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RDRAM

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Direct Rambus DRAM or DRDRAM (sometimes just called Rambus DRAM or RDRAM) is a type of synchronous dynamic RAM, designed by the Rambus Corporation.

Implementation

Personal computers

The first PC motherboards with support for RDRAM debuted in 1999. They supported PC-800 RDRAM, which operated at 400 MHz and delivered 1600 MB/s of bandwidth over a 16-bit bus using a 184-pin RIMM form factor. Data is transferred on both the rising and falling edges of the clock signal, a technique known as double data rate. 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.

RDRAM memory with integrated heatsink.

Moreover, if a mainboard has a dual- or quad-channel memory subsystem, all of the memory channels must be upgraded simultaneously. Sixteen-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.

Stick/module specification

  • PC600: 16-bit, single channel RIMM, specified to operate at 300 MHz clock speed, 1200 MB/s bandwidth
  • PC700: 16-bit, single channel RIMM, specified to operate at 355 MHz clock speed, 1420 MB/s bandwidth
  • PC800: 16-bit, single channel RIMM, specified to operate at 400 MHz clock speed, 1600 MB/s bandwidth
  • PC1066 (RIMM 2100): 16-bit, single channel RIMM specified to operate at 533 MHz clock speed, 2133 MB/s bandwidth
  • PC1200 (RIMM 2400): 16-bit, single channel RIMM specified to operate at 600 MHz clock speed, 2400 MB/s bandwidth
  • RIMM 3200: 32-bit, dual channel RIMM specified to operate at 400 MHz clock speed, 3200 MB/s bandwidth
  • RIMM 4200: 32-bit, dual channel RIMM specified to operate at 533 MHz clock speed, 4200 MB/s bandwidth
  • RIMM 4800: 32-bit, dual channel RIMM specified to operate at 600 MHz clock speed, 4800 MB/s bandwidth
  • RIMM 6400: 32-bit, dual channel RIMM specified to operate at 800 MHz clock speed, 6400 MB/s bandwidth

Video game consoles

Rambus's RDRAM saw use in several video game consoles, beginning in 1996 with the Nintendo 64. The Nintendo console utilized 4 MB RDRAM running with a 500 MHz clock on an 8-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.[1]

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 PS3 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[1] (cf. double data rate) providing speeds of 3.2 GHz, allowing a large 204.8 Gbit/s (25.6 GB/s) bandwidth.[2]

Video cards

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 cost-advantage while being potentially faster than competing DRAM technologies with its high bandwidth. The chips were used on the Creative Graphics Blaster MA3xx series, among others.

Performance

Compared to other contemporary standards, Rambus shows a slight increase in latency, heat output, manufacturing complexity, and cost. Some criticized RDRAM's larger die size, which 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.[2]

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.[citation needed] PC-2100 DDR SDRAM, introduced in 2000, operated with a clockspeed 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.

The design of many common Rambus memory controllers dictated that memory sticks be installed in sets of two. Any remaining open memory slots must be filled with 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. The picture on the lower right depicts a CRIMM stick.

A RAMBUS Continuity-RIMM (CRIMM), also known as terminator or dummy.

With the introduction of the i840 (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 i850E chipset, which introduced PC-1066 RDRAM, increasing total dual-channel bandwidth to 4200 MB/s. Then in 2002, Intel released the E7205 Granitebay chipset, which introduced dual-channel DDR support for a total bandwidth of 4200 MB/s, at a slightly lower latency than competing RDRAM.

To achieve RDRAM's 800 MHz speed, the memory module only runs on 16-bit bus, instead of 64-bit bus in contemporary SDRAM DIMM. Furthermore, not all production RDRAM module at the time of Intel 820 launch can run at 800 MHz, but rather at slower speed.

