Rambus DRAM (RDRAM) : Specifications, Performance, and Uses

 

Rambus DRAM (RD-RAM):

 

Rambus DRAM (RDRAM), and its successors Concurrent Rambus DRAM (CRDRAM) and Direct Rambus DRAM (DRDRAM), are types of synchronous dynamic random-access memory (SDRAM) developed by Rambus from the 1990s through to the early-2000s. The third-generation of Rambus DRAM, DRDRAM was replaced by XDR DRAM. Rambus DRAM was developed for high-bandwidth applications, and was positioned by Rambus as replacement for various types of contemporary memories, such as SDRAM.

DRDRAM was initially expected to become the standard in PC memory, especially after Intel agreed to license the Rambus technology for use with its future chipsets. Further, DRDRAM was expected to become a standard for graphics memory. By around 2003, DRDRAM was no longer supported by any personal computer.

PC-800 RDRAM operated at 400 MHz and delivered 1600 MB/s of bandwidth over a 16-bit bus. It was packaged as a 184-pin RIMM (Rambus In-line Memory Module) form factor, similar to a DIMM (Dual In-line Memory Module). Data is transferred on both the rising and falling edges of the clock signal, a technique known as DDR. To emphasize the advantages of the DDR technique, this type of RAM was marketed at speeds twice the actual clock rate, i.e. the 400 MHz Rambus standard was named PC-800. This was significantly faster than the previous standard, PC-133 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.

Fig: Samsung RDRAM 6400 128 MB

Module specifications:

Designation	Bus width (bits)	Channels	Clock rate (MHz)	Bandwidth (MB/s)
PC600	16	Single	266	1066
PC700	16	Single	355	1420
PC800	16	Single	400	1600
PC1066 (RIMM 2100)	16	Single	533	2133
PC1200 (RIMM 2400)	16	Single	600	2400
RIMM 3200	32	Dual	400	3200
RIMM 4200	32	Dual	533	4200
RIMM 4800	32	Dual	600	4800
RIMM 6400	32	Dual	800	6400

 

Performance:

Compared to other contemporary standards, Rambus showed increase in latency, heat output, manufacturing complexity, and cost. Because of more complex interface circuitry and increased number of memory banks, RDRAM die size was larger than that of contemporary SDRAM chips, and results in a 10–20 percent price premium at 16 Mbit densities. Note that the most common RDRAM densities are 128 Mbit and 256 Mbit.

PC-800 RDRAM operated with a latency of 45 ns, more than that of other SDRAM varieties of the time. RDRAM memory chips also put out significantly more heat than SDRAM chips, necessitating heat spreaders on all RIMM devices. RDRAM includes additional circuitry (such as packet de-multiplexers) on each chip, increasing manufacturing complexity compared to SDRAM. RDRAM was also up to four times the price of PC-133 SDRAM due to a combination of higher manufacturing costs and high license fees. PC-2100 DDR SDRAM, introduced in 2000, operated with a clock rate of 133 MHz and delivered 2100 MB/s over a 64-bit bus using a 184-pin DIMM form factor.

To achieve RDRAM's 800 MHz clock rate, the memory module runs on a 16-bit bus instead of a 64-bit bus in contemporary SDRAM DIMM. At the time of the Intel 820 launch some RDRAM modules operated at rates less than 800 MHz.

Uses:

Video game consoles:

Rambus's RDRAM saw use in two video game consoles, beginning in 1996 with the Nintendo 64. The Sony PlayStation 2 was equipped with 32 MB of RDRAM, and implemented a dual-channel configuration resulting in 3200 MB/s available bandwidth.

Texas Instruments DLP:

RDRAM was used in Texas Instruments' Digital Light Processing (DLP) systems.

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.