10 Oct
2005
10 Oct
'05
1:35 a.m.
On Sun, 9 Oct 2005, Chuck Guzis wrote:
On 10/9/2005 at 11:42 AM Vintage Computer Festival
wrote:
You'd have a point if it didn't work so well ;)
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. 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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