HANDS ON GUIDE

Graphics

Discussing the power of the PS3 compared with that of the 360 is a favourite sport of console fanboys and the mainstream media, but the differences between the gamepad architecture of both machines and a PC makes a head-to-head comparison in terms of numbers pretty meaningless. Far more important are the end results - and in this respect, it's easy to compare the consoles and the PC because of the number of games available across all three platforms.

First, however, a quick rundown of the processing power that the 360 and PS3 have available. It will come as no surprise to CPC readers that the consoles split along party lines - ATI makes GPUs for the 360 and Wii, and Nvidia provides the GPU for the PS3. The 360's GPU features a unified shader architecture but, with only 48 stream processors, and clocked at 500MHz, its Xenos GPU doesn't seem to compare particularly well with even mid-range graphics GPUs such as the GeForce 8800 GT (112 stream processors clocked at 1.5GHz, with the rest of the GPU running at 600MHz). It still has some interesting cards to play, particularly the fact the GPU is paired with a 10MB embedded RAM module on the same die. Data can be transferred between GPU and the eDRAM at 32GB/sec, around half the speed at which the GeForce 8800 GT can access its memory. The eDRAM die also contains logic for functions such as Z-buffering, alpha blending and AA, to the point where using 4x AA doesn't result in much of a performance penalty.

In addition to the eDRAM module, the 360 has 512MB of GDDR3 system memory, clocked at 700MHz (1.4GHz effective), which both the GPU and CPU can access. There's around 22.4GB/sec of memory bandwidth for both chips, compared to 12.8GB/sec for the PC's CPU and 57.6GB/sec for the 8800 GT. The 360's CPU is a 64-bit PowerPC chip, built by IBM, but it was designed specifically for the 360. It has three cores, each of which can handle two threads at a time. Each core is clocked at 3.2GHz, and has 2 x 32KB of Level 1 cache, along with 1MB of Level 2 cache shared by all three. As with AMD's Phenom quad-core CPUs, the three cores communicate via a crossbar switch.

The PS3's GPU, the Reality Synthesizer (RSX), is at heart a GeForce 7-series GPU, with discreet pixel and vertex shaders (remember those?). Its specs are very similar to those of the 7800 GTX: 24 pixel processors, eight vertex shaders and six ROPs, all clocked at 550MHz. As with PC graphics cards, the RSX has its own separate framebuffer - 256MB of 700MHz (1.4GHz effective) GDDR3, giving 22.4GB/sec of bandwidth.

The PS3 has 256MB of XDR system memory for its Cell CPU. Like the 360's CPU, the Cell has multiple cores, is in part PowerPC-based, and is clocked at 3.2GHz. However, its eight cores, aren't identical. The heart of the chip is the Power Processor Element (PPE), which can process two threads at once, similar to an Intel CPU with Hyper-Threading. There are then seven smaller, simpler Synergistic Processing Elements (SPEs), 128-bit RISC processors with 256KB of embedded memory each. The Cell design has massive floating-point performance thanks to the SPEs, but they're less suited for bigger, more general computational tasks.

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