Big Blue chips for Apple eclipse Motorola's G4s

PITY POOR Motorola. No sooner does IBM detail how it's going to wrest the performance crown away from its erstwhile PowerPC partner, courtesy of the Power 4-based 64-bit PowerPC 970, but information leaks out of Motorola showing just how slow its high-performance processor ramp really is.

A presentation made at last July's Smart Networks Developer Forum, Motorola's less-publicised answer to Intel's media-friendly shindig, shows the company's 'desktop' future is centred firmly on its G4 architecture and not the G5, as many observers expected. The G5 exists as a Motorola product class, but for a series of chips aimed at communications and networking applications - not, in other words, likely to turn up in a desktop system any time in the future.

I first learned about this split - G4 for embedded and desktop apps; G5 for embedded and communications roles - last March during a chat with a senior Motorola source. It was one of those 'you didn't hear this from me kind of conversations', but even speaking anonymously, he was sticking to the party line. But he did let slip Motorola's decision to extend the G4 architecture as far as possible and one or two other titbits. He rubbished rumours of a desktop G5.

I'm grateful to Architosh, which first revealed the SMDF information, just before Motorola pulled the offending PDF file from its Web site, for confirming the existence of the desktop-oriented G5 chip, knocked on the head by Motorola or Apple late 2001 or early 2002 - not long after I'd been reporting on its specifications, as leaked by an Apple source late last year.

Architosh's sources and mine agree on most points, but Architosh reveals more about the chip's fate. Codenamed 'Eleven', the G5 went like the proverbial off a shovel, could hit 2.4GHz (with all the heat implications that implies) and made it into Macs distributed to a number of test locations. Those systems, says Architosh, were recalled last February, not long before Mr Motorola told be the "G5 is not the successor to the G4".

Architosh believes Apple and Motorola came to blows over the chip's bus. Motorola wanted RapidIO, Apple wanted to use its new, proprietary bus ApplePI (Processor Interconnect). ApplePI (as revealed by Matthew Rothenberg and Daniel Drew Turner over at eWeek.com) is expected to be used in IBM's PowerPC 970. Like Architosh, I suspect the new bus is based on HyperTransport. Apple is, after all, an HT Consortium member.

The 970 is scheduled to debut mid-2003 at up to 1.8GHz. Motorola isn't likely to hit that kind of clock speed until late 2003/early 2004 at the earliest. According to an internal sales document written in September, the company will ship rev. 3.3 of the current G4, the MPC7455, during late December. The revision drops the 800MHz-1GHz parts' core voltage from 1.6V to 1.3V in the process.

That will have to do until Q2 2003, when Motorola plans to release the 1.3GHz MPC7457. The 7457 doubles the 7455's on-die L2 cache to 512KB, support up to 4MB of backside L3 cache (double the 7455's limit) and ups the maximum frontside bus clock speed to 200MHz. All this is achieved by fabbing the part at 0.13 micron using an eight-layer metal silicon-on-insulator process.

Now, I first heard about the 7457 (as the 7470) earlier this year as a contender for the summer 2002 Power Mac update. We wonder if Apple designed the new Power Macs to take the 1.3GHz chip, and when the 7457 failed to appear, it was forced to overclock the 1GHz 7455 to 1.25GHz.

Beyond the 7457, Motorola's sales document promises a "2GHz+" version of the chip but gives no timeframe (could this be the real owner of the '7470' tag?). Further off is the "G4+" (a codename Motorola has used before, incidentally, for the MPC7450), which will offer "a high level of integration" and... RapidIO. It too is a 0.13 micron SOI part. The G4+ could be a contender for the '7500' moniker, though nothing in the sales PDF confirms that view.

How this will map out for Apple is another matter, but a likely scenario is relegating the Motorola G4 (whatever its number is) to consumer and portable systems and reserving the IBM 970 for pro desktops. µ