Re: Apple ][ plus 13 sector! Problems...

[Dan Foster <usenet@evilphb.org>]

In article <20040719171427.04872.00000146@mb-m12.aol.com>, Michael J. Mahon <mjmahon@aol.com> wrote:
>
> Although Mossberg does a nice job of disassembling DOS and
> explaining its logic, the definitive work on the low-level encoding
> and the state machine that decodes it is undoubtedly Sather's
> "Understanding the Apple II" and "Understanding the Apple //e".

Ahh! Thanks for the pointer. I'll have to see about finding a copy.

> Unfortunately, Mr. Irwin also misunderstands both the actual
> magnetic encoding on the disk and the way that DOS converts
> data bytes to "disk nibbles" for writing.
>
> Making the same error as the early editions of "Beneath Apple
> DOS", Irwin says that all bits are written to disk interleaved
> with clock pulses.  This is false.
>
> Apple's (Wozniak's) GCR scheme was designed precisely to
> _avoid_ having to use clock bits, thereby increasing the data
> capacity of a track by 50%.

Ahhhh. Ouch, that's a big technical blooper on Mr. Irwin's part, then.
:(

-Dan