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IBM preps 1GHz-plus PowerPC 750GX ‘Gobi’

Successor to 750FX due this summer

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Further details have emerged about IBM's next revision of its G3-class processor family, codenamed Gobi, but set to ship as the PowerPC 750GX. It will finally take the G3 family to 1GHz and beyond.

The chip is the successor to IBM's current top-end G3 CPU, the 750FX. That part, launched in October 2001, was due to ship in January 2002 and scale from 600MHz to 1GHz. The 1GHz version was expected to arrive late 2002.

Well, it's now May 2003, and there's still no sign of the 1GHz 750FX. According to industry sources, it's never going to get there. Instead, sources familiar with IBM's plans told us, it will offer a new processor, the 750GX.

IBM inadvertently mentioned the as yet unannounced 750GX is a document published last January. The PDF details "power supply routing, bypassing and layout considerations" for the PowerPC 740 and 750 chips. But it notes that "other bypassing considerations apply to the PowerPC 750CXe, 750FX and 750GX processors".

No spec. information is given - the PDF merely acknowledges the existence of the 750GX. Sources cited by Think Secret late last year and by MacEdition early this year simply recorded the part's existence and that it would ship in volume in Q1 2003.

Our sources suggest the part will indeed ship at 1GHz and beyond. However, the part has yet to sample - though this is likely to happen "soon", with volume shipments commencing in the "summer".

Full spec. information remains scarce, but we understand that like the 750FX, codenamed Sahara, the 750FX will operate across a 200MHz frontside bus and has been designed to be pin-compatible with the older chip. Both chips contain 64KB of L1 cache (32KB each for data and instructions), but while the 750FX contains 512KB of on-die L2 cache, the 750GX will contain 1MB.

The key difference between the two parts, however, is that that the 750GX will be fabbed at a smaller process than the 0.13 micron 750FX - most likely 0.10 micron.

"They tried to get to 1GHz with the FX but they couldn't get there. They had to wait until they could so a die-shrink," we were told. A die-shrink would certainly allow IBM to double the part's L2 cache and increase the clock frequency without increasing its heat generation and power consumption profiles by too great a margin - essential for an embedded processor, which is what the G3 family effectively is, these days.

Precise specs., particularly how high the 750GX will clock, remain uncertain but we were told that the 1MB on-die L2 cache is "a definite".

An unverified comment posted on Mac Rumors.com suggests that the part will ship at up to 1.4GHz, but the unknown poster claims the part will ship in the autumn. Our source said "summer", you'll recall, but 1.4GHz sounds right, even if it's a figure plucked out of the air.

The 750GX's own successor, codenamed Mojave, but possibly officially monikered the 750VX is said by Mac Rumors.com's poster to be due to sample late 2003 at 1.5GHz and up. It will be a G3-class CPU incorporating Motorola's AltiVec SIMD technology. IBM has already said it will use AltiVec in its upcoming 64-bit PowerPC 970.

MacEdition's mole claimed it would also be fabbed at 0.10 micron, but kick off at 1.6GHz. Unlike the current 750, it will be designed for multi-processing.

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