[Simh] C64 and C128

[Ethan Dicks]

On Tue, Jun 30, 2015 at 7:46 PM, Kevin Handy <khandy21yo at gmail.com> wrote:
> The C64 did not run cp/m out of the box, because it did not have any kind of
> Intel 8080 based processor. You could buy a cartridge (iirc) that would
> allow you to run cp/m, but it was basically bolting a cp/m machine onto the
> side of the C64.

There was a C-64 CP/M cartridge.  It was apparently awful.  I never
knew anyone that ever bought one (contrasted with several people I
know that ran CP/M on a card in their Apple II).

The C-64 CP/M card was announced, advertised on the outside of the
C-64 box, then later, engineered and sold mostly to avoid FTC action
for false advertising.

Some Info:

http://www.zimmers.net/cbmpics/xother3.html
http://www.z80.eu/c64.html

> The C128 had both the C64 processor, and a Z80 processor built in, and it
> could run cp/m.

It did, and I've heard Bil Herd's excellent stories about what it took
to make it all work.  I'm pretty sure you can look them up on YouTube
if you haven't had the chance to hear about them in person at a
VCFeast.

> The floppy drive speed was really lousy though (300 baud
> serial bus iirc).

It was a little faster than that... the IEC bus was a sync serial bus
with the CPU doing the bit-banging (due to a well-known (now) hardware
bug with the 6522 VIA shift register used in the 1540 drive and the
VIC-20, or else the IEC bus would have been bytes from the CPU shifted
in/out bit-serial by hardware and several times faster).

Actual throughput was something close to 500 bytes/sec or about 4000
bps.  It took a little over 2 minutes to read 64Kbytes of data.  This
is still much slower than all the other (non-IEC) machines of the day.

Commodore did fix things up later with the C-128 and 1571 and 1581
drives with a "fast serial" interface that did use hardware features
of the 6526 CIA (found in the C-64 but not used to its potential).
There's a lot of history behind the story of these interfaces, but
those are some of the high points.

-ethan