Amiga double density disk - Revision history

Limi: The Amiga 4000 did indeed come with HD floppy drives (at 1.76MB formatted capacity). See e.g. amigahistory.plus.com.

2020-03-19T00:53:57Z

The Amiga 4000 did indeed come with HD floppy drives (at 1.76MB formatted capacity). See e.g. amigahistory.plus.com.

Kyz at 16:01, 10 December 2016

2016-12-10T16:01:06Z

Kyz at 15:43, 10 December 2016

2016-12-10T15:43:43Z

Kyz at 14:48, 10 December 2016

2016-12-10T14:48:21Z

Kyz at 14:38, 10 December 2016

2016-12-10T14:38:39Z

Kyz at 14:32, 10 December 2016

2016-12-10T14:32:03Z

Kyz at 14:23, 10 December 2016

2016-12-10T14:23:08Z

Kyz at 14:21, 10 December 2016

2016-12-10T14:21:47Z

Kyz at 14:16, 10 December 2016

2016-12-10T14:16:44Z

Kyz at 14:16, 10 December 2016

2016-12-10T14:16:04Z

@@ Line 9: / Line 9: @@
 Because of the Amiga's more flexible control over the floppy disk, the Amiga could read most other physical disk formats, including the [[PC-DOS 720K format|PC disks]], [[Apple double-density 3 1/2" disk|Apple disks]] and even Commodore 64 and Apple 5¼" disks with a suitable external disk drive.
-No Amiga model ever came with a high-density drive. However, the Amiga did support them, and high-density drives were available from third party vendors. The [[Amiga high density disk]] format is the same as the double disk format, but with 22 sectors per track instead of 11.
+Only the Amiga 4000 ever came with a built-in high-density drive. High-density drives were also available from third party vendors. The [[Amiga high density disk]] format is the same as the double disk format, but with 22 sectors per track instead of 11.
 Disks were generally formatted with with one of the Amiga's standard filesystems: [[OFS]] (Old File System) natively supported by AmigaOS 1.0-1.2, or [[FFS]] (Fast File System) supported by AmigaOS 1.3 and higher. However, other filesystems could be used, including [[PFS]] (Professional File System), [[AFS]] (Ami File Safe) and [[SFS (Amiga)|SFS]] (Smart File System). The Amiga could read PC disks formatted with the [[FAT12]] filesystem using third party software called CrossDOS. Commodore licensed CrossDOS from its authors and bundled it with Workbench 2.1 and higher.

@@ Line 7: / Line 7: @@
 The Amiga uses an MFM sync word to mark the start of sectors (0x4489, a special MFM-encoding of the byte 0xA1, so it can be distinguished from normal 0xA1 bytes which would be MFM-encoded as 0x44A9). This contrasts with the [[PC-DOS 720K format]] which used the floppy disk index hole and careful timing to determine where sectors were located. Amiga disks were typically read or written as entire tracks at once, rather than reading individual sectors. Sectors could be in any order on a track; each sector had a header with its track and sector number.
-Because of the Amiga's more flexible control over the floppy disk, the Amiga could read most other physical disk formats, including the [[PC-DOS 720K format|PC disks]], [[Apple double-density 3 1/2" disk|Apple disks]] and, with an suitable external disk drive, even Commodore 64 and Apple 5¼" disks.
+Because of the Amiga's more flexible control over the floppy disk, the Amiga could read most other physical disk formats, including the [[PC-DOS 720K format|PC disks]], [[Apple double-density 3 1/2" disk|Apple disks]] and even Commodore 64 and Apple 5¼" disks with a suitable external disk drive.
 No Amiga model ever came with a high-density drive. However, the Amiga did support them, and high-density drives were available from third party vendors. The [[Amiga high density disk]] format is the same as the double disk format, but with 22 sectors per track instead of 11.

@@ Line 11: / Line 11: @@
 No Amiga model ever came with a high-density drive. However, the Amiga did support them, and high-density drives were available from third party vendors. The [[Amiga high density disk]] format is the same as the double disk format, but with 22 sectors per track instead of 11.
-Disks were generally formatted with with one of the Amiga's standard filesystems: [[OFS]] (Old File System) natively supported by Workbench 1.0-1.2, or [[FFS]] (Fast File System) supported by Workbench 1.3 and higher. However, other filesystems could be used, including [[PFS]] (Professional File System), [[AFS]] (Ami File Safe) and [[SFS (Amiga)|SFS]] (Smart File System). The Amiga could read PC disks formatted with the [[FAT12]] filesystem using third party software called CrossDOS. Commodore licensed CrossDOS from its authors and bundled it with Workbench 2.1 and higher.
+Disks were generally formatted with with one of the Amiga's standard filesystems: [[OFS]] (Old File System) natively supported by AmigaOS 1.0-1.2, or [[FFS]] (Fast File System) supported by AmigaOS 1.3 and higher. However, other filesystems could be used, including [[PFS]] (Professional File System), [[AFS]] (Ami File Safe) and [[SFS (Amiga)|SFS]] (Smart File System). The Amiga could read PC disks formatted with the [[FAT12]] filesystem using third party software called CrossDOS. Commodore licensed CrossDOS from its authors and bundled it with Workbench 2.1 and higher.
 The Amiga operating system provided raw access to floppy disks via a driver called <tt>trackdisk.device</tt>. It was possible to squeeze even more onto double-density disks; Klaus Deppisch's <tt>diskspare.device</tt> allowed 12 sectors instead of 11, and, for drives that supported it and disks that had flux material that far in, 82 tracks instead of the standard 80, in total allowing 984KiB instead of the standard 880KiB.

