CP/M on an Apple II ?

[Vintage Computer Festival]

On Sun, 9 Oct 2005, Chuck Guzis wrote:

> On 10/9/2005 at 11:42 AM Vintage Computer Festival wrote:
>
> >This is over-stated quite grandly.  The Apple ][ disk system was
> >extremely reliable.  And it still is.  My 20 year old disks still read and
> >write just fine.
>
> Overstated or not, an 8 bit simple arithmetic checksum to guard 256
> (actually 410) data bytes is pretty weak.

You'd have a point if it didn't work so well ;)

> On more than one occasion, not a hint of an error flag was raised when a
> bad sector was read. I noted that the corrupted data had the same
> checksum as what the correct data woiuld have had.

With only an 8-bit checksum it is entirely possible this can happen, but
in all my vast experience working on the Apple ][ I have never (knowingly)
come across this problem.  When doing data recovery on Apple ][ disks, you
normally want to disable checksum checking anyway so that you can see what
the DOS is reading and then try to recover.

But as far as the Disk ][ controller and GCR encoding goes, don't equate
simple with shoddy: it is an extremely robust system.

-- 

Sellam Ismail                                        Vintage Computer Festival
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International Man of Intrigue and Danger                http://www.vintage.org

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