26 Jan
2010
26 Jan
'10
11:25 a.m.
On 1/26/10, Jim Brain <brain at jbrain.com> wrote:
On 1/26/2010 12:54 PM, Ethan Dicks wrote:
Most likely. That is a slick design - saves on expensive dual-port memory.
There were tricks one could perform with the 6502
since it had
alternating fetch and execute cycles, so by doing something else with
the bus during the right portion of the clock phase, you could design
a board to "do twice as much" at 1Mhz, but I don't think the 1541 did
that.
He's probably thinking of the earlier IEEE drives. Peddle designed them
and tried to be very clever in the design. They contained a 6502 and
6504 that shared the bus by running one on a (effectively) reversed
clock. THe 6502 got the bus for half a cycle, followed by the 6504, etc. The 1541 (and some of the later IEEE drives) proved
you didn't need that
level of sophistication to operate a floppy disk mechanism.
There was also only a single drive mechanism to fiddle with in the
1541. Design improvements aside, that may have helped shrink it down
to a single processor.
It cost Peddle, too, Jack was furious at the cost and
design lag of the
IEEE drives. I'm not sure Chuck ever fully recovered.
One thing I do remember is the story that some "damn connector" was in
short supply in the PET era and that part of the mandate from Jack was
that the next drive "better not use that".
I never heard for certain which exact connector it was - could have
been the IEEE-488 cable connector or the PCB connector - either way,
no cables or no boards means lost sales opportunities.
-ethan