14 DAY TRIAL // Intel's Pat Gelsinger stated in a recent interview with the German tech site heise.de that the original Pentium core design had been used as the base of the processor cores featured by Intel's forthcoming Larrabee GPU. Larrabee proves to be a bunch of P54C Pentium cores, pre-MMX, which make the foundation of a new, flexible x86-based GPU, after having been put together and enhanced with wider vector floating-point resources.
It seems that Intel did not use P55 with MMX as a base for its Larrabee, and chose the older P54C, due to some involvement from the Pentagon. At least, this is what Ars Technica's Jon Stokes sustains.
The story is very simple, says Stokes. After abandoning Pentium for becoming obsolete, Intel offered the RTL code for the processor to the Pentagon to be used in military applications, since the means to fabricate a radiation hardened version of the processor already existed. Like other technology of its kind, Pentium brought a real advantage as it had been intensively tested and debugged. The military were able to get it made on low-volume since they had their own fabrication facilities. What the military began producing was a rad-hard model of the chip, after the P54C's RTL code had been cleaned up by the Pentagon.
As history repeats itself, when the P54C was abandoned by the Pentagon, the RTL was offered back to Intel. The company had little to do next, since the core had been thoroughly debugged, and only modified it to become the many-core chip we know as Larrabee.
As for the performance capabilities of the forthcoming Larrabee, Intel is said to have claimed an upcoming SIGGRAPH paper that the GPU will bring 20 times more performance per watt than a Core 2 Duo and half the single-threaded performance of Core 2 Duo. The chip also features three-operand vector instructions and a 4MB coherent L2.
That's about all Stokes was able to reveal, and no specific information of what the "half the single-threaded performance" means or the type of workload Intel uses for the performance figure has been made public. It seems that, if looking at Pentium's pipeline, which is less than half the depth of Core 2's, and considering the GPU in the 1.7GHz to 2.5GHz range, it is better than Core 2. The workload is the major variable when comparing the short pipeline of Larrabee and the long one of Core 2.