[Info-vax] OT: For MAC Lovers Only :-)

[glen herrmannsfeldt]

JF Mezei <jfmezei.spamnot at vaxination.ca> wrote:

(snip on floppy disk formats, then I wrote)

>> The drives convert transitions (0 to 1 or 1 to 0) into magnetic
>> flux reversals, and the opposite on read. (At least for the
>> usual floppy drives and ST506 style hard drives.) All the
>> timing is done by the controller, including precompensation.

> But surely the controller would have come from Sony ?

Not usually. The original IBM PC used one from NEC that is
similar to one from Intel. Later x86 machines used something
related to those, sometimes integrated into a larger custom
control chip.

As for Apple, the Apple II disk controller is mostly implemented
using a simple state machine built with small ROMs, called
the Woz Machine. No fancy PLL data separator to lock onto
the bits and figure out where the clock and where the data
bits are. In GCR there are no separate clock and data bits.

For the first Mac, a custom IC was built, called the IWM or
Integrated Woz Machine. 

Later, when HD disks became popular, Apple introduced the
Super drive that could read/write both formats, and the SWIM
(some combination of Super, Woz, Integrated, and Machine, though
the actual acronym varies).

-- glen