Memory
The Xbox 360 uses 512 MB of DRAM. This is the main system memory which is controlled by Graphics Processing Unit (GPU). The Xbox 360 also contains 700Mhz Graphic-double-data-rate-3(GDDR3) which operates at 1.4 Gbit/pin/s and provides a total main memory bandwidth of 22.4 Gbytes/s. The GPU also includes 10 Mbytes of embedded DRAM (EDRAM), which runs at 256 Gbytes/s for reliable frame and z-buffer bandwidth.
There are two memory controllers incorporated within the system. These 128-byte interleaved GDDR3 memory controllers contain aggressive address tiling for graphics and a fast path to minimize CPU latency.
Cache
The three identical CPU cores share an 8-way set-associative, 1-Mbyte L2 cache and run at 3.2 GHz. Each core contains a complement of
four-way single-instruction, multiple data (SIMD) vector units. The CPU L2 cache, cores, and vector units are customized for Xbox 360 game and 3D graphics workloads. For data streaming, the Xbox 360 contains 128-byte cache line sizes in all the CPU L1 and L2 caches. Larger cache line sizes increase FSB and memory efficiency. The L2 includes a cache-set-locking functionality, common in embedded systems but not in PCs.
Bus
The front-side bus (FSB) runs at 5.4 Gbit/pin/s, with 16 logical pins in each direction, giving a 10.8-Gbyte/s read and a 10.8-Gbyte/s write bandwidth. The bus design and the CPU L2 provide added support that allows the GPU to read directly from the CPU L2 cache. The Bus interface unit interfaces to the FSB handles CPU-initiated transactions, as well as GPU-initiated transactions such as snoops and L2 cache reads. Another type of bus inside the system is the High-speed I/O bus. This bus between the graphics core and the EDRAM die is a chip-to-chip bus (via substrate) operating at 1.8 GHz and 28.8 Gbytes/s. When multisample antialiasing is used, only pixel center data and coverage information is transferred and then expanded on the EDRAM die.
