RDRAM
Encyclopedia
Direct Rambus DRAM or DRDRAM (sometimes just called Rambus DRAM or RDRAM) is a type of synchronous dynamic RAM
. RDRAM was developed by Rambus
inc., in the mid-1990s as a replacement for then-prevalent DIMM
SDRAM
memory architecture.
RDRAM 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, RDRAM was expected to become a standard for VRAM
. However, RDRAM got embroiled in a standards war with an alternative technology - DDR
SDRAM
, quickly losing out on grounds of price, and, later on, performance. By the early 2000s, RDRAM was no longer supported by any mainstream computing architecture.
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, which 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
. For marketing reasons the physical clock rate was multiplied by two (because of the DDR operation); therefore, 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.
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 modules.
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 circuit
s.
PC-800 RDRAM operated with a latency of 45 ns
, which was more latency than other comparable DRAM technologies of the time. RDRAM memory chips also put out significantly more heat than SDRAM chips, necessitating heatspreaders on all RIMM devices. RDRAM includes a memory controller on each memory chip, significantly increasing manufacturing complexity compared to SDRAM, which used a single memory controller located on the northbridge
chipset. RDRAM was also two to three times the price of PC-133 SDRAM due to a combination of high 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.
When installing multiple RIMMs on a memory channel, performance impact is greater than SDRAM design because the data in the further memory module has to travel across all memory chips installed physically closer to the memory controller, instead of just 1 or 2 chips in production SDRAM motherboards.
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. Then 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. Granite Bay matched i850E + PC-1066 RDRAM bandwidth with considerably lower latency.
To achieve RDRAM's 800 MHz clock rate, the memory module only runs on 16-bit bus, instead of 64-bit bus in contemporary SDRAM DIMM. Furthermore, not all production RDRAM modules at the time of the Intel 820 launch could run at 800 MHz; instead, they ran at a slower clock rate.
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 2002, benchmarks pointed out that single-channel DDR400 SDRAM modules could closely match dual-channel 1066 MHz RDRAM in everyday applications.
development community
that it would only support the Rambus memory interface for its microprocessor
s, Intel was granted rights to purchase 1M shares of Rambus' stock at $10 per share.
As a transition strategy, Intel planned to support PC-100 SDRAM DIMM on future Intel 82x chipsets using Memory Translation Hub (MTH). In 2000, Intel recalled the Intel 820 motherboard with memory translator hub (MTH) because the MTH can, while doing simultaneous switching, produce noise
that may cause the computer to hang mysteriously or to spontaneously reboot. Since then, no production Intel 820 motherboards contain MTH.
In 2000, Intel subsidized RDRAM by bundling retail boxes of Pentium 4 CPUs with 2 RIMMs. Intel began to phase out Rambus subsidies in 2001.
In 2003, Intel introduced Intel 865 and Intel 875 chipsets, which were marketed as high end replacements of Intel 850. Furthermore, the future memory roadmap did not include Rambus.
. 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 allows 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 assembly.http://n64.icequake.net/
Sony uses RDRAM in the PlayStation 2
. The PS2 was equipped with 32 MB of the memory, and implemented a dual-channel configuration resulting in 3200 MB/s available bandwidth. The PlayStation 3
utilizes 256 MB of Rambus's XDR DRAM
, which could be considered a successor to RDRAM, on a 64-bit bus at 400 MHz with an octal data rate (cf. double data rate
) providing a clock rate of 3.2 GHz, allowing a large 204.8 Gbit/s (25.6 GB/s) bandwidth.
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 than competing DRAM technologies with its high bandwidth. The chips were used on the Creative
Graphics Blaster MA3xx series, among others.
Dram
Dram or DRAM may refer to:As a unit of measure:* Dram , an imperial unit of mass and volume* Armenian dram, a monetary unit* Dirham, a unit of currency in several Arab nationsOther uses:...
