The CPU in the Xbox was a custom Pentium III running at 733MHz. The 'custom' part of this was that the Pentium III in the Xbox only had a 128KB L2 cache instead of the usual 256KB. This allowed Microsoft to buy them at a bit of a discount and Intel to shift a few more CPUs.
- Mobile Intel® Celeron® Processor (0.18μ) in BGA2 and Micro-PGA2 Packages This datasheet is for the mobile version Coppermine with 256kB L2 cache. It does not contain the Xbox Coppermine-128 with 128kB L2 cache at 733MHz (S-Spec SL5SN). No such datasheet exists. Both differences are pin compatible.
- Mobile Intel® Celeron® Processor (0.18μ and 0.13μ) Specification Update This document should contain the errata for the Xbox CPU.
- Wikipedia - List of Intel Pentium III microprocessors: "Coppermine" (180 nm)
- CPU upgrading adapter for a Microsoft XboxTM game machine US Patent Application 20050282621 by Friendtech, filed 2003-08-21.