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rdram, rdram pc1066
Rambus DRAM RDRAM, and its successors Concurrent Rambus DRAM CRDRAM and Direct Rambus DRAM DRDRAM, are types of synchronous dynamic RAM developed by Rambus from the late-1980s 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 However, RDRAM got embroiled in a standards war with an alternative technology—DDR SDRAM—and quickly lost out on grounds of price, and later, performance By around 2003, DRDRAM was no longer supported by any personal computer


  • 1 PC main memory
    • 11 Module specifications
      • 111 Continuity modules
    • 12 Performance
    • 13 Benchmarks
    • 14 Marketing history
  • 2 Other uses
    • 21 Video game consoles
    • 22 Texas Instruments DLP
    • 23 Video cards
  • 3 See also
  • 4 References
  • 5 External links

PC main memoryedit

The first PC motherboards with support for RDRAM debuted in late 1999, after two major delays RDRAM was controversial during its widespread use by Intel for having high licensing fees, high cost, being a proprietary standard, and low performance advantages for the increased cost RDRAM and DDR SDRAM were involved in a standards war 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, ie 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

RDRAM memory with integrated heat spreader A Samsung RDRAM 6400 128 MB A Samsung RDRAM Installed with Pentium 4 15 GHz

Moreover, if a mainboard has a dual- or quad-channel memory subsystem, all of the memory channels must be upgraded simultaneously 16-bit modules provide one channel of memory, while 32-bit modules provide two channels Therefore, a dual channel mainboard accepting 16-bit modules must have RIMMs added or removed in pairs A dual channel mainboard accepting 32-bit modules can have single RIMMs added or removed as well Note that some of the later 32 bit modules had 232 pins as compared to the older 184 pin 16 bit modules1

Module specificationsedit

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

Continuity modulesedit

A Rambus continuity RIMM CRIMM, also known as terminator or dummy

The design of many common Rambus memory controllers dictated that memory modules be installed in sets of two Any remaining open memory slots must be filled with continuity RIMMs CRIMMs These sticks provide no extra memory, and only served to propagate the signal to termination resistors on the motherboard instead of providing a dead end where signals would reflect CRIMMs appear physically similar to regular RIMMs, except they lack integrated circuits and their heat-spreaders


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 adding about a 5 percent penalty at 64 Mbit1 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 heatspreaders on all RIMM devices RDRAM includes additional circuitry such as packet demultiplexers 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 feescitation needed 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

With the introduction of the Intel 840 Pentium III, Intel 850 Pentium 4, Intel 860 Pentium 4 Xeon chipsets, Intel added support for dual-channel PC-800 RDRAM, doubling bandwidth to 3200 MB/s by increasing the bus width to 32-bit This was followed in 2002 by the Intel 850E chipset, which introduced PC-1066 RDRAM, increasing total dual-channel bandwidth to 4200 MB/s In 2002, Intel released the E7205 Granite Bay chipset, which introduced dual-channel DDR support—for a total bandwidth of 4200 MB/s - at a slightly lower latency than competing RDRAM The bandwidth of Granite Bay matched that of the i850E chipset using PC-1066 DRDRAM with considerably lower latency

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


Benchmark tests conducted in 1998 and 1999 showed most everyday applications to run minimally slower with RDRAM In 1999, benchmarks comparing the Intel 840 and Intel 820 RDRAM chipsets with the Intel 440BX SDRAM chipset led to the conclusion that the performance gain of RDRAM did not justify its cost over SDRAM except for use in workstations In 2001, benchmarks pointed out that single-channel DDR266 SDRAM modules could closely match dual-channel 800 MHz RDRAM in everyday applications2

Marketing historyedit

In November 1996, Rambus entered into a development and license contract with Intel3 Intel announced that it would only support the Rambus memory interface for its microprocessors,4 and had been granted rights to purchase one million shares of Rambus' stock at $10 per share5

As a transition strategy, Intel planned to support PC-100 SDRAM DIMMs on future Intel 82x chipsets using Memory Translation Hub MTH6 In 2000, Intel recalled the Intel 820 motherboard which featured the MTH due to occasional occurrences of hanging and spontaneous reboots caused by simultaneous switching noise7 Since then, no production Intel 820 motherboards contain MTH

In 2000, Intel began to subsidize DRDRAM by bundling retail boxes of Pentium 4s with two RIMMs8 Intel began to phase out these subsidies in 20019

In 2003, Intel introduced the 865 and 875 chipsets with dual-channel DDR SDRAM support, which were marketed as high-end replacements of the 850 chipset Furthermore, the future memory roadmap did not include DRDRAM10

Other usesedit

Video game consolesedit

RDRAM18-NUS on Nintendo 64

Rambus's RDRAM saw use in three video game consoles, beginning in 1996 with the Nintendo 64 The Nintendo console utilized 4 MB RDRAM running with a 500 MHz clock on a 9-bit bus, providing 500 MB/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 allowed circuit board designers to use simpler design techniques to minimize cost The memory, however, was disliked for its high random access latencies In the N64, the RDRAM modules are cooled by a passive heatspreader assembly2 Nintendo also included a provision for upgrading the system's memory with the Expansion Pak accessory, allowing certain games to be enhanced with either enhanced graphics, higher resolution or increased framerate A Jumper Pak dummy unit is included with the console due to the aforementioned design quirks of RDRAM

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 DLPedit

RDRAM was used in Texas Instruments DLP systems11

Video cardsedit

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 potentially faster user experience than competing DRAM technologies with its high bandwidth The chips were used on the Creative Graphics Blaster MA3xx series, among others

See alsoedit

  • List of device bandwidths
  • SLDRAM, an alternative open standard


  1. ^ rdramrambusmemorycom
  2. ^ Gavrichenkov, Ilya "ASUS P4B266 Mainboard Review" Xbit Laboratories Retrieved 17 May 2013 
  3. ^ EDACafe Weekly : Memory Continued - October 04, 2004
  4. ^ What is RDRAM - A Word Definition From the Webopedia Computer Dictionary
  5. ^ NewsWire Issue 97-8
  6. ^ Intel i820 Chipset Review | Tom's Hardware
  7. ^ cw062100 - Intel i820 MTH recall Archived July 24, 2009, at the Wayback Machine
  8. ^ Intel chips in for cheaper Pentium 4 PCs | Tech News on ZDNet
  9. ^ Intel drops Rambus subsidies - CNET Newscom
  10. ^ RAM Wars: Return of the JEDEC | Tom's Hardware
  11. ^ Press Release - Rambus Technology XDR

External linksedit

  • RDRAM on the Rambus website
  • Reference where information about dual-channel RDRAM in the PS2 can be found
  • How to install RAMBUS memory
  • Illustrated Guide for Installing RDRAM

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