Xenon (processor)

Xenon is a CPU that is used in the Xbox 360 game console. The processor, internally codenamed "Waternoose", which was named after Henry J. Waternoose III in Monsters Inc. by IBM^[1] and XCPU by Microsoft, is based on IBM PowerPC instruction set architecture, consisting of three independent processor cores on a single die. These cores are slightly modified versions of the PPE in the Cell processor used on the PlayStation 3.^[2][3] Each core has two symmetric hardware threads (SMT), for a total of six hardware threads available to games. Each individual core also includes 32 KiB of L1 instruction cache and 32 KiB of L1 data cache.

The processors are labelled "XCPU" on the packaging and are manufactured by Chartered (now part of GlobalFoundries). Chartered reduced the fabrication process in 2007 to 65 nm, thus reducing manufacturing costs for Microsoft.

The name "Xenon" was repurposed from the code name for the Xbox 360 in early development.

Specifications

• 90 nm process,^[4] 65 nm process upgrade in 2007^[5] (codenamed "Falcon", later "Jasper"), 45 nm process since Xbox 360 S model^[6]
• 165 million transistors
• Three symmetrical cores, each two way SMT-capable and clocked at 3.2 GHz^[4]
• SIMD: VMX128 with 2× (128×128 bit) register files for each core^[4]
• 1 MB L2 cache^[4] (lockable by the GPU) running at half-speed (1.6 GHz) with a 256-bit bus
• 51.2 gigabytes per second of L2 memory bandwidth (256 bit × 1600 MHz)
• 21.6 GB/s front-side bus^[4]
• Dot product performance: 9.6 billion per second
• Restricted to in-order code execution^[4]
• eFuse 768 bits^[7]
• ROM (and 64 kbytes SRAM) storing Microsoft's Secure Bootloader, and encryption hypervisor^[7]
• Big endian architecture

XCGPU

The Xbox 360 S introduced the XCGPU, which integrated the Xenon CPU and the Xenos GPU onto the same die, and the eDRAM into the same package. The XCGPU follows the trend started with the integrated EE+GS in PlayStation 2 Slimline, combining CPU, GPU, memory controllers and IO in a single cost-reduced chip. It also contains a "front side bus replacement block" that connects the CPU and GPU internally in exactly the same manner as the front side bus would have done when the CPU and GPU were separate chips, so that the XCGPU doesn't change the hardware characteristics of the Xbox 360.

XCGPU contains 372 million transistors and is manufactured by Advanced Technology Investment Company and AMD's GlobalFoundries on a 45 nm process. Compared to the original chipset in the Xbox 360 the combined power requirements are reduced by 60% and the physical chip area by 50%.^[8][9]

References

• Xenon hardware overview by Pete Isensee, Development Lead, Xbox Advanced Technology Group, written some time before 23 June 2007

External links

• Ars Technica explains the Xenon CPU