SIMM

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SIMM

A SIMM, or single in-line memory module, is a type of memory module containing random access memory used in computer

Computer

A computer is a machine that manipulates Data according to a list of Code .The first devices that resemble modern computers date to the mid-20th century , although the computer concept and various machines similar to computers existed earlier....
s from the early 1980s to the late 1990s. It differs from a dual in-line memory module (DIMM), the most predominant form of memory module today, in that the contacts on a SIMM are redundant

Redundancy (engineering)

In engineering, redundancy is the duplication of critical wikt:Components of a system with the intention of increasing reliability of the system, usually in the case of a backup or fail-safe....
on both sides of the module.

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Encyclopedia

A SIMM, or single in-line memory module, is a type of memory module containing random access memory used in computer

Computer

Redundancy (engineering)

JEDEC

JEDEC Solid State Technology Association, formerly known as Joint Electron Device Engineering Council or Joint Electron Device Engineering Councils, is the semiconductor engineering standardization body of the Electronic Industries Alliance , a trade association that represents all areas of the electronics i...
JESD-21C standard.

Most early PC motherboards (8088

Intel 8088

The Intel 8088 is an Intel x86 microprocessor based on the Intel 8086, with 16-bit registers and an 8-bit external data bus. It can address up to 1 megabyte of random access memory....
-based PCs and XT

IBM Personal Computer XT

The IBM Personal Computer XT, often shortened to the IBM XT or simply XT, was IBM's successor to the original IBM Personal Computer....
s) used socketed DIP

Dual in-line package

File:Three_IC_circuit_chips.JPGIn microelectronics, a dual in-line package , sometimes called a DIL package, is an electronic device package with a rectangular housing and two parallel rows of electrical connecting pins....
chips. With the introduction of 286-based PC/AT

IBM Personal Computer/AT

The IBM Personal Computer/AT, more commonly known as the IBM AT and also sometimes called the PC AT or PC/AT, was IBM's second-generation IBM Personal Computer, designed around the 6 MHz Intel 80286 microprocessor and released in 1984 as model number 5170....
s, which could use larger amounts of memory, memory modules evolved to save motherboard space and to ease memory expansion. Instead of plugging in eight or nine single DIP

Dual in-line package

Dram

Dram or DRAM may refer to:* Dram , an imperial unit of mass and volume* Armenian dram, a monetary unit* Dynamic random access memory* Database of Recorded American Music...
chips, only one additional memory module was needed to increase the memory of the computer. A few 286-based computers used (often non-standard) memory modules like SIPP memory

SIPP memory

SIPP was a type of random access memory. Its name stands for Single Inline Plastic Package.It consisted of a small printed circuit board upon which were mounted a number of memory chips....
(single in-line pin package). The SIPP's 30 pins often bent or broke during installation, which is why they were quickly replaced by SIMMs which used contact plates rather than pins.

SIMMs were invented and patented by Wang Laboratories

Wang Laboratories

Wang Laboratories was a computer company founded in 1951 by Dr. An Wang and Dr. G. Y. Chu. The company was successively headquartered in Cambridge, Massachusetts , Tewksbury, Massachusetts , and Lowell, Massachusetts ....
. One of Wang's scientists, James Clayton, invented what was to become the basic memory module, now known as a SIMM (single in-line memory module) in 1983. The first SIMMs appeared on the PS/2

IBM Personal System/2

The Personal System/2 or PS/2 was IBM's third generation of personal computers. The PS/2 line, released to the public in 1987, was created by IBM in an attempt to recapture control of the PC market by introducing an advanced Vendor lock-in architecture....
in the mid 1980s, having been first proposed by Skip Coppola while at IBM. They solved several problems at the time, including shrinking motherboard real estate (they took up much less board space than socketed chips) as well as the effects of rapidly advancing memory capacities (a motherboard would quickly become obsolete based on its sockets for a particular RAM chip capacity) This also allowed the manufacturer (IBM at this time) to source RAM chips from different vendors and in different packaging, yet still allow them to be interchangeable through this intermediate form (the SIMM).

The first variant of SIMMs has 30 pins and provides 8 bit

Bit

A bit is a binary numeral system numerical digit, taking a value of either 0 or 1. Binary digits are a basic unit of information Computer data storage and transmission in digital computing and digital information theory....
s of data (9 bits in parity versions). They were used in 286, 386

Intel 80386

The Intel 80386, otherwise known as the i386 or just 386, is a microprocessor which has been used as the central processing unit of many personal computers and workstations since 1986....
and 486

Intel 80486

The Intel i486, otherwise known as the 80486, was the first tightly pipeline x86 design. Introduced in 1989, it was also the first x86 chip to use more than a million transistors, due to a large on-chip cache and an integrated floating point unit....
systems.

The second variant of SIMMs has 72 pins and provides 32 bits of data (36 bits in parity versions). These appeared on 486, Pentium

Pentium

Pentium Pro

The Pentium Pro is a sixth-generation x86-based microprocessor developed and manufactured by Intel introduced in November 1995. It introduced the Intel P6 and was originally intended to replace the original Pentium in a full range of applications....
and even some Pentium II

Pentium II

The Pentium II brand refers to Intel's sixth-generation microarchitecture and x86 architecture-compatible microprocessors introduced on May 7, 1997....
systems. By the mid 90s, 72-pin SIMMs had replaced 30-pin SIMMs.

Non-IBM PC computers such as UNIX workstation

Workstation

A workstation is a high-end microcomputer designed for technical or scientific applications. Intended primarily to be used by one person at a time, they are commonly connected to a local area network and run multi-user operating systems....
s may use proprietary non-standard SIMMs. The Macintosh IIfx

Macintosh IIfx

The Macintosh IIfx was a model of Apple Macintosh computer, introduced in 1990 as the fastest Mac, and discontinued in 1992. At introduction it cost from US $9,000 to US $12,000, depending on configuration....
use proprietary non-standard SIMMs with 64 pins.

