Editing SIMM (section)

==History==
SIMMs were invented in 1983 by James E. Clayton<ref name="journal">Clayton, James E. (1983). [https://books.google.com/books?id=mawpAQAAMAAJ&q=SIP Low-cost, high-density memory packaging: A 64K X 9 DRAM SIP module], ''The International journal for hybrid microelectronics''.</ref> at [[Wang Laboratories]] with subsequent patents granted in 1987.<ref>{{US patent|4656605}} - ''Single in-line memory module''</ref>
<ref>{{US patent|4727513}} - ''Signal in-line memory module''</ref> Wang Laboratories [[RAM parity#Wang lawsuit|litigated both patents against multiple companies]].<ref>{{cite web |title=Wang Laboratories, Inc., Plaintiff/cross-appellant, v. Toshiba Corporation; Toshiba America Electronic Components, inc.; Toshiba America Information Systems, Inc., defendants-appellants, and Nec Corporation; Nec Electronics Inc. and Nec Technologies, inc., Defendants-appellants, and Molex Incorporated, Defendant, 993 F.2d 858 (Fed. Cir. 1993)|url=https://law.justia.com/cases/federal/appellate-courts/F2/993/858/310372/|website=justia.com|access-date=22 December 2023|date=May 10, 1993}}</ref><ref>{{cite web |title=Wang Laboratories, Inc., Plaintiff-appellee, v. Clearpoint Research Corporation, Defendant-appellant, 5 F.3d 1504 (Fed. Cir. 1993)|url=https://law.justia.com/cases/federal/appellate-courts/F3/5/1504/626911/|website=justia.com|access-date=22 December 2023|date=July 23, 1993}}</ref><ref>{{cite web |title=Wang Laboratories v. MITSUBISHI ELECTRONICS, 860 F. Supp. 1448 (C.D. Cal. 1993)|url=https://law.justia.com/cases/federal/district-courts/FSupp/860/1448/2159908/|website=justia.com|access-date=22 December 2023|date=December 17, 1993}}</ref><ref>{{cite web |title=Wang Laboratories, Inc., Plaintiff-appellant, v. Mitsubishi Electronics America, Inc. and Mitsubishi Electric Corporation, Defendants/cross-appellants, 103 F.3d 1571 (Fed. Cir. 1997)|url=https://law.justia.com/cases/federal/appellate-courts/F3/103/1571/518294/|website=justia.com|access-date=22 December 2023|date=January 3, 1997}}</ref><ref>{{cite web |title=Wang Laboratories v. OKI ELECTRIC INDUSTRY CO., 15 F. Supp. 2d 166 (D. Mass. 1998)|url=https://law.justia.com/cases/federal/district-courts/FSupp2/15/166/2314770/|website=justia.com|access-date=22 December 2023|date=July 31, 1998}}</ref> The original memory modules were built upon ceramic substrates with 64K Hitachi "flip chip" parts and had pins, i.e. [[single in-line package]] (SIP) [[integrated circuit packaging|packaging]].<ref name="journal" /> SIMMs using pins are usually called [[SIPP memory|SIP or SIPP memory]] modules to distinguish them from the more common modules using edge connectors.

The first variant of SIMMs has 30 pins and provides 8 [[bit]]s of data (plus a 9th error-detection bit in [[Parity bit|parity]] SIMMs). They were used in AT-compatible ([[Intel 80286|286]]-based, e.g., [[Wang APC]]<ref>[https://books.google.com/books?id=xsMx9D2s6y0C&pg=PA33 Wang Plays A Strong PC-Compatible Hand], ''PC Magazine'', October 1, 1985</ref>), [[Intel 80386|386]]-based, [[Intel 80486|486]]-based, [[Macintosh Plus]], [[Macintosh II]], [[Macintosh Quadra|Quadra]], [[Atari STE]] microcomputers, [[Wang VS]] minicomputers and [[Roland Corporation|Roland]] electronic samplers.

The second variant of SIMMs has 72 pins and provides 32 bits of data (36 bits in parity and [[ECC memory|ECC]] versions). These appeared first in the early 1990s in later models of the [[IBM PS/2]], and later in systems based on the [[Intel 80486|486]], [[Intel P5|Pentium]], [[Pentium Pro]], early [[Pentium II]], and contemporary/competing chips of other brands. By the mid-90s, 72-pin SIMMs had replaced 30-pin SIMMs in new-build computers, and were starting to themselves be replaced by [[DIMM]]s.

Non-IBM PC computers such as UNIX [[workstation]]s may use proprietary non-standard SIMMs. The [[Macintosh IIfx]] uses proprietary non-standard SIMMs with 64 pins.

DRAM technologies used in SIMMs include [[dynamic random-access memory#Page mode DRAM|FPM]] (Fast Page Mode memory, used in all 30-pin and early 72-pin modules), and the higher-performance [[dynamic random-access memory#Extended data out DRAM|EDO]] DRAM (used in later 72-pin modules).

Due to the differing data bus widths of the memory modules and some processors, sometimes several modules must be installed in identical pairs or in identical groups of four to fill a memory bank. The rule of thumb is a ''286'', ''386SX'', [[Motorola 68000|68000]] or low-end [[Motorola 68020|68020]] / [[Motorola 68030|68030]] (e.g. Atari Falcon, Mac LC) system (using a 16 bit wide data bus) would require two 30-pin SIMMs for a memory bank. On ''386DX'', ''486'', and full-spec 68020 through [[Motorola 68060|68060]] (e.g. Atari TT, Amiga 4000, Mac II) systems (32 bit data bus), either four 30-pin SIMMs or one 72-pin SIMM are required for one memory bank. On [[Intel P5|Pentium]] systems (data bus width of 64 bits), two 72-pin SIMMs are required. However, some Pentium systems have support for a "half bank mode", in which the data bus would be shortened to only 32 bits to allow operation of a single SIMM. Conversely, some 386 and 486 systems use what is known as "memory interleaving", which requires twice as many SIMMs and effectively doubles the bandwidth.

The earliest SIMM sockets were conventional push-type sockets. These were soon replaced by [[Zero insertion force|ZIF]] sockets in which the SIMM was inserted at an angle, then tilted into an upright position. To remove one, the two metal or plastic clips at each end must be pulled to the side, then the SIMM must be tilted back and pulled out (low-profile sockets reversed this convention somewhat, like SODIMMs - the modules are inserted at a "high" angle, then pushed ''down'' to become more flush with the motherboard). The earlier sockets used plastic retainer clips which were found to break, so steel clips replaced them.

Some SIMMs support [[presence detect]] (PD). Connections are made to some of the pins that encode the capacity and speed of the SIMM, so that compatible equipment can detect the properties of the SIMM. PD SIMMs can be used in equipment which does not support PD; the information is ignored. Standard SIMMs can easily be converted to support PD by fitting jumpers, if the SIMMs have solder pads to do so, or by soldering wires on.<ref>[http://www.keycruncher.com/blog/2003/12/14/making-standard-simm-s-work-memory-upgrade-on-the-hp-laserjet-6mp-5mp/ ''Making Standard SIMMs Work &ndash; Memory Upgrade on the HP LaserJet 6MP/5MP'' Article on fitting jumpers to add Presence Detect to standard SIMMs]</ref>