RDRAM
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- 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.
Features
Image:Rdram.png The Direct RDRAM features an architecture and a protocol designed to achieve high bandwidth. The Rambus channel architecture has a single-device upgrade granularity, offering engineers the ability to balance performance requirements against system capacity and component count. The narrow, high-performance channel also offers performance and capacity scalability through the use of multiple channels in parallel. In addition, the validation program created by Intel and Rambus promotes system stability by ensuring that devices and modules conform to published specifications. Although RDRAMs have a low pin count, a single device is capable of providing up to 1.6 GB/s bandwidth. Memory systems that use RIMMs (Rambus Inline Memory Modules), also known as RDRAM modules, employ a narrow, uniform-impedance transmission line, the Rambus Channel, to connect the memory controller to a set of RIMMs. Low pin count and uniform interconnection topology allow easy routing and reduction of pin count on the memory controller. While a single channel is capable of supplying 1.6 GB/s of bandwidth, multiple channels can be used in parallel to increase this number. Systems that use, for example, the Intel 840 chipset, have two parallel Rambus channels, and are able to handle up to 3.2 GB/s.
Providing high bandwidth from a single device also allows memory systems to be constructed from small numbers of RDRAMs. The Sony PlayStation 2 uses two RDRAM channels, each with a single RDRAM stick, to achieve a total of 3.2 GB/s memory bandwidth.
While RDRAM technology was designed to be cheaper to implement on the system level, the RIMM sticks themselves were not easy to manufacture in the beginning. Similar to how the Pentium Pro CPU could not be tested until both dies were integrated into the final package, the RIMM sticks needed to be completely assembled before testing could be performed. This created the scenario where if just one of the RDRAM chips was faulty, the entire stick had to be thrown away.
Early implementations suffered from much higher memory latency when compared to contemporary SDR SDRAM and DDR SDRAM designs, making SDR SDRAM or DDR SDRAM a better choice. Latency became worse as additional RIMM's were added to the system, further hurting performance. Nintendo 64's implementation was regarded as a very high latency memory subsystem.
Later designs mitigated the latency issue to the point where it was mostly competitive with DDR SDRAM, but by then Rambus had largely alienated hardware manufacturers due to its litigious nature. Consumer sentiment turned against Rambus in the same manner, and also because of RDRAM's substantially higher price compared to other memory types. As of 2004, Intel had essentially abandoned RDRAM entirely, with all new products using DDR SDRAM or DDR2 SDRAM.
RDRAM memory sticks are available in a number of different speeds. Quite fittingly, PC800 has an 800MHz data rate using a 400MHz clock rate, PC1066 has a 1066MHz data rate using a 533MHz clock rate, etc. This is best described in Intel’s Developer UPDATE Magazine June 2002 article "Mainstream PC Memory Architectures for the Intel Pentium 4 Processor". This use of Double Data Rate technology was included in RAMBUS’ patent portfolio, after being discussed openly in JEDEC meetings. RAMBUS used the patent to file several lawsuits against DDR SDRAM manufacturers. While a few companies settled, others challenged the lawsuit, and ownership of said intellectual property was eventually denied.
Uses
Rambus DRAM has been used in the Nintendo 64, the Sony PlayStation 2,alpha 21364 servers, and a line of Cray supercomputers. Intel originally advocated the use of RDRAM in desktop PCs. Due to fears that Intel was trying to control the memory market through Rambus Corp., most of the main memory manufacturers sought to replace RDRAM with an alternative standard, DDR (Double Data Rate) DRAM. Better manufacturability led to DDR prevailing over RDRAM in the cost-conscious PC market. Rambus's successor to RDRAM is XDR DRAM, used by IBM’s "Cell" processor technology and the PlayStation 3.
External links
es:RIMM fr:RDRAM he:RDRAM nl:Rambus Inline Memory Module pt:Rambus