This memory is produced by either Samsung or Qimonda.ДЄccording to Mark Rein of Epic Games, Microsoft had originally planned on using only 256В MB of RAM, but the decision to increase it was based on Epic's upcoming Gears of War title. The memory is shared by the CPU and the GPU via the unified memory architecture. The console features 512В MB of GDDR3 RAM clocked at 700В MHz with an effective transmission rate of 1.4В GHz on a 128-bit bus. In this specific case of data streaming, called Xbox procedural synthesis (XPS), the CPU is effectively a data decompressor, generating geometry on-the-fly for consumption by the GPU 3D core. The system allows for the GPU to directly read data produced by the CPU without going to main memory. Writes streaming from each core skip the L1 cache, due to its no-write allocation (avoids thrashing of high-bandwidth, transient, write-only data streams on the L1 cache), and goes directly to the L2 cache. There were several types of fan used in Xbox 360s, which were produced by Nidec, Sunon, and Delta Electronics.Дuring read streaming into the CPU, a custom prefetch instruction, extended data cache block touch (xDCBT) prefetches data directly to the L1 data cache of the intended core, which skips putting the data in the L2 cache to avoid thrashing the L2 cache. The heat sink was cooled by two 70В mm fans at the rear of the console on original-style consoles, while a single fan mounted on the side of the consoles was used in Xbox 360 S consoles. Newer revisions, which had a smaller core, do not feature the heat pipe or copper base. The heat sink implemented to cool the Xenon CPU was composed of aluminum fins with a copper base, and a heat pipe. The CPU also contained ROM storing Microsoft private encrypted keys, used to decrypt game data. The write-through data cache did not allocate cache lines on writes. Each core had 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. This cache was shared amongst the three CPU cores. Xenon was equipped with an 8th way set associative 1 MB Level 2 cache on-die running at half CPU clock speed. A 21.6В GB/s front side bus, aggregated 10.8В GB/s upstream and downstream, connected Xenon with the graphics processor/ northbridge. The original chip used a 90В nm process, although a newer 65В nm process SOI revision was implemented on later models, which was in-turn superseded by a 45В nm combined CPU and GPU chip. However, to reduce CPU die size, complexity, cost, and power demands, the processor used 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. Each core of the CPU was capable of simultaneous multithreading and was clocked at 3.2 GHz. This led to an approximate 50 percent savings in required band-width and memory footprint making the CPU having a theoretical peak performance of 115.2 GFLOPS, being capable of 9.6 billion dot products per second. The VMX128 was also modified by the addition of direct 3D (D3D) compressed data format. The dot-product instruction took far less latency than discrete instructions. The SIMD vector processor (VMX128) was modified for the Xbox to include a dot-product instruction. The CPU emphasized high floating point performance through multiple FPU and SIMD vector processors in each core. The XCPU, named Xenon at Microsoft and 'Waternoose' at IBM, is a custom triple-core 64-bit PowerPC-based design by IBM. The Xbox 360 took a different approach to hardware compared to its predecessor.

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