Assessing performance not a simple matter of clock speeds

Choosing the highest-performance computer based on the latest PowerPC processors from IBM and Motorola isn't as easy as selecting the one with the highest clock speed, according to Microprocessor Report.

Recently the PowerPC team boosted the performance of the 604e to 350MHz, the fastest PowerPC CPU yet. The PowerPC duo also offers the PowerPC 750 processor at a slower 266MHz, but it has a second bus that, like the dual-independent bus of Intel's P6, allows higher-speed access to Level 2 cache, explained Linley Gwennap, publisher and editor in chief of Microprocessor Report.

As a result, the two CPUs produce better results on different tests, Gwennap said.

The 604e is about 20 per cent faster than a 300MHz Pentium II in either integer or float-ing-point operations, Gwennap noted. "We're going to be able to do things that flat-out can't be done on the Intel architecture," said Will Swearingen, manager of PowerPC product marketing for Motorola.

However, it is the 750 that shines in real-world applications, Gwennap said.

Forward looking

The 750 "was optimised for Macintosh", Gwennap said. "The difference is the extra bandwidth of the 750's backside cache bus."

"We've spent time looking at Mac code in order to optimise it for the Mac platform," said Lori Peterson, manager of PowerPC product marketing for IBM Microelectronics.

The Somerset Design Centre of the Apple-IBM-Motorola alliance, in Austin, Texas, can be reached or