RDRAMs - Rambus Memory
Say goodbye to the old familiar SDRAM modules. The i820 chipset only supports RDRAM memory. This new memory technology provides twice the bandwidth of conventional SDRAMs. The only two drawbacks are the memory cost and slower latency. The RDRAM cost is nearly 5 times the cost of SDRAM PC-100 memory, but as SDRAM-prices rise, the difference may shrink. It still adds a whole lot of additional cost to an i820 based system though. Also, you will find that i820 based systems will always have every memory bank filled. If the memory slot doesn't have a RDRAM RIMM module installed it must have a continuity module called a CRIMM in the memory socket. The CRIMM(s) is required to avoid any reflections with the high speed Rambus-interface.
Here is a photo showing a RDRAM RIMM module (blue) with two CRIMM or continuity modules.
Future i82x chipsets will provide support for PC-133 SDRAM but all of the memory accesses will be forced to go through the MTH, otherwise called 'Memory Translator HUB'. I don't have all the details regarding this new HUB but I'm expecting some performance hits due to the translation process. The i820 chipset supports various RDRAM speeds. However, not all of these options are available to every FSB frequency. Here is a table that depicts supported frequencies.
|Memory Bus Speed||300MHz||356MHz||400MHz|
|Processor Host Bus
|Processor Host Bus
RIMM Sizes 64MB, 96MB, 128MB, 256MB
Is there a new CPU that supports 133MHz Bus?
There is a different processor that supports the i820's 133MHz FSB. Basically, it the same old Pentium III processor that has been qualified to run with the new higher bus speed. The main difference between the current Pentium III and the new one is the bus multiplier each CPU is clocked at. Today's Pentium III 600 runs with a FSB frequency of 100MHz and a multiplier of 6x. A Pentium III that supports the higher 133MHz FSB has a lower multiplier for a 600MHz core. With a 133MHz FSB the multiplier would be 4.5x. The new 133MHz capable Pentium III's will be labeled 533B (for 533MHz) and 600B (for 600MHz). Other than the 'B' at the end of the CPU's frequency, nothing has changed about the new, or is it old, Pentium III processors. Even though most of the current shipping processors could probably handle the higher 133MHz FSB, the problem would be the higher locked multiplier. It would be out of the question to expect a 600/100MHz part with a locked multiplier of 6x to run with a 133MHz FSB at 798MHz, but it may be a nice chance to overclock e.g. a Pentium III 450 to 600 MHz.