Rambus RDRAM memory

Rambus RDRAM memory

Direct Rambus DRAM or DRDRAM (sometimes just called Rambus DRAM or RDRAM) is a type of synchronous dynamic RAM, designed by the Rambus Corporation.

Rambus Dynamic RAM memory technology, was intended to replace SDRAM and challenge DDR SDRAM as the standard memory used in computers. The first PC motherboards with support for RDRAM debuted in 1999. They supported PC800 RDRAM, which operated at 400 MHz but presented data on both rise and fall of clock cycle resulting in effectively 800 MHz, and delivered 1600 MB/s of bandwidth over a 16-bit bus using a 184-pin RIMM form factor. This was significantly faster than the previous standard, PC133 SDRAM, which operated at 133 MHz and delivered 1066 MB/s of bandwidth over a 64-bit bus using a 168-pin DIMM form factor.

Some downsides of RDRAM technology, however, included significantly increased latency, heat output, manufacturing complexity, and cost. PC800 RDRAM operated with a latency of 45 ns, compared to only 7.5 ns for PC133 SDRAM. RDRAM memory chips also put out significantly more heat than SDRAM chips, necessitating heatsinks on all RIMM devices. RDRAM also includes a memory controller on each memory chip, significantly increasing manufacturing complexity compared to SDRAM, which used a single memory controller located on the northbridge chipset. RDRAM was also two to three times the price of PC133 SDRAM due to manufacturing costs, license fees and other market factors. DDR SDRAM, introduced in 2000, operated at an effective clockspeed of 266 MHz and delivered 2100 MB/s over a 64-bit bus using a 184-pin DIMM form factor.

With the introduction of the i840 chipset, Intel added support for dual-channel PC800 RDRAM, doubling bandwidth to 3200 MB/s by increasing the bus width to 32-bit. This was followed in 2002 by the i850E chipset, which introduced PC1066 RDRAM, increasing total dual-channel bandwidth to 4200 MB/s. Also in 2002, Intel released the E7205 Granite Bay chipset, which introduced dual-channel DDR support for a total bandwidth of 4200 MB/s, but at a much lower latency than competing RDRAM. In 2003, Intel released the i875P chipset, and along with it dual-channel DDR400. With a total bandwidth of 6400 MB/s, it marked the end of RDRAM as a technology with competitive performance.

Rambus survived the obsolescence of RDRAM and moved to support DDR and DDR2 in the area of video card technology and in particular, PCI-E. Rambus also developed and licensed its XDR RAM technology.



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