The Xbox GPU consists of two main parts, which are the GPU core (500MHz) and the eDRAm Die.
The GPU communicates with the Xbox's CPU through its BIU (Bus Inteface Unit), which is directly connected to the CPU's FSB (Front Side Bus). The BIU is also connected to the main memory through the two GDDR3 memory controllers while the I/O unit connects it to the South Bridge. According to Microsoft, this configuration cuts down on latency when the CPU needs access to large chunks of main memory.
The GPU core also communicates with the main memory and the I/O circuit (South Bridge chip) through another unit, called the Memory Hub, which is directly connected to the memory controllers. The display controller is also fed with buffered frames through the Memory Hub unit. Notice that the Xbox uses an external (outside the GPU) DAC chip for video conversion.
Two GDDR3 memory controllers (2 x 64bit) are connected to the main 512MB memory. Each controller communicates with 256MB GDDR3 memory kits, at a maximum speed of 22.4GB/sec.
The eDRAM Die unit is manufactured by NEC (90nm process) and consists of an array of 192 processors, responsible for pixel processing such as anti-aliasing (AA) and alpha/Z processing etc. Microsoft has added a 10MB eDRAM memory unit for rendering inside the eDRAM Die directly connected to the rendering unit (256GB/sec), in order to avoid utilising resources from the main memory. The eDRAM Die unit is contained in the GPU unit.
The Xbox 360 is equipped with a huge 3-core CPU running at 3.2 GHz. A 1MB L2 cache is shared among all three CPU cores, and the communication with the GPU is achieved through a 21.6GB/sec FSB (Front Side Bus) channel.
South Bridge Connection through PCI express
The GPU is connected with the South Bridge chipset (I/O controlling unit) through a dual PCI Express interface (10GB/sec). The South Bridge chipset also includes an XMA decoder for audio, reducing the load on the CPU. The external I/O interfaces include SATA (20GB hard drive, 12x DL DVD recorder), USB Memory Unit ports (MU), ethernet controllers etc. The provided I/O interfaces look similar to those that will be found in Sony's Playstation 3.
GPU and CPU transistors
The GPU core unit uses 232,000,000 transistors while the eDRAm Die (Pixel processing unit) use 100,000,000 transistors.
The 232M transistors on GPU unit is about 40% more than those found on ATI's RADEON X800 (R420/423) GPU, and is almost equal to NVidia's GeForce 6800(NV40) system (222,000,000).
However, considering that Microsoft's early announcements for the Xbox concerning 48 Unified-Shaders, 232M transistors seems small. This might mean that ATI has possibly used some new techniques in the Unified-Shader design.
For comparison reasons, the GeForce 7800 GTX (G70) from NVIDIA uses 302,000,000 transistors for 32 Shaders. The RSX (Reality Synthesizer) GPU" installed in the Playstation 3, has a composition similar to the G70.
In addition, Microsoft disclosed the number of transistors of the Xbox 360 CPU. The CPU unit uses 165,000,000 transistors, a number equal to that found in a Pentium 4 6xx (Prescott 2M) CPU.
On the other hand, IBM's Cell processor on the Playstation 3 uses 241M transistors, which is roughly 1.5 more than those found on the Xbox.
Xbox hits the market soon
Xbox video game and entertainment system for as little as $299.99 U.S.
The Xbox 360 will make its debut in North America, Europe, and Japan in time for this holiday season, for $299.99 U.S (standard version). For gamers who want the ultimate experience right out of the box, Microsoft will offer a premium editionof the Xbox for the $399.99 U.S. The premium edition includes the Xbox 360 Console, a wireless controller, a removable faceplate, a HD AV Cable and many more.
For more information visit http://www.xbox.com/xbox360