Rambus Dynamic Random Access Memory
RDRAM is a memory technology created by the company Rambus. There are three RDRAM technologies: Base RDRAM, Concurrent RDRAM and Direct RDRAM. The first two are video memory technologies, while the third can be used as PC RAM memory.
Rambus technology works by transmitting just a few bits at a time (e.g. 16 bits) but with a very high clock rate.
Direct RDRAM memories are sold in memory modules called RIMM that are classified like as follows:
- 1st generation (16 bits): PC600 or RIMM 1200 (1,200 MB/s), PC700 or RIMM 1400 (1,400 MB/s) and PC800 or RIMM 1600 (1,600 MB/s).
- 2nd generation (32 bits): PC1066 or RIMM 4200 (4,200 MB/s).
- 3rd generation (64 bits): PC1333 or RIMM 11G (10.7 GB/s).
You can only install RIMM modules on motherboards that accept this kind of memory, and they are very rare nowadays.
Usually dual channel configuration is used, doubling the nominal transfer rate if two memory modules are used. For example, on a motherboard based on Intel 850 chipset with two PC800 modules installed, the maximum memory transfer rate will be of 3,200 MB/s (1,600 MB/s x 2), since this chipset uses dual channel configuration.
This technology requires a resistive termination. Because of that all RIMM sockets located on the motherboard must have a module installed. In the case you don’t have enough memory modules to fill all sockets, you must install an empty module called C-RIMM (Continuity RIMM).
RDRAM memories for PCs are gone, mainly because to use this technology manufacturers had to pay royalties to Rambus. With the introduction of DDR-SDRAM memories the use of RDRAM memories didn’t make sense anymore.