PENT PRO CPUS

8/29/98

Pentium Pro CPU: the Pentium Pro was introduced in Nov of 1995. It differed from the Pentium by having substantially improved parallelism and instruction look ahead in its dual processing units. It also incorporated a 256k or optional 512K Level 2 cache packaged with the CPU. The internal L2 cache was on a separate physical chip in the package, but offered much more favorable timing than motherboard L2 caches. The floating point performance was enhanced by improving pipelining and removing some stack handling delays. Packaging was a 387 pin grid array. Power consumption for the 150MHz CPU was somewhat in excess of 20 watts

The Pentium Pro suffered from two substantial problems. First, the production costs of the integrated L2 cache did not drop at the usual rate for single chip designs. The Pentium Pro started expensive, as top of the line CPUs always do. But the price did not drop as rapidly over time as single chip CPU designs did. More important, the Pentium Pro parallel processing/instruction lookahead was inhibited when 8 or 16 bit subsets of registers were referenced. The result was that the Pentium Pro often executed older "Legacy Code" little, if any, faster than a cheaper Pentium of the same clock speed did. Intel's benchmarks show a Pentium Pro to be about 40% faster than a Pentium at the same clock speed. That is possibly valid for pure 32 bit code. Intel also claims a Pentium Pro executes three instructions per clock cycle, but that appears to be a maximum rate that is unsustainable except possibly by carefully designed benchmarks.

The Pentium Pro was introduced as a 150MHz/166MHz CPU and was later released at 180 and 200MHz ratings. A 200MHz version with a 1024K integrated L2 cache was also released. A 333MHz Pentium Pro override CPU for Socket 8 (Pentium-Pro) motherboards was released in September 1998.

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