Byte 10'': Specific drive numbers supported (bitmap where low-order bit means drive 1, next bit drive 2, and so on up to 4)
+* '''Byte 10''': Specific drive numbers supported (bitmap where low-order bit means drive 1, next bit drive 2, and so on up to 4)
-* ''Byte 11'': Buffer allocation direction (set to 0)
+* '''Byte 11''': Buffer allocation direction (set to 0)
-* ''Byte 12-13'': Boot image end address + 1
+* '''Byte 12-13''': Boot image end address + 1
-* ''Byte 14'': Boot flag (must be nonzero if DOS.SYS is on disk)
+* '''Byte 14''': Boot flag (must be nonzero if DOS.SYS is on disk)
-* ''Byte 15'': Sector count (not used)
+* '''Byte 15''': Sector count (not used)
-* ''Byte 16-17'': DOS.SYS starting sector number
+* '''Byte 16-17''': DOS.SYS starting sector number
-* ''Byte 18-127'': Code for second phase of boot
+* '''Byte 18-127''': Code for second phase of boot
 == Links ==