RDRAM

RIMM redirects here. For the psychologist, see Sylvia Rimm.

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

Architecture

Implementations

Personal Computers

The first PC motherboards with support for RDRAM debuted in 1999. They supported PC-800 RDRAM, which operated at 400 MHz and delivered 1.6 GiB/s of bandwidth over a 16-bit bus using a 184-pin RIMM form factor. Data is tranferred on both the raising and the falling edges of the clock signal (double data rate). This was significantly faster than the previous standard, PC-133 SDRAM, which operated at 133 MHz and delivered 1.066 GiB/s of bandwidth over a 64-bit bus using a 168-pin DIMM form factor.

Compared to other current standards, Rambus shows significantly increased latency, heat output, manufacturing complexity, and cost. PC-800 RDRAM operated with a latency of 45 ns, compared to only 7.5 ns for PC-133 SDRAM. RDRAM memory chips also put out significantly more heat than SDRAM chips, necessitating heatspreaders on all RIMM devices. RDRAM 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 PC-133 SDRAM due to a combination of high manufacturing costs and high license fees. PC-2100 DDR SDRAM, introduced in 2000, operated with a clockspeed of 133 MHz and delivered 2.1 GiB/s over a 64-bit bus using a 184-pin DIMM form factor.

Also, if one were only using a single stick of RDRAM (or 3 sticks if the motherboard supports 4 RDRAM sticks) you had to use C-RIMM to cancel out the other RAM slot. These sticks provided no extra memory, and only served to terminate the other slot. The picture on the Lower right depicts a C-RIMM stick.

With the introduction of the i840 chipset, Intel added support for dual-channel PC-800 RDRAM, doubling bandwidth to 3.2 GiB/s by increasing the bus width to 32-bit. This was followed in 2002 by the i850E chipset, which introduced PC-1066 RDRAM, increasing total dual-channel bandwidth to 4.2 GiB/s. Then in 2002, Intel released the E7205 Granitebay chipset, which introduced dual-channel DDR support for a total bandwidth of 4.2 GiB/s, but at a much lower latency than competing RDRAM. In 2003, Intel released the i875P chipset, and along with it dual-channel PC-3200 with total bandwidth of 6.4 GiB/s.

Stick/module specification

PC-600: RDRAM-RIMM specified to operate at 300 MHz, 1.200 GiB/s bandwidth (16-bit, single-channel RIMM)
PC-700: RDRAM-RIMM specified to operate at 355 MHz, 1.420 GiB/s bandwidth (16-bit, single-channel RIMM)
PC-800: RDRAM-RIMM specified to operate at 400 MHz, 1.600 GiB/s bandwidth (16-bit, single-channel RIMM)
PC-1066: RDRAM-RIMM specified to operate at 533 MHz, 2.133 GiB/s bandwidth (16-bit, single-channel RIMM)
PC-1200: RDRAM-RIMM specified to operate at 600 MHz, 2.400 GiB/s bandwidth (16-bit, single-channel RIMM)

Video Game Consoles

Rambus's RDRAM saw use in several video game consoles, beginning in 1996 with the Nintendo 64. The Nintendo console utilized 4 MiB RDRAM running with a 500 MHz clock on an 8-bit bus, providing 500 MiB/s bandwidth. RDRAM allowed N64 to be equipped with a large amount of memory bandwidth while maintaining a lower cost due to design simplicity. RDRAM's narrow bus allows circuit board designers to use simpler design techniques to minimize cost. The memory, however, was disliked for its high RAM access latencies. In the N64, the RDRAM modules are cooled by a passive heatspreader assembly.^*

Sony used RDRAM in both PlayStation 2 and PlayStation 3. The PS2 was equipped with 32 MiB of the memory, and implemented it in a way as to have 3.2 GiB/s bandwidth available. PS3 utilizes 256 MiB of Rambus's XDR DRAM on a 64-bit bus at 3.2 GHz, allowing a large 25.6 GiB/s bandwidth, again on a relatively narrow data path.

Video Cards

Cirrus Logic implemented RDRAM support in their Laguna graphics chip, with two members of the family; the 2D-only 5462 and the 5464, a 2D chip with 3D acceleration. RDRAM offered a cost-advantage while being potentially faster than competing DRAM technologies with its high bandwidth. The chips were used on the Creative Graphics Blaster MA3xx series, among others.

External links

RDRAM on the Rambus website

Computer memory