. RDRAM was developed by Rambus
Rambus
Rambus Incorporated , founded in 1990, is a technology licensing company. The company became well known for its intellectual property based litigation following the introduction of DDR-SDRAM memory.- History :...
inc., in the mid-1990s as a replacement for then-prevalent DIMM
DIMM
A DIMM or dual in-line memory module, comprises a series of dynamic random-access memory integrated circuits. These modules are mounted on a printed circuit board and designed for use in personal computers, workstations and servers...
SDRAM
SDRAM
Synchronous dynamic random access memory is dynamic random access memory that is synchronized with the system bus. Classic DRAM has an asynchronous interface, which means that it responds as quickly as possible to changes in control inputs...
memory architecture.
RDRAM 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, RDRAM was expected to become a standard for VRAM
VRAM
Video RAM, or VRAM, is a dual-ported variant of dynamic RAM , which was once commonly used to store the framebuffer in some graphics adapters....
. However, RDRAM got embroiled in a standards war with an alternative technology - DDR
DDR
DDR may refer to:In entertainment:*Dance Dance Revolution, a music video game series by Konami*DDR , a Norwegian rock band singing in German.*DDR , a Greenlandic punk band singing in Danish.In organizations:...
SDRAM
SDRAM
Synchronous dynamic random access memory is dynamic random access memory that is synchronized with the system bus. Classic DRAM has an asynchronous interface, which means that it responds as quickly as possible to changes in control inputs...
, quickly losing out on grounds of price, and, later on, performance. By the early 2000s, RDRAM was no longer supported by any mainstream computing architecture.
PC main memory
The first PCIBM PC compatible
IBM PC compatible computers are those generally similar to the original IBM PC, XT, and AT. Such computers used to be referred to as PC clones, or IBM clones since they almost exactly duplicated all the significant features of the PC architecture, facilitated by various manufacturers' ability to...
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
DDR SDRAM
Double data rate synchronous dynamic random access memory is a class of memory integrated circuits used in computers. DDR SDRAM has been superseded by DDR2 SDRAM and DDR3 SDRAM, neither of which are either forward or backward compatible with DDR SDRAM, meaning that DDR2 or DDR3 memory modules...
were involved in a standards war. PC-800 RDRAM, which operated at 400 MHz and delivered 1600 MB
Megabyte
The megabyte is a multiple of the unit byte for digital information storage or transmission with two different values depending on context: bytes generally for computer memory; and one million bytes generally for computer storage. The IEEE Standards Board has decided that "Mega will mean 1 000...
/s of bandwidth
Bandwidth (computing)
In computer networking and computer science, bandwidth, network bandwidth, data bandwidth, or digital bandwidth is a measure of available or consumed data communication resources expressed in bits/second or multiples of it .Note that in textbooks on wireless communications, modem data transmission,...
over a 16-bit bus. It was packaged as a 184-pin RIMM (Rambus
Rambus
Rambus Incorporated , founded in 1990, is a technology licensing company. The company became well known for its intellectual property based litigation following the introduction of DDR-SDRAM memory.- History :...
in-line memory module) form factor
Form factor (electronics)
In electronics, the form factor of an alternating current waveform is the ratio of the RMS value to the average value .In case of a sinusoidal wave, i.e...
, similar to a DIMM
DIMM
A DIMM or dual in-line memory module, comprises a series of dynamic random-access memory integrated circuits. These modules are mounted on a printed circuit board and designed for use in personal computers, workstations and servers...
(dual in-line memory module). Data is transferred on both the rising and falling edges of the clock signal, a technique known as DDR
Double data rate
In computing, a computer bus operating with double data rate transfers data on both the rising and falling edges of the clock signal. This is also known as double pumped, dual-pumped, and double transition....
. For marketing reasons the physical clock rate was multiplied by two (because of the DDR operation); therefore, the 400 MHz Rambus standard was named PC-800. This was significantly faster than the previous standard, PC-133 SDRAM
SDRAM
Synchronous dynamic random access memory is dynamic random access memory that is synchronized with the system bus. Classic DRAM has an asynchronous interface, which means that it responds as quickly as possible to changes in control inputs...
