Progress on NEC APC

From: Fred Cisin <>
Date: Fri Apr 21 16:05:55 2000

On Fri, 21 Apr 2000, Dwight Elvey wrote:
> . . . I don't think is is a MS-DOS disk
> either. The FAT and such take up a lot of space and
> surely wouldn't return "NO FILE" if CP/M tried to read it.

In THIS case, I take it back, but because the NEC 8" CP/M disks that I've
seen used 256 bytes per sctor.

Although the FAT and such take up a lot of space, it's not THAT much, and
CP/M skips some tracks. A typical 8" (or 1.2M 5.25") MS-DOS uses 1/2K for
the boot sector, 2 copies of the FAT at 3.5K each, and 7K for the
DIRectory sectors. That is all done with by the end of the second side of
the first cylinder (#0). On double density CP/M 8", the directory hardly
ever starts before the first side of the second (#1) cylinder. Plus, the
latter parts (unused if the disk isn't full) of the MS-DOS DIRectory
sectors could be misinterpreted by CP/M as an empty directory.
Therefore, it's possible (although somewhat demented - BTDT) to actually
have two different DIRectory structures that access the same files in
order to create a distribution disk that is readable by multiple OS's!

BTW, MS-DOS CAN have reserved tracks, but I can't remember anyone other
than DEC Rainbow doing so.
BTW2, MS-DOS uses the sectors in consecutive order, CP/M often does not.
BTW3, MS-DOS uses both the second head of the cylinder before stepping to
the next cylinder. Many CP/M formats use all tracks of the first head
before using the second head.

> I think the first step is to try the STAT command as was
> suggested by someone else. That will at least tell you
> if space was reserved for any data by the CP/M OS.

Since the info reported by STAT is based on what it sees in the DIRectory
sectors, it would be based on the same wrong source data, and the NO FILE
diskette would be reported as empty.

> It is still possible that someone used the disk to
> write directly to sectors. There is a program called
> VIEW or something that allows direct sector viewing.
> That might be a good thing to try.

That would be great. But we'd need to get a copy onto Sellam's APC.
Does DDT86 have a read sector command?

Fred Cisin            
2210 Sixth St.                  (510) 644-9366
Berkeley, CA 94710-2219
Received on Fri Apr 21 2000 - 16:05:55 BST

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