Cell's Power Processor Element: Cool enough for a laptop?

In the last Cell article, we quoted the 4 Watt spec for the Synergistic Processing Element (SPE) in Cell at 4 GHz, which means 32 Watts if one considers all 8 SPEs. However, one of the big questions for Mac users is the power dissipation of the remainder of the chip, most specifically the Power Processor Element (PPE), since it is this portion of the chip that could be most readily used in a Mac.

The RealWorldTech article suggests that at 4 GHz, the entire chip requires somewhere between 50 and 80 Watts. However, if the Sony PlayStation 3 really will use Cell with most of those SPEs at near 4 GHz, then one would expect the 4 GHz Cell's power dissipation to be closer to the 50 W estimate, since heat dissipation is a big concern for a console. This would also go along with the rumours that suggest that the PPE x 3 is similar to what will appear in Xenon, the chip destined for Microsoft's Xbox 2. A (lower clocked) three-core CPU based off the PPE would make for a chip appropriate for a console, but only if the PPE unit were relatively low power. The Electronic Design article gives a more specific estimate of approximately 60 Watts for the entire chip. If this estimate is close to accurate, it would suggest that Cell at 4 GHz without the SPE units would come in at under 30 Watts, which is perfect for laptop use.

What is unknown is how IBM's PowerPC 970FX (or some other unreleased 9xx series chip) is doing in terms of power utilization. IBM has hinted that they could hit the sub-30 Watt window with a G5 chip clocked at 1.9 GHz or less.

So what will Apple use in their next PowerBook? That is of course still unknown to us. However, while I do think it's most likely that Apple's future PowerBooks will sport a G5 variant, it is nice to see that there are several possible options:

1) IBM G5 970FX 1.8 GHz (with 512 KB L2) or 970GX (with 1 MB L2).
2) Freescale G4 7448 1.8 GHz (with 1 MB L2).
3) IBM Cell PPE 3.5-4.0 GHz (with or without integrated memory controller)
4) Freescale e600 1.8 GHz with integrated memory controller

The potential low power PowerPC options for Apple haven't looked this good for quite some time.