mirror of
https://github.com/davidgiven/fluxengine.git
synced 2025-10-31 11:17:01 -07:00
53 lines
2.0 KiB
Markdown
53 lines
2.0 KiB
Markdown
Disk: Commodore 64
|
|
==================
|
|
|
|
Commodore 64 disks come in two varieties: GCR, which are the overwhelming
|
|
majority; and MFM, only used on the 1571 and 1581. The latter were (as far as
|
|
I can tell) standard IBM PC format disks, so use `fluxengine read ibm` to
|
|
read them (and then [let me know if it
|
|
worked](https://github.com/davidgiven/fluxengine/issues/new).
|
|
|
|
The GCR disks are much more interesting. They could store 170kB on a
|
|
single-sided disk (although later drives were double-sided), using a proprietary
|
|
encoding and record scheme; like [Apple Macintosh disks](macintosh.md) they
|
|
stored varying numbers of sectors per track to make the most of the physical
|
|
disk area, although unlike them they did it by changing the bitrate rather than
|
|
adjusting the motor speed.
|
|
|
|
The drives were also intelligent and ran DOS on a CPU inside them. The
|
|
computer itself knew nothing about file systems. You could even upload
|
|
programs onto the drive and run them there, allowing all sorts of custom disk
|
|
formats, although this was mostly used to compensate for the [cripplingly
|
|
slow connection to the
|
|
computer](https://ilesj.wordpress.com/2014/05/14/1541-why-so-complicated/) of
|
|
300 bytes per second (!). (The drive itself could transfer data reasonably
|
|
quickly.)
|
|
|
|
A standard 1541 disk has 35 tracks of 17 to 20 sectors, each 256 bytes long.
|
|
|
|
Reading discs
|
|
-------------
|
|
|
|
Just do:
|
|
|
|
```
|
|
fluxengine read c64
|
|
```
|
|
|
|
You should end up with an `c64.img` which is 187136 bytes long (for a normal
|
|
1541 disk).
|
|
|
|
**Big warning!** The image may not work in an emulator. Commodore 64 disk images are
|
|
complicated due to the way the tracks are different sizes and the odd sector
|
|
size. FluxEngine chooses to store them in a simple 256 x 20 x 35 layout,
|
|
with holes where missing sectors should be. This was easiest. If anyone can
|
|
suggest a better way, please [get in
|
|
touch](https://github.com/davidgiven/fluxengine/issues/new).
|
|
|
|
Useful references
|
|
-----------------
|
|
|
|
- [Ruud's Commodore Site: 1541](http://www.baltissen.org/newhtm/1541c.htm):
|
|
documentation on the 1541 disk format.
|
|
|