Andir said:
You do know that the average PC Bus is less than 15-18GB/s and runs at 32bit? Only with technologies like HyperTransport and the like are you getting up to 20GB/s. |
Actually, the average PC memory bus (that is what we're talking about, isn't it?) is 64-bit. And ever since the nForce chipset, which has been around for the last 6 years, PC motherboards have supported dual-channel memory configurations, which effectively gives them... wait for it... a 128-bit memory bus.
The difference, of course, is the clock speed of the memory. The PS3 uses Rambus XDR RAM running at 3.2 GHz, whereas PCs are only up to 667 MHz (with DDR, effectively 1333 MHz). BTW, the PS3's memory bus isn't 128-bit, either. It actually uses four channels that are 8 bits wide each, and transfers twice per clock cycle just like DDR, for an effective 6.4 GHz, 32-bit data path. That results in 25.6 GB/s of bandwidth. By comparison, a dual-channel DDR3 1333 setup would result in 21.3 GB/s of bandwidth. A typical PC from around the time the PS3 launched would have used DDR2 800 for 12.8 GB/s, hence why the PS3 was advertised as having twice the memory bandwidth as a high-end PC.
The Rambus XDR memory is a lot like the old RDRAM that the first Pentium 4s used. It runs at very high frequency comared to SDRAM, but on a narrow bus.