Benchmarks

Benchmark tests conducted in 1998 showed most applications run slower with RDRAM. Although RDRAM was shown to be slightly faster than SDRAM alternatives in UMA solution, Intel 820 was not a low-end product, and no low-end products using RIMM has ever been made, so the advantage is useless for end users.[3]

In 1999, benchmark for Intel 840, Intel 820, Intel 440BX showed the performance gain (if any) from using Rambus chipsets do not justify its premium price over 440BX chipsets with PC-133 SDRAM except for workstation use.[4]

Later in 2002, it was shown that single channel DDR400 SDRAM modules, coupled with SiS648, can closely match against dual channel 1066 MHz RDRAM setup with Intel 850E in real-life applications[5]. Furthermore, there were upcoming chipsets that can use dual channel DDR400 SDRAM modules.

History of RDRAM marketing in PC market

In November, 1996, Rambus entered into a development and license contract with Intel.[3]. Realizing the superiority of RDRAM in comparison to DDR SDRAM, Intel announced to the Wintel development community that it would only support the Rambus memory interface for its microprocessors,[4] Intel was granted rights to purchase 1M shares of Rambus's stock at $10 per share.[5]

In 1998, Intel planned to make a $500 million equity investment in Micron Technology, to accelerate the adoption of Direct RDRAM.[6] Other investment included paying $100 million to Samsung Electronics in 1999.[7]

As a transition strategy, Intel planned to support PC-133 SDRAM DIMM on future Intel 82x chipset using Memory Transfer Hub (MTH).[8] In 2000, Intel recalled 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.[9] Since then, no production Intel 820 motherboards contain MTH.

In 2000, Intel subsidized RDRAM by bundling retail boxes of Pentium 4 CPU with 2 RIMMs.[10] Intel began to phase out Rambus subsidies in 2001.[11]

In 2003, Intel introduced Intel 865 and Intel 875 chipsets, which were marketed as high end replacement of Intel 850. Furthermore, the future memory roadmap did not include Rambus.[12]

Few DRAM manufacturers have ever obtained the license to produce RDRAM, and those who did license the technology failed to make enough RIMMs to satisfy PC market demand, causing RIMM to be priced higher than SDRAM DIMMs, even when memory prices skyrocketed during 2002.[13] During RDRAM's decline, DDR continued to advance in speed while, at the same time, it was still cheaper than RDRAM. Meanwhile, a massive price war in the DDR SDRAM allowed DDR SDRAM to be sold at or below production cost. DDR SDRAM makers were losing massive amounts of money, while RDRAM suppliers were making a good profit for every module sold. While it is still produced today, few motherboards support RDRAM. Between 2002-2005, market share of RDRAM had never extended beyond 5%.[14]

In 2004, it was revealed that Infineon, Hynix, Samsung, Micron, and Elpida had entered into a price-fixing scheme .[15] Infineon, Hynix, Samsung and Elpida all entered plea agreements with the US DOJ, pleading guilty to price fixing over 1999-2002.[16] They paid fines totalling over $700 million and numerous executives were sentenced to jail time.

Rambus has alleged that, as part of the conspiracy, the DRAM manufacturers acted to depress the price of DDR memory in an effort to prevent DRDRAM from succeeding in the market. Those allegations are the subject of lawsuits by Rambus against the various companies.

See also

References

  1. ^ Rambus.com Octal data rate
  2. ^ Rambus.com XDR
  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. ^ HPCwire Article # 14137
  7. ^ Intel Invests In Samsung To Push Rambus
  8. ^ Intel i820 Chipset Review | Tom's Hardware
  9. ^ cw062100 - Intel i820 MTH recall
  10. ^ Intel chips in for cheaper Pentium 4 PCs | Tech News on ZDNet
  11. ^ Intel drops Rambus subsidies - CNET News.com
  12. ^ RAM Wars: Return of the JEDEC | Tom's Hardware
  13. ^ DRAM prices keep rising | Geek.com
  14. ^ RAM Wars: Return of the JEDEC | Tom's Hardware
  15. ^ Government finds witness in RAM price-fixing probe - CNET News.com
  16. ^ See, e.g. http://www.usdoj.gov/atr/cases/samsung.htm, http://www.usdoj.gov/atr/cases/infin.htm, http://www.usdoj.gov/atr/cases/hynix.htm and http://www.usdoj.gov/atr/cases/elpida.htm.
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