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52 lines
2.0 KiB
Markdown
52 lines
2.0 KiB
Markdown
Disk: Commodore 64
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==================
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Commodore 64 disks come in two varieties: GCR, which are the overwhelming
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majority; and MFM, only used on the 1571 and 1581. The latter were (as far as
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I can tell) standard IBM PC format disks, so use `fluxengine read ibm` to
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read them (and then [let me know if it
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worked](https://github.com/davidgiven/fluxengine/issues/new).
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The GCR disks are much more interesting. They could store 170kB on a
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single-sided disk (although later drives were double-sided), using a proprietary
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encoding and record scheme; like [Apple Macintosh disks](macintosh.md) they
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stored varying numbers of sectors per track to make the most of the physical
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disk area, although unlike them they did it by changing the bitrate rather than
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adjusting the motor speed.
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The drives were also intelligent and ran DOS on a CPU inside them. The
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computer itself knew nothing about file systems. You could even upload
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programs onto the drive and run them there, allowing all sorts of custom disk
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formats, although this was mostly used to compensate for the [cripplingly
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slow connection to the
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computer](https://ilesj.wordpress.com/2014/05/14/1541-why-so-complicated/) of
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300 bytes per second (!). (The drive itself could transfer data reasonably
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quickly.)
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A standard 1541 disk has 35 tracks of 17 to 21 sectors, each 256 bytes long.
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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 c64
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```
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You should end up with an `c64.d64` file which is 174848 bytes long. You can
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load this straight into a Commodore 64 emulator such as
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[VICE](http://vice-emu.sourceforge.net/).
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**Big warning!** Commodore 64 disk images are
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complicated due to the way the tracks are different sizes and the odd sector
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size, so you need the special D64 or LDBS output formats to represent them
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sensibly. Don't use IMG unless you know what you're doing.
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Useful references
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-----------------
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- [Ruud's Commodore Site: 1541](http://www.baltissen.org/newhtm/1541c.htm):
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documentation on the 1541 disk format.
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