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Rambus Dynamic Random Access Memory (RDRAM) is a memory subsystem designed to transfer data at faster rates. RDAM is made up of a random access memory (RAM), a RAM controller and a bus path that connect RAM to microprocessors and other PC devices.
RDRAM was introduced in 1999 by Rambus, Inc. RDRAM technology was considerably faster than older memory models, like the Synchronous DRAM (SDRAM). Typical SDRAM has a data transfer rate of up to 133 MHz, while the RDRAM can transfer data at a speed of upto 800 MHz.
RDRAM is also known as Direct RDRAM or Rambus.
RDRAM uses Rambus Inline Memory Module (RIMM) technology, which is installed in pairs, transfers data from rising and falling clock signal edges and doubles physical clock rates. RIMM data travels on a 16-bit bus that is similar to a packet network with transmitted data groups. Internal RIMM speeds operate from 400 MHz to 800 MHz via a 400-MHz system bus. A standard 400 MHz Rambus is known as PC-800 Rambus.
The RDRAM 16-bit bus uses a set of data processing features with a steady sequence stream, known as pipelining, that facilitate the output of one instruction prior to the input of the next instruction. Pipelining transfers RAM data to cache memory, allowing up to eight simultaneous data processing series. Pipelining also improves performance by increasing average successful message delivery rates when processing streams of data.
Design guidelines and a validation program by Intel and Rambus were intended to ensure RDRAM and RIMM module stability and to enhance earlier memory module requirements. Although RDRAM's increased bandwidth allowed faster data transfer, RAM cells experienced significant drops in performance, resulting in latency with additional RIMMs.
Latency improved in later RDRAM models, which were more expensive than Double Data Rate (DDR) SDRAM and Streaming Data Request (SDR) SDRAM. By 2004, Intel discontinued RDRAM in favor of DDR SDRAM and DDR-2 SDRAM modules.