, which operated at 133 MHz and delivered 1066 MB/s of bandwidth over a 64-bit bus using a 168-pin DIMM
DIMM
A DIMM or dual in-line memory module, comprises a series of dynamic random-access memory integrated circuits. These modules are mounted on a printed circuit board and designed for use in personal computers, workstations and servers...
form factor.
Moreover, if a mainboard has a dual-
Dual-channel architecture
Multi-channel architecture is a technology that increases the transfer speed of data between the RAM and the memory controller by adding more channels of communication between them. Theoretically this multiplies the data rate by exactly the number of channels present. Dual-channel memory employs...
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 modules.
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 |
Continuity modules
Integrated circuit
An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...
s.
Performance
Compared to other contemporary standards, Rambus shows a significant increase in latency, heat output, manufacturing complexity, and cost. Because of the way Rambus designed RDRAM, RDRAM's die size is inherently larger than similar SDRAM chips. RDRAM's die size is larger because it is required to house the added interface and results in a 10-20 percent price premium at 16-megabit densities and adds about a 5 percent penalty at 64M.http://findarticles.com/p/articles/mi_m0EKF/is_n2161_v43/ai_19288320PC-800 RDRAM operated with a latency of 45 ns
Nanosecond
A nanosecond is one billionth of a second . One nanosecond is to one second as one second is to 31.7 years.The word nanosecond is formed by the prefix nano and the unit second. Its symbol is ns....
, which was more latency than other comparable DRAM technologies of the time. RDRAM memory chips also put out significantly more heat than SDRAM chips, necessitating heatspreaders on all RIMM devices. RDRAM includes a memory controller on each memory chip, significantly increasing manufacturing complexity compared to SDRAM, which used a single memory controller located on the northbridge
Northbridge (computing)
The northbridge has historically been one of the two chips in the core logic chipset on a PC motherboard, the other being the southbridge. Increasingly these functions have migrated to the CPU chip itself, beginning with memory and graphics controllers. For Intel Sandy Bridge and AMD Fusion...
chipset. RDRAM was also two to three times the price of PC-133 SDRAM due to a combination of high manufacturing costs and high license fees. PC-2100 DDR SDRAM
DDR SDRAM
Double data rate synchronous dynamic random access memory is a class of memory integrated circuits used in computers. DDR SDRAM has been superseded by DDR2 SDRAM and DDR3 SDRAM, neither of which are either forward or backward compatible with DDR SDRAM, meaning that DDR2 or DDR3 memory modules...
, 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.
When installing multiple RIMMs on a memory channel, performance impact is greater than SDRAM design because the data in the further memory module has to travel across all memory chips installed physically closer to the memory controller, instead of just 1 or 2 chips in production SDRAM motherboards.
With the introduction of the Intel 840 (Pentium III), Intel 850
Intel 850
The Intel 850 chipset was the first chipset available for the Pentium 4 processor, and was simultaneously released in November 2000. It consists of a 82850 memory controller hub and a 82801BA I/O controller hub....
(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. Then 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. Granite Bay matched i850E + PC-1066 RDRAM bandwidth with considerably lower latency.
To achieve RDRAM's 800 MHz clock rate, the memory module only runs on 16-bit bus, instead of 64-bit bus in contemporary SDRAM DIMM. Furthermore, not all production RDRAM modules at the time of the Intel 820 launch could run at 800 MHz; instead, they ran at a slower clock rate.
Benchmarks
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 440BXIntel 440BX
The Intel 440BX , is a chipset from Intel, supporting Pentium II, Pentium III, and Celeron processors. It is also known as the i440BX and was released in April 1998...
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 2002, benchmarks pointed out that single-channel DDR400 SDRAM modules could closely match dual-channel 1066 MHz RDRAM in everyday applications.
Marketing history
In November 1996, Rambus entered into a development and license contract with Intel. Intel announced to the WintelWintel
Wintel is a portmanteau of Windows and Intel, referring to personal computers using Intel x86 compatible processors running Microsoft Windows...
development community
Community
The term community has two distinct meanings:*a group of interacting people, possibly living in close proximity, and often refers to a group that shares some common values, and is attributed with social cohesion within a shared geographical location, generally in social units larger than a household...
that it would only support the Rambus memory interface for its microprocessor
Microprocessor
A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...
s, Intel was granted rights to purchase 1M shares of Rambus' stock at $10 per share.
