Xenon (processor)
| Company type | Microprocessor |
|---|---|
| Industry | Semiconductor |
| Founded | November 3, 2003 |
| Founder | Microsoft, IBM |
| Headquarters | East Fishkill, Singapore , United States, Singapore |
| Products | Xbox 360 main processor |
Microsoft XCPU, known by the codename Xenon, serves as the main processor within the Xbox 360 system, working alongside ATI's Xenos graphics processing unit.
This CPU was a collaborative development effort between Microsoft and IBM under the IBM initiative titled "Waternoose," named after Henry J. Waternoose III, a character from Monsters, Inc.. The project was publicly revealed on November 3, 2003.
Built upon IBM's PowerPC architecture, the processor incorporates three customized cores inspired by the PPE core found in the PlayStation 3. Each core supports dual symmetric hardware threads (SMT), enabling a total of six threads, and is equipped with separate 32 KB L1 caches for instructions and data.
Production was carried out at IBM’s East Fishkill facility and Chartered Semiconductor Manufacturing (currently part of GlobalFoundries) located in Singapore. In 2007, Chartered shifted fabrication from a 90 nm to a 65 nm process, leading to cost efficiencies for Microsoft.
Specifications
- Initially fabricated using a 90 nm process, later transitioned to 65 nm technology in 2007 (referred to as "Loki"), followed by a 45 nm process with the Xbox 360 S revision, and finally reduced to 32 nm with the Winchester edition
- Integrates approximately 165 million transistors
- Comprises three cores running at 3.2 GHz, each supporting two-way simultaneous multithreading (SMT)
- Contains two VMX128 SIMD units per core—one assigned per thread—with dedicated register files sized at 128×128 bits
- Features an L2 cache of 1 MB that can be locked by the GPU, operating at 1.6 GHz on a 256-bit bus
- Offers an L2 cache memory bandwidth of 51.2 GB/s alongside a front-side bus bandwidth of 21.6 GB/s connecting CPU and GPU
- Capable of performing dot product calculations at a rate of 9.6 billion per second
- Executes instructions in an in-order sequence
- Includes 768 bits of IBM eFUSE one-time programmable memory for security purposes
- Houses Microsoft’s Secure Bootloader and encryption hypervisor within ROM and a 64 KB SRAM block
- Utilizes a big-endian data format
XCGPU
With the introduction of the Xbox 360 S model, the XCGPU (codename Vejle) was launched, combining the Xenon CPU, Xenos GPU, and embedded DRAM onto a single silicon die. This integration aligns with industry trends aimed at lowering manufacturing costs by unifying CPU, GPU, memory controllers, and input/output components into one chip. Hardware compatibility is preserved by internally replicating the original front-side bus interface between CPU and GPU.
Produced by GlobalFoundries using a 45 nm fabrication process, the XCGPU integrates approximately 372 million transistors while achieving a 60% reduction in power usage and halving the chip’s physical size compared to its predecessor.
In 2014, the Winchester variant of the Xbox 360 adopted an even smaller XCGPU built on a 32 nm process (codename Oban), which further integrated eDRAM directly into the main die, removing the need for a multi-chip module configuration.
Gallery
Visual representations showcasing different processor iterations used in Xbox 360 and Xbox 360 S models.
References
- Xenon hardware overview authored by Pete Isensee, Development Lead at Xbox Advanced Technology Group.