The Xbox 360 Central Processing Unit

The CPU for the Xbox 360 is a custom triple-core PowerPC-based design by IBM, known as 'Xenon' at Microsoft and as 'Waternoose' at IBM. The central processing unit emphasises high floating point performance through multiple FPU and SIMD vector processing units in each core, with a theoretical peak performance of 115.2 gigaflops and 9.6 billion dot products per second.

Xenon is equipped with a 1 MiB Level 2 cache on-die running at half CPU clock speed. This cache is shared amongst the three CPU cores. The chip also contains ROM storing Microsoft private encrypted keys, which are used to decrypt game data.

Each core of the CPU is clocked at 3.2 GHz and is capable of simultaneous multithreading. Rather than using the Intel Coppermine128-based Mobile Celeron seen in the original Xbox which used advanced out-of-order execution, this processor uses in-order execution in order to reduce CPU die complexity, cost, size and power demands.

The original chip seen in the Xbox 360 uses a 90 nm process, although a 65 nm process SOI revision is planned for mid-2007. A 21.6 GB/s front side bus, aggregated 10.8 GB/s upstream and downstream, connects Xenon with the graphics processor/northbridge.

The heat sink that operates to cool the CPU is composed of aluminium fins with copper base heat pipes. The heat sink is cooled by two 60 mm fans at the back of the console.