DIMM: Difference between revisions

Latest revision as of 05:42, 16 November 2025

Two types of DIMMs: a 168-pin SDRAM module (top) and a 184-pin DDR SDRAM module (bottom). The SDRAM module has two notches (rectangular cuts or incisions) on the bottom edge, while the DDR1 SDRAM module has one. Also, each module has eight RAM chips, but the lower one has an unoccupied space for the ninth chip; this space is occupied in ECC DIMMs.

File:Abit-BP6 (cropped) SDRAM DIMM slots.JPG

Three SDRAM DIMM slots on a ABIT BP6 computer motherboard.

A DIMM (Dual In-line Memory Module) is a popular type of memory module used in computers. It is a printed circuit board with one or both sides (front and back) holding DRAM chips and pins.^[1] The vast majority of DIMMs are manufactured in compliance with JEDEC memory standards, although there are proprietary DIMMs. DIMMs come in a variety of speeds and capacities, and are generally one of two lengths: PC, which are Template:Convert, and laptop (SO-DIMM), which are about half the length at Template:Convert.^[2]

History

DIMMs (Dual In-line Memory Module) were a 1990s upgrade for SIMMs (Single In-line Memory Modules)^[3]^[4] as Intel P5-based Pentium processors began to gain market share. The Pentium had a 64-bit bus width, which would require SIMMs installed in matched pairs in order to populate the data bus. The processor would then access the two SIMMs in parallel.

DIMMs were introduced to eliminate this disadvantage. The contacts on SIMMs on both sides are redundant, while DIMMs have separate electrical contacts on each side of the module.^[5] This allowed them to double the SIMMs 32-bit data path into a 64-bit data path.^[6]

The name "DIMM" was chosen as an acronym for Dual In-line Memory Module symbolizing the split in the contacts of a SIMM into two independent rows.^[6] Many enhancements have occurred to the modules in the intervening years, but the word "DIMM" has remained as one of the generic termsTemplate:Clarify for a computer memory module.

Form factors

Widths

DIMMs come in a number of board sizes. In order of descending size: DIMM, SO-DIMM, MiniDIMM, and MicroDIMM.

Regular DIMMs are generally 133.35 mm in length, while SO-DIMMs are generally 67.6 mm in length.^[2]

256 MB MicroDIMM PC133 SDRAM (double sided, 4 chips).

256 MB MicroDIMM PC133 SDRAM (double sided, 4 chips).

SO-DIMM

File:Assorted SO-DIMM Modules (cropped and perspective).jpg

Assorted SO-DIMM Modules

File:DDR SO-DIMM slot PNr°0341.jpg

A DDR SO-DIMM slot on a computer motherboard.

A SO-DIMM (pronounced "so dim" Template:IPAc-en, also spelled SODIMM) or small outline DIMM, is a smaller alternative to a DIMM, being roughly half the physical size of a regular DIMM. The first SO-DIMMs had 72 pins and were introduced by JEDEC in 1997.^[7]^[8]^[9] Before its introduction, many laptops would use proprietary^[10] RAM modules which were expensive and hard to find.^[7]^[11]

SO-DIMMs are often used in computers that have limited space, which include laptops, notebook computers, small-footprint personal computers such as those based on Nano-ITX motherboards, high-end upgradable office printers, and networking hardware such as routers and NAS devices.^[12] They are usually available with the same size data path and speed ratings of the regular DIMMs though normally with smaller capacities.

The original 72-pin SO-DIMM

The original 72-pin SO-DIMM
SO-DIMM SDR 144pin 128MB ram chip by IBM

SO-DIMM SDR 144pin 128MB ram chip by IBM
A 200-pin PC2-5300 DDR2 SO-DIMM.

A 200-pin PC2-5300 DDR2 SO-DIMM.
A 204-pin PC3-10600 DDR3 SO-DIMM.

A 204-pin PC3-10600 DDR3 SO-DIMM.

