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== PC main memory == [[File:RAMBUS-Memory.jpg|thumb|upright=1.7|RDRAM memory with integrated heat spreader]] [[File:MR18R0828BN1-CG6.jpg|thumb|upright=1.7|A Samsung RDRAM PC-600 128{{nbsp}}MB]] [[File:RIMM Installed with Pentium 4.jpg|thumb|A Samsung RDRAM Installed with Pentium 4 1.5{{nbsp}}GHz]] The first [[IBM PC compatible|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{{nbsp}}[[MHz]] and delivered 1600{{nbsp}}[[megabyte|MB]]/s of [[bandwidth (computing)|bandwidth]] over a 16-bit bus. It was packaged as a 184-pin '''RIMM''' ([[Rambus]] in-line memory module) [[Form factor (electronics)|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 [[double data rate|DDR]]. To emphasize the advantages of the DDR technique, this type of RAM was marketed at speeds twice the actual clock rate, i.e. 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-channel architecture|dual-]] or [[quad-channel architecture|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 the later 32-bit modules had 232 pins as compared to the older 184-pin 16-bit modules.<ref>[http://www.rdramrambusmemory.com/ rdramrambusmemory.com].</ref> {{clear}} === Module specifications === {| class="wikitable sortable" ! Designation ! Bus width<br>(bits) ! Channels ! Clock rate<br>(MHz) ! Advertised<br>frequency (MHz) ! Bandwidth<br>(MByte/s) |- | PC600 | 16 | Single | 266 | 600 | 1066 |- | PC700 | 16 | Single | 355 | 711 | 1420 |- | PC800 | 16 | Single | 400 | 800 | 1600 |- | PC1066 (RIMM 2100) | 16 | Single | 533 | 1066 | 2133 |- | PC1200 (RIMM 2400) | 16 | Single | 600 | 1200 | 2400 |- | PC800 (RIMM 3200) | 32 (16Γ2) | Dual | 400 | 800 | 3200 |- | PC1066 (RIMM 4200) | 32 (16Γ2) | Dual | 533 | 1066 | 4200 |- | PC1200 (RIMM 4800) | 32 (16Γ2) | Dual | 600 | 1200 | 4800 |- | PC1600 (RIMM 6400) | 32 (16Γ2) | Dual | 800 | 1600 | 6400 |} ==== Continuity modules ==== [[File:RAMBUS-Terminator.jpg|thumb|upright=1.7|A Rambus continuity RIMM (CRIMM), wrongly known as terminator and also known as 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 modules provide no extra memory and only served to propagate the signal to [[electrical termination|termination resistors]] on the motherboard instead of providing a dead end, where signals would reflect. CRIMMs appear physically similar to regular RIMMs, except that they lack [[integrated circuit]]s (and their heat-spreaders). ===Performance=== Compared to other contemporary standards, Rambus showed an 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, resulting in a 10–20% price premium at 16 Mbit densities (adding about a 5% penalty at 64 Mbit).<ref>{{cite web |url=http://www.findarticles.com/p/articles/mi_m0EKF/is_n2161_v43/ai_19288320 |title=Electronic News: Rambus seeks IPO but denies Intel stake - Company Financial Information |website=www.findarticles.com |access-date=12 January 2022 |archive-url=https://web.archive.org/web/20041124045440/http://www.findarticles.com/p/articles/mi_m0EKF/is_n2161_v43/ai_19288320 |archive-date=24 November 2004 |url-status=dead}}</ref> Note that the most common RDRAM densities are 128 Mbit and 256 Mbit. PC-800 RDRAM operated with a latency of 45 [[nanosecond|ns]], more than that of other SDRAM varieties of the time. RDRAM memory chips also put out significantly more heat than SDRAM chips, necessitating [[heatsink|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 more expensive than PC-133 SDRAM due to a combination of higher manufacturing costs and high license fees.{{Citation needed|date=May 2016}} 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 bits. 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. ===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 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 applications.<ref>{{cite web |last=Gavrichenkov |first=Ilya |title=ASUS P4B266 Mainboard Review |url=http://www.xbitlabs.com/articles/mainboards/display/asus-p4b266.html#sect2 |work=Xbit Laboratories |access-date=17 May 2013 |archive-url=https://web.archive.org/web/20160316031942/http://www.xbitlabs.com/articles/mainboards/display/asus-p4b266.html#sect2 |archive-date=2016-03-16 |url-status=dead}}</ref> ===Marketing history=== In November 1996, Rambus entered into a development and license contract with Intel.<ref>[http://www10.edacafe.com/nbc/articles/view_weekly.php?articleid=209198&page_no=3 Memory Continued]. EDACafe Weekly, October 04, 2004.</ref> Intel announced that it would only support the Rambus memory interface for its [[microprocessor]]s<ref>[http://www.webopedia.com/TERM/R/RDRAM.html What is RDRAM?]. Webopedia Computer Dictionary.</ref> and had been granted rights to purchase one million shares of Rambus' stock at $10 per share.<ref>[http://www.stagetools.com/bill/nw978.htm NewsWire Issue 97-8<!-- Bot generated title -->]. {{webarchive|url=https://web.archive.org/web/20160303181832/http://www.stagetools.com/bill/nw978.htm |date=2016-03-03 }}.</ref> As a transition strategy, Intel planned to support PC-100 SDRAM DIMMs on future Intel 82x chipsets using Memory Translation Hub (MTH).<ref>{{cite web |url=https://www.tomshardware.com/reviews/intel-i820-chipset-review,132.html |title=Intel i820 Chipset Review |publisher=Tom's Hardware |date=1999-10-05 |first=Brent |last=Kerby}} .</ref> In 2000, Intel recalled the Intel 820 motherboard, which featured the MTH, due to occasional occurrences of [[Hang (computing)|hanging]] and spontaneous reboots caused by [[Electronic noise|simultaneous switching noise]].<ref>[http://www.computerwriter.com/Star/2000/jun/cw062100_intel_i820_mth_recall.htm cw062100 β Intel i820 MTH recall<!-- Bot generated title -->]. {{webarchive |url=https://web.archive.org/web/20090724162928/http://www.computerwriter.com/Star/2000/jun/cw062100_intel_i820_mth_recall.htm |date=July 24, 2009 }}.</ref> Since then, no production Intel 820 motherboards contain MTH. In 2000, Intel began to subsidize RDRAM by bundling retail boxes of [[Pentium 4]]s with two RIMMs.<ref>[https://web.archive.org/web/20070228204435/http://news.zdnet.com/2100-9595_22-523724.html Intel chips in for cheaper Pentium 4 PCs]. Tech News on ZDNet. .</ref> Intel began to phase out these subsidies in 2001.<ref>[https://archive.today/20120711022039/http://news.com.com/Intel+drops+Rambus+subsidies/2100-1001_3-270561.html Intel drops Rambus subsidies]. CNET News.com.</ref> 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 RDRAM.<ref>{{cite web |url=https://www.tomshardware.com/reviews/ram-wars,610-9.html |title=RAM Wars: Return of the JEDEC |publisher=Tom's Hardware |first=Bruce |last=Gain |date=2003-04-01}}</ref>
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