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Re: DSK format specification
- Subject: Re: DSK format specification
- From: pausch@saaf.se (Paul Schlyter)
- Date: Sun, 13 Jul 2003 08:58:07 +0000 (UTC)
- Newsgroups: comp.emulators.apple2, comp.sys.apple2, comp.sys.apple2.comm, comp.sys.apple2.programmer
- Organization: Svensk Amat|rAstronomisk F|rening
- References: <rLOPa.250$Y%3.201@nwrddc03.gnilink.net> <lr0Qa.1241$dk4.53908@typhoon.sonic.net> <jr4Qa.16082$C07.14264@nwrddc02.gnilink.net> <OU7Qa.1395$dk4.59598@typhoon.sonic.net>
- Xref: archiver1.google.com comp.emulators.apple2:3638 comp.sys.apple2:32806 comp.sys.apple2.comm:439 comp.sys.apple2.programmer:2211
In article <OU7Qa.1395$dk4.59598@typhoon.sonic.net>,
Andy McFadden <fadden@fadden.com> wrote:
>
>The trouble with ".DSK" images is that they were either written as a
>series of 256-byte sectors (sector 0, 1, 2, 3, ...) or a series of 512-byte
>ProDOS/Pascal blocks (sector 0, 2, 4, 6, ...).
...and of course a Pascal 512-byte block was mapped into two 256-byte
sectors....
In CP/M, there was a further mapping done, into the 128-byte logical
sectors used by CP/M. Naturally two 128-byte CP/M sectors was mapped
into one 256-byte Apple sector. Nevertheless, CP/M had TWO levels
of sector interleave: one specificed within CP/M itself and executed
by Z80 code (it existed in all CP/M implementations), and another within
the BIOS code of Apple CP/M and executed by 6502 code; the latter was
Apple II specific.
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