Connector

File:Laptop SODIMM DDR Memory Comparison V2.svg

A comparison between 200-pin DDR and DDR2 SDRAM SO-DIMMs, and a 204-pin DDR3 SO-DIMM module. They share the same width but differ in pin and notch placement.^[13]

File:16 GiB-DDR4-RAM-Riegel RAM019FIX Small Crop 90 PCNT.png

16 GiB DDR4-2666 1.2 V unbuffered DIMM (UDIMM).

Different generations of memory are not interchangable: neither forward compatible nor backward compatible. To make this difference clear and avoid any confusion, their DIMM modules all have different pin counts and/or different notch positions. DDR5 SDRAM is the most recent type of DDR memory and has been in use since 2020.

DIMM

100-pin: printer SDRAM and printer ROM (e.g., PostScript)
168-pin: SDR SDRAM, sometimes used for FPM/EDO DRAM in workstations or servers, may be 3.3 or 5 V
184-pin: DDR SDRAM
200-pin: FPM/EDO DRAM in some Sun workstations and servers
240-pin: DDR2 SDRAM, DDR3 SDRAM and FB-DIMM DRAM
278-pin: HP high density SDRAM
288-pin: DDR4 SDRAM and DDR5 SDRAM^[14]

SO-DIMM

72-pin: FPM DRAM and EDO DRAM;^[7] different pin configuration from 72-pin SIMM
144-pin: SDR SDRAM,^[7] sometimes used for DDR2 SDRAM
200-pin: DDR SDRAM^[7] and DDR2 SDRAM
204-pin: DDR3 SDRAM
260-pin: DDR4 SDRAM
260-pin: UniDIMMs carrying either DDR3 or DDR4 SDRAM; differently notched than DDR4 SO-DIMMs
262-pin: DDR5 SDRAM

MiniDIMM

244-pin: DDR2 SDRAM

MicroDIMM

144-pin: SDRAM^[7]
172-pin: DDR SDRAM^[7]
214-pin: DDR2 SDRAM

Besides pin count there are also physical notches to differentiate the incompatible types of DIMM. For example, the ancient 168-pin SDR SDRAM had different voltage ratings (5.0 V or 3.3 V) and a difference of registered (buffered) vs unbuffered. As a result it has two notch positions to prevent the insertion of the wrong type of module.

Notch positions on DDR (top) and DDR2 (bottom) DIMM modules.

Notch positions on DDR (top) and DDR2 (bottom) DIMM modules.
4 GB DDR VLP DIMM from Kingston Technology

4 GB DDR VLP DIMM from Kingston Technology

Heights

Several form factors are commonly used in DIMMs. Single Data Rate Synchronous DRAM (SDR SDRAM) DIMMs were primarily manufactured in Template:Convert and Template:Convert heights, with the nominal value being Template:Convert. When 1U rackmount servers started becoming popular, these form factor registered DIMMs had to plug into angled DIMM sockets to fit in the Template:Convert high box. To alleviate this issue, the next standards of DDR DIMMs were created with a "low profile" (LP) height of around Template:Convert. These fit into vertical DIMM sockets for a 1U platform.

With the advent of blade servers, angled slots have once again become common in order to accommodate LP form factor DIMMs in these space-constrained boxes. This led to the development of the Very Low Profile (VLP) form factor DIMM with a height of around Template:Convert. These will fit vertically in ATCA systems.

Very similar height levels are used for SO-DIMM, Mini-DIMM and Micro-DIMM.^[15]

JEDEC standard heights for DIMMs^[16]
Generation	Full-height (1U)		Very low profile (VLP)		Notes
Generation	Nominal	Maximum	Nominal	Maximum	Notes
DDR2^[17]	Template:Convert	Template:Convert	Template:N/A	Template:N/A
DDR3^[18]	Template:Convert	Template:Convert	Template:Convert	Template:Convert
DDR4^[19]	Template:Convert	Template:Convert	Template:Convert	Template:Convert
DDR5^[20]	Template:Convert	Template:Convert	Template:N/A	Template:N/A	For DIMMs, there is a new height called 2U DIMM at Template:Convert nominal and Template:Convert max. DDR5 and LPDDR5 also use CAMM2 units. These are mounted flush to the motherboard.

