Central Processing Unit
The Xbox 360 takes a new approach to hardware compared to its predecessor. The XCPU, named Xenon at Microsoft and "Waternoose" at IBM, is a custom triple-core 64-bit PowerPC-based design by IBM. The CPU emphasizes high floating point performance through multiple FPU and SIMD vector processors in each core. The SIMD vector processor (VMX128) was modified for the Xbox to include a dot-product instruction. The dot-product instruction takes far less latency than discrete instructions. The VMX128 was also modified by the addition of direct 3D (D3D) compressed data format. This led to an approximate 50 percent savings in required band-width and memory footprint. It has a theoretical peak performance of 115.2 gigaFLOPS and is capable of 9.6 billion dot products per second. Each core of the CPU is capable of simultaneous multithreading and is clocked at 3.2 GHz. However, to reduce CPU die size, complexity, cost, and power demands, the processor uses in-order execution in contrast to the Intel Coppermine 128-based Pentium III used in the original Xbox, which used more complex out of order execution. The original chip used a 90 nm process, although a newer 65 nm process SOI revision was implemented on later models, which was in-turn superseded by a 45 nm combined CPU and GPU chip. A 21.6 GB/s front side bus, aggregated 10.8 GB/s upstream and downstream, connected Xenon with the graphics processor/northbridge. Xenon was equipped with a 8th way set associative 1 MB Level 2 cache on-die running at half CPU clock speed. This cache is shared amongst the three CPU cores. Each core has separate L1 caches, each containing a two-way set associative 32-Kbyte L1 instruction cache and a four-way set associative 32-Kbyte L1 data cache. The write-through data cache does not allocate cache lines on writes. The CPU also contains ROM storing Microsoft private encrypted keys, used to decrypt game data. The heat sink implemented to cool the Xenon CPU is composed of aluminum fins with a copper base, and a heat pipe. Newer revisions, which have a smaller core, do away with the heat pipe and copper base however. The heat sink is cooled by two 70 mm fans at the rear of the console on original-style consoles, while a single fan mounted on the side of the consoles is used in Xbox 360 S consoles. There are several types of fan used in Xbox 360s, which are produced by Nidec, Sunon and Delta Electronics.
Read more about this topic: Xbox 360 Hardware
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