What's With All Of The Memory
When I first saw the i845 chipset based motherboards last year, I was appalled. Who would have thought that Intel would want to pair up the Pentium 4 processor with SDRAM?
As it was, I am a bit uneasy at the idea of an Athlon running on anything but DDR these days, but it wasn't so disturbing because the original Athlon processors ran on SDRAM platforms. There was never anything but an SDRAM based Slot A Athlon system.
Pentium 4s typically use RAMBUS Inline Memory Modules, or RIMMs for short.
RIMMs use a high-speed narrow, 16-bit wide serial bus for transfers. PC800 RIMMs operate at 400MHz DDR, which calculates to an effective 800MHz. This allows for a theoretical peak transfer rate of 1600 MB/s (800 MHz x 2 bytes).
The system bus of a Pentium 4 is 100 MHz, and your typical PC100 SDRAM has a peak transfer rate of only 800 MB/s (100 MHz x 8 bytes). Knowing this, I had thought that the i845 SDRAM boards wouldn't last. I honestly believed that no one in his or her right mind would buy one.
As it turns out, people actually opted for a crippled Pentium 4 running with SDRAM instead of an AMD Athlon as way to build an affordable computer.
As I write this, a stick of 512MB SDRAM sells for $135; the highest it's been in a long time. But two 256 MB RIMMs (got to get two because today's RIMM based chipsets install RIMMs in pairs) go for $185 (same vendor). That's $50 that could be used for something else...like a faster processor, maybe?
PC1600 DDR, like PC800 RAMBUS, has a theoretical peak transfer rate of 1600 MB/s (200MHz X 8 bytes), hence the name. Despite the similar peak transfer rates, RIMMs still look faster on paper than DDR. The reason why RAMBUS wins out on the memory benchmarks goes back to the ancient PC analogy of cars moving down an 8-lane highway versus a 2-lane highway. Bandwidth, bandwidth, bandwidth.
>> Pentium 4 Meets DDR/About The Benchmarks