Progress on NEC APC

From: Fred Cisin <>
Date: Fri Apr 21 16:35:10 2000

On Fri, 21 Apr 2000, Don Maslin wrote:
> > what the CP/M-86 would see on the MS-DOS format.
> It gives you a big fat error message.

In THIS case, due to sector size differences. But not ALWAYS. I have
seen non-CP/M disks with E5 where a CP/M directory would have been.

MS-DOS will give a big FAT :-) error message when trying to read CP/M
(actually "Probable Non-DOS disk") because it is picky about what it
expects to see in the F.A.T.

Due to reserved tracks, on 8" double density, CP/M's DIRectory will
fall AFTER the end of the MS-DOS directory, where the first file would
otherwise be likely to be. You're right that that would almost certainly
be content that would choke CP/M. But with very short files and large
clusters, and with sector interleave, it is entirely possible to have CP/M
looking at unused sectors.

Both MS-DOS and CP/M will accept and assume "empty" when encountering
a DIRectory (not the MS-DOS F.A.T.) sector of all E5. MOST MS-DOS formats
fill the empty directory sectors with 00, but not all. Some use E5, some
F6 with E5 every 32 bytes, ... What would CP/M-86 report for a directory
sector of all 00? An MS-DOS format with a large directory could easily
leave the END of the MS-DOS directory sectors where the first of the CP/M
directory sectors would be.

I don't often see use of USER in CP/M disks. Sometimes, but not often. I
think that it is more likely that they gave Sellam blank formatted

Fred Cisin            
2210 Sixth St.                  (510) 644-9366
Berkeley, CA 94710-2219
Received on Fri Apr 21 2000 - 16:35:10 BST

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