CP/M on an Apple II ?

[Chuck Guzis]

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.  

To be completely fair, my experience was wth some fairly mangled Apple ][ diskettes.  Fortunately, they contained mainly ASCII text, so picking up errors "by eye" was simple.    The number of errors per diskette was very large, but when you're doing data recovery, you've got what you've got.   You read as much of the diskette as possible and save the good sectors in one pile and try to whittle away the size of the bad sector pile using various tricks in your toolkit.

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.

Let's face it, most diskettes, even those 20 years old would fare just fine with a read-and-compare after write and NO checksum of any kind.  It's that small minority with errors that makes one nervous.

Cheers,
Chuck