Clock Trade-Offs

March 1997 / Reviews / Power Macs: Cookin' at 225 MHz / Clock Trade-Offs

Using Apple motherboard designs with Power Mac ASICs helps guarantee Mac clone compatibility. Most of our test units use Apple's Tsunami motherboard design. It's the only design that allows multiprocessing, but its memory bus operates at lower clock speeds than current Wintel motherboards. Apple's 9500/200 operates its 200-MHz 604e CPU with a clock multiplier of 4 on a 50-MHz memo ry bus. Although memory vendor and accelerator maker Newer Technologies asserts that the Tsunami bus was designed to run at 60 MHz, Apple has not authorized any systems running over 50 MHz.
Power Computing and UMAX run the 225-MHz 604e chip with a clock multiplier of 5 on a 45-MHz bus. This means that t he 11 percent speed increase of the 225-MHz CPU (over a 200-MHz 604e) can be largely offset by the 10 percent speed slowdown on the memory bus. To benefit from the faster CPU, a program must stay off the bus, working largely in the cache.

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Matthew Wilson
My approach to software engineering is far more pragmatic than it is theoretical--and no language better exemplifies this than C++.

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