Transwarp
is an illustrative case:
Quote:
AE released the TransWarp GS in the winter of 1988. The board came stock at 7MHz and 8k cache. They also offered an upgraded board to 8MHz and 32k cache board. The limiting factor to speed at the time was the "buggy" 816 CPU die. Later Western Design Center (WDC) worked with Sanyo to redesign the die, and the CPU speeds easily reached 10MHz. By this time however AE was out of business.
More about Sanyo's assistance in this late 1992 article, helpfully linked by paulb in
this discussion over on Stardot:
"Breaking the 10Mhz barrier", Andrew Roughan, Apple Users' Group, Sydney, Australia.
Quote:
Hot news travels fast these days, and seemingly none travels faster than the news of "14Mhz" 65C816 chips.
...
The chips in question originated from Sanyo who re-engineered the 65C816 to boost its performance. The Sanyo chips run at higher speeds without needing higher voltages or cooling systems.
...
Zip Technology offered an upgrade for a short time and now list a 14Mhz Zip GSX card.
The gist is that WDC have some '816 parts which can run faster than 7MHz, and will supply on request for $95 plus shipping. Although some parts will run at 14MHz it's not clear if any parts are marked that way or if that's any kind of specified timing. Indeed, apparently WDC insisted on first sending some user group notes on how to upgrade you accelerator before selling you a chip:
Quote:
The National AppleWorks Users Group (NAUG) publication 'AppleWorks Forum' has three articles containing very detailed, accurate and informative information written by John Link. The issues are March, April and May 1991. These three issues are considered 'must read' material and are supplied by WDC to any prospective TWGS upgrader. When you contact WDC to purchase a 65C816 chip, they will insist on sending this document (by fax or mail) before processing your order.
The linked article also advises on purchasing faster GALs, cache, and crystal. It mentions crystals from 32MHz to 60MHz, corresponding to 8MHz to 15MHz for the '816.
It also advises on increasing the power supply to 5.5 or even 5.6 volts. Clearly we're in the territory of experimentation and seeing what works, not the territory of works-to-spec. Five examples are quoted for people's results, ranging from 11.5MHz to 14MHz.