@@ Line 11: / Line 11: @@
 No Amiga model ever came with a high-density drive. However, the Amiga did support them, and high-density drives were available from third party vendors. The [[Amiga high density disk]] format is the same as the double disk format, but with 22 sectors per track instead of 11.
-Disks were generally formatted with with one of the Amiga's standard filesystems: [[OFS]] (Old File System) natively supported by Workbench 1.x, or [[FFS]] (Fast File System) supported by Workbench 2.x and higher. However, other filesystems could be used, including [[PFS]] (Professional File System), [[AFS]] (Ami File Safe) and [[SFS (Amiga)|SFS]] (Smart File System). The Amiga could read PC disks formatted with the [[FAT12]] filesystem using third party software called CrossDOS. Commodore licensed CrossDOS from its authors and bundled it with Workbench 2.1 and higher.
+Disks were generally formatted with with one of the Amiga's standard filesystems: [[OFS]] (Old File System) natively supported by Workbench 1.0-1.2, or [[FFS]] (Fast File System) supported by Workbench 1.3 and higher. However, other filesystems could be used, including [[PFS]] (Professional File System), [[AFS]] (Ami File Safe) and [[SFS (Amiga)|SFS]] (Smart File System). The Amiga could read PC disks formatted with the [[FAT12]] filesystem using third party software called CrossDOS. Commodore licensed CrossDOS from its authors and bundled it with Workbench 2.1 and higher.
 The Amiga operating system provided raw access to floppy disks via a driver called <tt>trackdisk.device</tt>. It was possible to squeeze even more onto double-density disks; Klaus Deppisch's <tt>diskspare.device</tt> allowed 12 sectors instead of 11, and, for drives that supported it and disks that had flux material that far in, 82 tracks instead of the standard 80, in total allowing 984KiB instead of the standard 880KiB.

@@ Line 5: / Line 5: @@
 The '''Amiga double density disk format''' (3 1/2", double sided, double density) was the standard format for disks on all Amiga models. It had 80 tracks per side, 11 sectors per track, and 512 bytes per sector. Data was stored with [[MFM encoding]].
-Unlike the [[PC-DOS 720K format]], the Amiga did not use the index hole and careful timing to determine where sectors were located. Synchronization words were used instead: 4489 4489 (the MFM-encoded form of bytes A1 A1). Amiga disks were typically read or written as entire tracks at once, rather than reading individual sectors. Sectors could be in any order on a track.
+The Amiga uses an MFM sync word to mark the start of sectors (0x4489, a special MFM-encoding of the byte 0xA1, so it can be distinguished from normal 0xA1 bytes which would be MFM-encoded as 0x44A9). This contrasts with the [[PC-DOS 720K format]] which used the floppy disk index hole and careful timing to determine where sectors were located. Amiga disks were typically read or written as entire tracks at once, rather than reading individual sectors. Sectors could be in any order on a track; each sector had a header with its track and sector number.
 Because of the Amiga's more flexible control over the floppy disk, the Amiga could read most other physical disk formats, including the [[PC-DOS 720K format|PC disks]], [[Apple double-density 3 1/2" disk|Apple disks]] and, with an suitable external disk drive, even Commodore 64 and Apple 5¼" disks.

@@ Line 3: / Line 3: @@
 |subcat=Floppy disk
 }}
-The ''Amiga double density disk format''' (3 1/2", double sided, double density) was the standard format for disks on all Amiga models. It had 80 tracks per side, 11 sectors per track, and 512 bytes per sector. Data was stored with [[MFM encoding]].
+The '''Amiga double density disk format''' (3 1/2", double sided, double density) was the standard format for disks on all Amiga models. It had 80 tracks per side, 11 sectors per track, and 512 bytes per sector. Data was stored with [[MFM encoding]].
 Unlike the [[PC-DOS 720K format]], the Amiga did not use the index hole and careful timing to determine where sectors were located. Synchronization words were used instead: 4489 4489 (the MFM-encoded form of bytes A1 A1). Amiga disks were typically read or written as entire tracks at once, rather than reading individual sectors. Sectors could be in any order on a track.