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The original XCPU, Waternoose
IntroducedLate 2005
Designed byIBM
Used InOriginal Xbox 360
Clock speed3.2GHz
CacheL1: 32KB/32KB
L2: 1MB
Instruction setPowerPC RISC

The Microsoft XCPU, codenamed Xenon, is the central processor used in the Xbox 360. It is designed to be used with the ATi Xenos graphics chip, which also functions as the northbridge and memory controller.

The processor was developed by Microsoft and IBM, and the first version was codenamed Waternoose after the fictional character Henry J. Waternoose III.


  • 3 two-way SMD-capable RISC cores clocked at 3.2GHz
  • SIMD: Two VMX128 units
  • 32KB L1 data cache
  • 32KB L1 instruction cache
  • 1MB L2 cache at 1.6 GHz with a 256-bit bus
  • 21.6GB/s FSB
  • 768 bits of IBM eFUSE one-time-program memory
  • ROM and 64KB SRAM for storing the 1BL
  • Big-endian architecture


Waternoose (90nm)

The initial versions of the XCPU, known as Waternoose, entered production in 2005 and are used on the Xenon and Zephyr motherboards. It is notable for being quite power hungry.

Loki (65nm)

In 2007, the XCPU was shrunk and slightly redesigned for the 65nm process. Known as Loki, it is used on the Falcon and Jasper motherboards. It is notable for having significantly lower power and thermal requirements.

XCGPU (45nm)

In 2010, the XCPU was shrunk to the 45nm process and combined with the Xenos graphics chip to create a system-on-a-chip, called the XCGPU.