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3c305e8a37
* Update documentation (note apple flux writing is a unicorn now even though this isn't quite true until #489) * Fix DOS 3.3 mapping * Add ProDOS (all versions) mapping
74 lines
2.4 KiB
Markdown
74 lines
2.4 KiB
Markdown
Disk: Apple II
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==============
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Apple II disks are nominally fairly sensible 40-track, single-sided, 256
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bytes-per-sector jobs. However, they come in two varieties: DOS 3.3/ProDOS and
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above, and pre-DOS 3.3. They use different GCR encoding systems, dubbed
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6-and-2 and 5-and-3, and are mutually incompatible (although in some rare
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cases you can mix 6-and-2 and 5-and-3 sectors on the same disk).
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The difference is in the drive controller; the 6-and-2 controller is capable
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of a more efficient encoding, and can fit 16 sectors on a track, storing
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140kB on a disk. The 5-and-3 controller can only fit 13, with a mere 114kB.
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Both formats use GCR (in different varieties) in a nice, simple grid of
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sectors, unlike the Macintosh. Like the Macintosh, there's a crazy encoding
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scheme applied to the data before it goes down on disk to speed up
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checksumming.
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In addition, a lot of the behaviour of the drive was handled in software.
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This means that Apple II disks can do all kinds of weird things, including
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having spiral tracks! Copy protection for the Apple II was even madder than
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on other systems.
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FluxEngine can only read well-behaved 6-and-2 disks. It doesn't even try to
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handle the weird stuff.
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Apple DOS also applies logical sector remapping on top of the physical sector
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numbering on the disk, and this _varies_ depending on what the disk is for.
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FluxEngine can remap the sectors from physical to logical using modifiers. If
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you don't specify a remapping modifier, you get the sectors in the order they
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appear on the disk.
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Reading discs
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-------------
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Just do:
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```
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fluxengine read apple2
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```
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You should end up with an `apple2.img` which is 143360 bytes long.
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It will be in physical sector ordering. You can specify a sector ordering,
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`appledos` or `prodos` to get an image intended for use in an emulator,
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due to the logical sector mapping issue described above:
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```
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fluxengine read apple2 prodos
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```
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Writing discs
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-------------
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Just do:
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```
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fluxengine write apple2 -i apple2.img
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```
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If your image is in logical sector ordering (images intended for emulators
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usually are), specify a modifier of `appledos` or `prodos`:
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```
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fluxengine write apple2 prodos -i apple2.img
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```
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Useful references
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-----------------
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- [Beneath Apple DOS](https://fabiensanglard.net/fd_proxy/prince_of_persia/Beneath%20Apple%20DOS.pdf)
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- [MAME's ap2_dsk.cpp file](https://github.com/mamedev/mame/blob/4263a71e64377db11392c458b580c5ae83556bc7/src/lib/formats/ap2_dsk.cpp)
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