As a transition strategy, Intel planned to support PC-100 SDRAM DIMM on future Intel 82x chipsets using Memory Translation Hub (MTH). In 2000, Intel recalled the Intel 820 motherboard with memory translator hub (MTH) because the MTH can, while doing simultaneous switching, produce noise
Electronic noise
Electronic noise is a random fluctuation in an electrical signal, a characteristic of all electronic circuits. Noise generated by electronic devices varies greatly, as it can be produced by several different effects...
that may cause the computer to hang mysteriously or to spontaneously reboot. Since then, no production Intel 820 motherboards contain MTH.
In 2000, Intel subsidized RDRAM by bundling retail boxes of Pentium 4 CPUs with 2 RIMMs. Intel began to phase out Rambus subsidies in 2001.
In 2003, Intel introduced Intel 865 and Intel 875 chipsets, which were marketed as high end replacements of Intel 850. Furthermore, the future memory roadmap did not include Rambus.
Video game consoles
Rambus's RDRAM saw use in three video game consoles, beginning in 1996 with the Nintendo 64Nintendo 64
The , often referred to as N64, was Nintendo′s third home video game console for the international market. Named for its 64-bit CPU, it was released in June 1996 in Japan, September 1996 in North America, March 1997 in Europe and Australia, September 1997 in France and December 1997 in Brazil...
. The Nintendo console utilized 4 MB
Megabyte
The megabyte is a multiple of the unit byte for digital information storage or transmission with two different values depending on context: bytes generally for computer memory; and one million bytes generally for computer storage. The IEEE Standards Board has decided that "Mega will mean 1 000...
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 allows 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 assembly.http://n64.icequake.net/
Sony uses RDRAM in the PlayStation 2
PlayStation 2
The PlayStation 2 is a sixth-generation video game console manufactured by Sony as part of the PlayStation series. Its development was announced in March 1999 and it was first released on March 4, 2000, in Japan...
. The PS2 was equipped with 32 MB of the memory, and implemented a dual-channel configuration resulting in 3200 MB/s available bandwidth. The PlayStation 3
PlayStation 3
The is the third home video game console produced by Sony Computer Entertainment and the successor to the PlayStation 2 as part of the PlayStation series. The PlayStation 3 competes with Microsoft's Xbox 360 and Nintendo's Wii as part of the seventh generation of video game consoles...
utilizes 256 MB of Rambus's XDR DRAM
XDR DRAM
XDR DRAM or extreme data rate dynamic random access memory is a high-performance RAM interface and successor to the Rambus RDRAM it is based on, competing with the rival DDR2 SDRAM and GDDR4 technology. XDR was designed to be effective in small, high-bandwidth consumer systems, high-performance...
, which could be considered a successor to RDRAM, on a 64-bit bus at 400 MHz with an octal data rate (cf. double data rate
Double data rate
In computing, a computer bus operating with double data rate transfers data on both the rising and falling edges of the clock signal. This is also known as double pumped, dual-pumped, and double transition....
) providing a clock rate of 3.2 GHz, allowing a large 204.8 Gbit/s (25.6 GB/s) bandwidth.
Video cards
Cirrus LogicCirrus Logic
Cirrus Logic is a fabless semiconductor supplier specializing in analog, mixed-signal, and audio DSP integrated circuits . They are presently headquartered in Austin, Texas. Their audio processors and audio converters are found in many professional audio and consumer entertainment products,...
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 than competing DRAM technologies with its high bandwidth. The chips were used on the Creative
Creative Technology
Creative Technology Ltd. is a Singapore-based global company headquartered in Jurong East, Singapore. The principal activities of the company and its subsidiaries consist of the design, manufacture and distribution of digitized sound and video boards, computers and related multimedia, and personal...
Graphics Blaster MA3xx series, among others.