In an attempt to offer the most powerful game console on the planet and ensure that the PlayStation 3 games are unique, Sony decided to put a very advanced Cell processor inside the machine. But now it transpires that to produce the chip in large quantities is not that easy.
IBM’s vice president of semiconductor and technology services said during an interview that with big chips like the Cell processor, jointly developed by IBM, Sony and Toshiba, 10% – 20% yields are normal and the chipmakers should be lucky enough to get such output of fully functional chips. But the Cell microprocessors are to be used in Sony PlayStation 3, which will sell in millions, which means that a question about Sony’s ability to ship the console in quantities rises.
“[Defects] become a bigger problem the bigger the chip is. With chips that are one-by-one and silicon germanium, we can get yields of 95%. With a chip like the Cell processor, you’re lucky to get 10 or 20%. If you put logic redundancy on it, you can double that,” said Tom Reeves, VP of semiconductor and technology services at IBM, in an interview with Electronic News web-site.
The Cell microprocessor incorporates one dual-threaded PowerPC core and eight so-called synergistic processing engines (SPEs) intended for floating-point calculations, the most demanding tasks in entertainment, workstation and server systems. The PowerPC core is projected to have 32KB L1 cache and 512KB L2 cache, while each of the SPEs will have 256KB of cache. The Cell has built-in Rambus XDR memory interface, capable of data rates from 3.20GHz to 8.0GHz. The chip also uses FlexIO processor buses that are capable of running at up to 6.40GHz.
Given that there are many SPEs inside the Cell, which can go malfunction, while the rest of chip will operate fine, the Cell chip can be utilized in applications, where all eight SPEs are not required. For example, Sony PlayStation 3 game console requires Cell processors with seven synergistic processing units. The yield of Cell processor with seven SPEs is unclear, but IBM claims there is sufficient amount of Cell chips with only six synergetic processing units.
“There are a lot of chips with six cores operational, and we’ve been thinking about whether we should really throw all of those away. We also have a separate part number for chips with all eight cores good. The stuff that’s going to be for medical imaging, aerospace and defense and data uses eight cores,” Mr. Reeves said.
It is not the first time when the Cell processor accused of low yields. Recently it was reported that Sony may lower clock-speed of the Cell processor in the console to 2.80GHz, down from 3.50GHz expected initially, due to low yields at high clock-speeds. Meanwhile, according to Merrill Lynch research company, the Cell processor will cost Sony “at least” $230 per unit to make, another indicator of low yields.