Attached Link: http://developer.intel.com/design/PentiumIII/prodbref/

You are mistaken. Check the link. For the socket370 PentiumIII: 32k level1 cache 256k level2 cache On-die, running at core speed. I still can't find any PIII motherboards with onboard cache memory, and have never seen mention of them. Your suggested figures for this alleged motherboard cache (512mb - 1.5Gb) leads me to believe you are confused with normal RAM. The only Intel processors with extra cache are the Xeon versions of the PII and PIII. The 4-way and 8-way versions come with up to 2 megabytes of Level2 cache, but it is on the processor, not the motherboard.