Intel Roadmap Update June 1999 Part 3: Desktop Chipset and Mobile CPU Roadmap

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What Will Be The Benefit Of RDRAM?

Well, the CPU itself won't be able to benefit from Camino and the RDRAM much. If the Camino-platform should run at only 100 MHz front side bus, as e.g. with PIII 600/100 or PIII 650/100, the CPU won't be able to transfer more than 800 MB/s, regardless how fast the memory may be, because of the 64-bit (=8 Byte) wide memory bus running at 100 MHz FSB. Please remember that 800 MB/s could already be supplied by PC100 SDRAM. Running the FSB at 133 MHz, as e.g. with PIII 533/133, 600/133 or 667/133, gives a CPU peak data bus bandwidth of still 1.066 GB/s only. RDRAM at 400 MHz can supply a peak bandwidth of 1.6 GB/s, PC600 RDRAM can already supply up to 1.2 GB/s. Thus CPU depending applications won't benefit much from RDRAM at all and they'll only benefit if you run the FSB at 133 MHz.

The story looks a bit different when you consider that Intel was smart enough to equip Camino with AGP 4x as well. They pretty much had to, so the RDRAM was halfway worth our while. Applications that make heavy usage of the AGP, which are mainly 3D-games, could often enough run into arbitration problems when accessing main memory over the AGP whilst the CPU was trying to access main memory as well. AGP2x could transfer data at peaks of 533 MB/s, whilst the CPU at 100 MHz FSB could transfer data at up to 800 MB/s. PC100 only offered 800 MB/s bandwidth though, and so arbitration problems were more than likely. AGP 4x is now able to transfer data at up to 1.066 GB/s, just as a CPU at 133 MHz FSB, so that the 1.6 GB/s supplied by PC800 RDRAM are indeed useful in case an application takes advantage of AGP4x. We'll have to see how much of a difference AGP4x is going to make with the games though. After all we shouldn't forget that one of the currently fastest graphics chips, the Voodoo3 from 3Dfx, is not even taking real advantage of AGP2x right now (no AGP-texturing support) and it's still performing very respectable. Compared to the bandwidth of memory mounted on the graphics-card, which ranges from 2.3 GB/s (3Dfx Voodoo3 2000) to over 4.5 GB/s (Matrox G400), the AGP4x bandwidth is still pretty pathetic.