New 65nm IBM Cell CPU Promises 19% Power Reduction

While AMD and Intel have been using die size and lithography as measures of finesse and production power against one another -- a measure where smaller is better -- IBM stayed largely out of the foray up to now, making a conscious choice to keep its Cell BE CPU at 90nm while the x86 producers move on to 65nm, and soon 45nm.

IBM's reasons at the time had something to do with leakage: As some theorized, the way Cell's processing engines were designed, current leakage could impact reliability for the symmetric processing units if they were made any smaller.

But now IBM has solved that problem, yesterday announcing that it has officially begun production of the 65nm version of the revolutionary successor to the Power CPU, which now powers some BladeCenter servers and, of course, Sony's PlayStation 3. The way IBM went about this solution was a novel approach, as the company itself shamelessly admitted.

Smaller CPUs must use lower power because electric current tends to leak through their dielectric material - the stuff that guides electrons around like charged marbles in a frantic maze. But when you reduce the voltage, you increase the likelihood of a phenomenon called scatter, where the current gets noisy and unmanageable. So lower voltage isn't something that designers achieve; instead, it's something they have to deal with when smaller sizes are concerned, and make workable.

The method IBM worked out involves two voltage lines rather than just one, the higher of the two is reserved for the "cell" (lower-case "c," which is analogous to AMD's or Intel's "core"), incoming data, and preparation; the lower is used for data being written from the cell and the main read/write circuit.

It's not the first dual-voltage CPU, but how IBM allocates functions among the two voltage lines is new: IBM increases the power to the cell, improving its stability. But then it attaches the write line to that same higher-voltage line, improving the reliability of the key factor that is most susceptible to the scatter effect.


A photographic overview of the components of IBM's 65 nm edition of the Cell CPU A photographic overview of the components of IBM's 65 nm edition of the Cell CPU. (Courtesy IBM)

By increasing the voltage to the cell-specific power line by 200mV over that of the standard power line, the stability of the cell is increased and scatter is reduced. But power consumption is still reduced as a whole, partly because the other functions are running on less voltage, but also because certain parts of the Cell CPU architecture no longer have to stay "on" to mask or counteract the effects of current leakage from the densely-packed processing cells. So overall power consumption, IBM estimates, is reduced by as much as 19%.

An IBM spokesperson declined to comment to BetaNews today regarding whether the company's implementation of the 65nm process for Cell has changed its price.

Most individuals will be introduced to the new CPU by way of the PS3, though Sony recently has had to rework some or all of its latest models, omitting the Emotion engine chip that was the heart of the PS2, and that provided downward compatibility for the newer console, presumably for cost-cutting reasons.

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