Rambus DRAM or RDRAM is a type of synchronous dynamic RAM, created by the Rambus Corporation. It has also been incorporated into the Sony PlayStation 2 and a line of Cray Supercomputers. Intel originally advocated the use of RDRAM in all Pentium 4 motherboards. Due to fears that Intel was trying to control the memory market through Rambus Corp., most of the main memory manufacturers actively sought ways to replaced RDRAM with a next generation standard. They accomplished this by introducing DDR (Double Data Rate) DRAM. When introduced, there was extensive ongoing litigation as to the extent to which this memory incorporated RDRAM technologies. With limited production of RDRAM by these manufacturers and an insurgence of DDR on the market Intel was forced to abandon their exclusive support of RDRAM and introduce DDR support for the Pentium 4 motherboard. A new technology, however, may soon replace DRAM: Rambus' XDR-DRAM, which is being incorporated into the Sony PlayStation 3 and supported with IBM’s "Cell" processor technology.
The Direct RDRAM, or RDRAM, features an architecture
and a protocol that were 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 module} or (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, to achieve a total of 3.2 GB/s memory bandwidth.
In order to ensure stability of RDRAM memory systems, design guidelines and a
validation program have been put in place that surpass requirements set for
previous memory technologies. Intel and Rambus have defined system specs to
ensure robustness of RDRAMs and of the channel to the memory controller.
In addition, they have created a rigorous validation programs for certification of RDRAMs and RIMM modules.
Computer memory