DRAM technologies used in SIMMs include EDO

Dynamic random access memory

Dynamic random access memory is a type of random access memory that stores each bit of data in a separate capacitor within an integrated circuit....
and FPM

Dynamic random access memory

Dynamic random access memory is a type of random access memory that stores each bit of data in a separate capacitor within an integrated circuit....
.

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 general rule of thumb is a 286 or 386SX system (data bus width of 16 bits) would require two 30-pin SIMMs for a memory bank. On 386DX or 486 systems (data bus width of 32 bits), either four 30-pin SIMMs or one 72-pin SIMM are required for one memory bank. On Pentium

Pentium

Introduced on March 22, 1993, the original Pentium was the first superscalar x86 architecture microprocessor. Its fifth-generation x86 microarchitecture was a direct extension of the 80486 architecture with dual integer pipeline s, a faster FPU unit, wider data bus, and features for further reduced address calculation latency....
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 ZIF sockets in which the SIMM was inserted and rotated until it locked into place. To install a SIMM, the module must be placed in the socket at an angle, then rotated (angled) into 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. 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.

Standard sizes available

30-pin SIMM: 256 KB, 1 MB, 4 MB, 16 MB

72-pin SIMM: 1 MB, 2 MB, 4 MB, 8 MB, 16 MB, 32 MB, 64 MB, 128 MB, 256 MB

Standard pinouts

30-pin SIMM Memory Module
Pin #	Nomenclature	Signal Description
1	V_CC
2	CAS	Column Address Strobe
3	DQ1	Data 0
4	A0	Address 0
5	A1	Address 1
6	DQ2	Data 1
7	A2	Address 2
8	A3	Address 3
9	V_SS	Ground
10	DQ3	Data 2
11	A4	Address 4
12	A5	Address 5
13	DQ4	Data 3
14	A6	Address 6
15	A7	Address 7
16	DQ5	Data 4
17	A8	Address 8
18	A9	Address 9
19	A10	Address 10
20	DQ6	Data 5
21	W	Write Enable
22	V_SS	Ground
23	DQ7	Data 6
24	A11	Address 11
25	DQ8	Data 7
26	NC	No Internal Connection
27	RAS	Row Address Strobe
28	NC	No Internal Connection
29	NC	No Internal Connection
30	V_CC

72-pin ECC SIMM Memory Module
Pin #	Non-Parity	Parity	Signal Description
1	V_SS	V_SS	Ground
2	DQ0	DQ0	Data 0
3	DQ1	DQ1	Data 1
4	DQ2	DQ2	Data 2
5	DQ3	DQ3	Data 3
6	DQ4	DQ4	Data 4
7	DQ5	DQ5	Data 5
8	DQ6	DQ6	Data 6
9	DQ7	DQ7	Data 7
10	V_CC	V_CC
11	PD1	PD1	Presence Detect 1
12	A0	A0	Address 0
13	A1	A1	Address 1
14	A2	A2	Address 2
15	A3	A3	Address 3
16	A4	A4	Address 4
17	A5	A5	Address 5
18	A6	A6	Address 6
19	A10	A10	Address 10
20	n/c	PQ8	Data 8 (Parity 1)
21	DQ9	DQ9	Data 9
22	DQ10	DQ10	Data 10
23	DQ11	DQ11	Data 11
24	DQ12	DQ12	Data 12
25	DQ13	DQ13	Data 13
26	DQ14	DQ14	Data 14
27	DQ15	DQ15	Data 15
28	A7	A7	Address 7
29	A11	A11	Address 11
30	V_CC	V_CC
31	A8	A8	Address 8
32	A9	A9	Address 9
33	/RAS3	RAS3	Row Address Strobe 3
34	/RAS2	RAS2	Row Address Strobe 2
35	DQ16	DQ16	Data 16
36	n/c	PQ17	Data 17 (Parity 2)
37	DQ18	DQ18	Data 18
38	DQ19	DQ19	Data 19
39	V_SS	V_SS	Ground
40	/CAS0	CAS0	Column Address Strobe 0
41	/CAS2	CAS2	Column Address Strobe 2
42	/CAS3	CAS3	Column Address Strobe 3
43	/CAS1	CAS1	Column Address Strobe 1
44	/RAS0	RAS0	Row Address Strobe 0
45	/RAS1	RAS1	Row Address Strobe 1
46	A12	A12	Address 12
47	/WE	WE	Read/Write
48	A13	A13	Address 13
49	DQ20	DQ20	Data 20
50	DQ21	DQ21	Data 21
51	DQ22	DQ22	Data 22
52	DQ23	DQ23	Data 23
53	DQ24	DQ24	Data 24
54	DQ25	DQ25	Data 25
55	n/c	PQ26	Data 26 (Parity 3)
56	DQ27	DQ27	Data 27
57	DQ28	DQ28	Data 28
58	DQ29	DQ29	Data 29
59	DQ31	DQ31	Data 31
60	DQ30	DQ30	Data 30
61	V_CC	V_CC
62	DQ32	DQ32	Data 32
63	DQ33	DQ33	Data 33
64	DQ34	DQ34	Data 34
65	n/c	PQ35	Data 35 (Parity 4)
66	PD2	PD2	Presence Detect 2
67	PD3	PD3	Presence Detect 3
68	PD4	PD4	Presence Detect 4
69	PD5	PD5	Presence Detect 5
70	PD6	PD6	Presence Detect 6
71	PD7	PD7	Presence Detect 7
72	V_SS	V_SS	Ground

SIMM

Standard sizes available

Standard pinouts

See also

External links