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PowerPC G5 performance ‘stunning’ – sources

But it won't come cheaply

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Motorola's PowerPC 8500 - aka the G5 - continues to move steadily toward its scheduled release, our Apple sources tell us.

The G5 is the next major version of the PowerPC architecture and includes a new internal bus structure, a longer, ten-stage instruction pipeline, redesigned integer and floating-point maths units. It will be offered in 32-bit and 64-bit versions, and fabbed using silicon-on-insulator technology at 0.13 micron

That said, it may still require active cooling - at 1.4GHz, the processor draws 26W, which is quite a bit in PowerPC terms. The current PowerPC 7450 draws up to 17W at 533MHz.

Two major problems have been hampering the company's efforts to get the chip into upcoming Power Macs: issues with the clock multiplier and cache coherency glitches. The former has been fixed with the G5's latest revision, version 0.5, we hear.

Says our source: "What this problem meant is that a few chips ran at full speed, and others only ran at 601 [ie. the first generation of PowerPC processor, circa 1994] speeds or below at an equivalent MHz, and most chips did not work at all. This new revision has brought a 16-fold increase in yields, and those chips that do function all function the same at an equivalent clock speed."

Initial benchmarks supplied by our source suggest the G5 is pretty fast indeed:

GHz 1.2 1.4 1.6
SpecInt2000 987 1151 1340
SpecFP2000 1005 1173 1359

By comparison, Intel's 2GHz Pentium 4 has recorded SpecInt2000 and SpecFP2000 scores of 656 and 714, respectively, according to

www.specbench.org

If accurate, the G5 figures are impressive indeed.



Meanwhile, the cache problem, now found to be the result of two separate bugs, one effecting the integrity of data held in the cache and the other relating to the part's multiprocessing features. Both, say our source, are set to be fixed with the next revision, version 0.6, due early next month.

When the chip finally ships, it won't be cheap. Our source quotes $575 for a 1.2GHz part and $695 for the 1.6GHz version, but that may change depending on final yields of the product. It's worth noting that these prices are not much more than the kind of price Intel charges for new CPUs. ®

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