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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.
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[edit] Implementation
[edit] 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 raising and the falling edges of the clock signal (double data rate). 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 you have a mainboard with dual or quad channel memory subsystem, you have to upgrade all the channels at once. 16-bit modules provide one channel of memory, while 32-bit ones provide two. Therefore, if you have a dual channel mainboard accepting 16-bit modules, you have to add or remove RIMMs in (matched) pairs. If you have a dual channel mainboard accepting 32-bit modules, you can add or remove single RIMMs as well.
[edit] 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
[edit] 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 MiB 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 RAM 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 MiB of the memory, and implemented a dual-channel configuration resulting in 3200 MB/s available bandwidth. The PS3 utilizes 256 MiB of Rambus's XDR DRAM, which could be considered a successor to RDRAM, on a 64-bit bus at 3.2 GHz, allowing a large 25.6 GB/s bandwidth, again on a relatively narrow data path.
[edit] 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.
[edit] Performance
Compared to other contemporary standards, Rambus shows significantly increased 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, compared to only 7.5 ns for PC-133 SDRAM. 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 chips 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 Rambus memory dictates 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 terminate the other slot. The picture on the lower right depicts a CRIMM stick.
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, but at a much lower latency than competing RDRAM.
To achieve RDRAM's 800MHz 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 800MHz, but rather at slower speed.
[edit] 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 1066MHz RDRAM setup with Intel 850E in real-life applications[5]. Furthermore, there were upcoming chipsets that can use dual channel DDR400 SDRAM modules.
[edit] History of RDRAM marketing in PC market
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In 1996-11, Rambus entered into a development and license contract with Intel.[6]. After Intel had announced to the Wintel development community that it would only support the Rambus memory interface for its microprocessors[7], Intel was granted rights to purchase 1M shares of Rambus's stock at $10 per share.[8]
In 1998, Intel planned to make a $500 million equity investment in Micron Technology, to accelerate the adoption of Direct RDRAM[9]. Other investment included paying $100 million to Samsung Electronics in 1999.[10]
As a transition strategy, Intel planned to support PC-133 SDRAM DIMM on future Intel 82x chipset using Memory Transfer Hub (MTH)[11]. 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.[12] 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.[13] Intel began to phase out Rambus subsidies in 2001.[14]
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.[15]
Few DRAM manufacturers have ever obtained the licence to produce RDRAM, and those who do did license the technology failed to make enough RIMMs to satify PC market demand, causing RIMM to be priced higher than SDRAM DIMMs, even when memory price skyrocketed during 2002.[16] During RDRAM's decline, DDR continued to advance in speed while, at the same time, was still cheaper than RDRAM. While it is still produced today, few motherboards support RDRAM. Between 2002-2005, market share of RDRAM had never gone beyond 5%.[17]
In 2004, it was revealed that Infineon, Hynix, Samsung, Micron, Elpida had entered a price-fixing scheme against Rambus during 2001, to force RDRAM out of the market.[18] The offending parties pleaded guilty and were fined afterwards.
The motive for price-fixing was not officially known, but one theory is that back in the introduction of Intel 820, Intel decided to use RDRAM exclusively on future products, but because of RDRAM's high price, the plan failed. Rambus officials tried to recoup the losses by filing lawsuits against major memory manufacturers starting in year 2000, and claimed SDRAM, DDR SDRAM (and later DDR2, GDDR2, GDDR3 SDRAM) as Rambus's intellectual property, and forcing memory makers into paying royalties. This gave major memory manufacturers motive to drive Rambus and its RDRAM technology out of market.
(برای رسیدن به آرزوهاتون لابه لای داشتن و نداشتن امکاناتتون دست و پا نزنید اراده کنید موفقیت در ذهن شماست رویا است شما از آن واقعیت بسازید ایمان داشته باشید و از فکرتون به جای پولتون استفاده کنید البته به جای فکر به شما پیتزا نمیدن ولی قدرت واقعی رو حتما .)