On Jul 23, 4:21 pm, Gregg Eshelman <[email protected]> wrote:
> It's fairly easy to overclock a 100 mhz Turbo 601 but
> the 66 Mhz must have some parts relocated and some
> other parts added. It's easy to hack OS 8.6 to run on
> a Turbo 601 (or the 601 upgrades for 040 macs), but
> last I looked hacking 9.x wasn't fully figured out.
Both upgrade cards use a bus speed of 33 MHz. The 66 MHz card
doubles the 33 MHz bus speed to the 66 MHz CPU speed. The 100 MHz
card triples the 33 MHz bus speed to the 100 MHz CPU speed.
Apparently, the PPC601 does not include internal support for clock
tripling. So an external clock buffer/multiplier chip is used on the
100 MHz version. This chip, the ICS9178 is what must be added to the
66 MHz version to upgrade it to a 100 MHz version. There were also a
few resistors to add and remove.
The ICS9178 was also used on the 100 MHz version of the 8100 and
clones. It is now out of production, although ICS might still
produce a pin compatible chip which serves the same function.
On later clock-tripling PPC601 machines, the 7200, Apple used a
Motorola clock buffer/multiplier.
Probably not terribly useful information, but someone might be
curious. As far as I know, I'm the only person to successfully
convert the 66 MHz card to 100 MHz and it actually topped out at about
96 MHz. I eventually sold the upgraded card to a fellow in, IIRC,
Germany.
The Turbo601 upgrade for the IIci was kind of like a dancing bear.
The amazing thing wasn't that it danced so well, the amazing thing was
that it danced at all.
Jeff Walther
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