Notes:

Low profile (LP) is not a JEDEC standard.
The full JEDEC standards also regulate factors such as thickness.
SO-DIMMs for DDR4 and DDR5 maintain the traditional height of Template:Val mm; see JEDEC MO-310A and MO-337B. The height increase for "full height" DIMM does not apply to SO-DIMM.
It is common for higher-end consumer DDR4 DIMMs to exceed the JEDEC full height due to the use of an added heat sink. Some heat sinks add as little as Template:Convert while others add up to Template:Convert.

Similar connectors

As of Q2 2017, Asus has had a PCIe based "DIMM.2", which has a similar socket to DDR3 DIMMs and is used to put in a module to connect up to two M.2 NVMe solid-state drives. However, it cannot use common DDR type ram and does not have much support from other than Asus.^[21]

Components

Organization

Most DIMMs are built using "×4" ("by four") or "×8" ("by eight") memory chips with up to nine chips per side; "×4" and "×8" refer to the data width of the DRAM chips in bits. High-capacity DIMMs such as 256 GB DIMMs can have up to 19 chips per side.

In the case of "×4" registered DIMMs, the data width per side is 36 bits; therefore, the memory controller (which requires 72 bits) needs to address both sides at the same time to read or write the data it needs. In this case, the two-sided module is single-ranked. For "×8" registered DIMMs, each side is 72 bits wide, so the memory controller only addresses one side at a time (the two-sided module is dual-ranked).

The above example applies to ECC memory that stores 72 bits instead of the more common 64. There would also be one extra chip per group of eight, which is not counted.

Ranking

Script error: No such module "Labelled list hatnote". Sometimes, memory modules are designed with two or more independent sets of DRAM chips connected to the same address and data buses; each such set is called a rank. Of the ranks that share the same memory slot, i.e. on the same module, only one rank may be accessed at any given time. The rank to be accessed is specified by activating its chip select (CS) signal, while the other ranks on the same module are deactivated for the duration of the operation by having their corresponding CS signals deactivated.

After a memory word is fetched, the memory is typically inaccessible for an extended period of time while the sense amplifiers are charged for access of the next cell. These amplifiers typically have 3 cycles of idle time for recharging between accesses. By interleaving the memory (e.g. cells 0, 4, 8, ... are stored in one rank, cells 1, 5, 9, ... in another rank, and so on), sequential memory accesses can be performed more rapidly by alternating which rank is active, thus overlapping the active memory access with recharge time for the inactive ranks.

Template:As of, DIMMs are commonly manufactured with one, two, or four ranks per module. Consumer DIMM vendors have began to distinguish between single- and dual-ranked DIMMs since around 2020.

DIMMs are often referred to as "single-sided" or "double-sided" to describe whether the DRAM chips are located on one or both sides of the module's printed circuit board (PCB). However, these terms may cause confusion, as the physical layout of the chips does not necessarily relate to how they are logically organized or accessed. Indeed, quad-ranked DIMMs exist.

JEDEC decided that the terms "dual-sided", "double-sided", or "dual-banked" were not correct when applied to registered DIMMs (RDIMMs).

Multiplexed Rank DIMM (MRDIMM) allow data from multiple ranks to be transmitted on the same channel. It was announced for DDR5 in July 2024 and is expected to be backwards compatible with DDR5 RDIMM.^[22]

SPD EEPROM

A DIMM's capacity and other operational parameters may be identified with serial presence detect (SPD), an additional chip which contains information about the module type and timing for the memory controller to be configured correctly. The SPD EEPROM connects to the System Management Bus and may also contain thermal sensors (TS-on-DIMM).^[23]

Features

Speeds

For various technologies, there are certain bus and device clock frequencies that are standardized; there is also a decided nomenclature for each of these speeds for each type.

DIMMs based on Single Data Rate (SDR) DRAM have the same bus frequency for data, address and control lines. DIMMs based on Double Data Rate (DDR) DRAM have data but not the strobe at double the rate of the clock; this is achieved by clocking on both the rising and falling edge of the data strobes. Power consumption and voltage gradually became lower with each generation of DDR-based DIMMs.

Another influence is Column Access Strobe (CAS) latency, or CL, which affects memory access speed. This is the delay time between the READ command and the moment data is available. See main article CAS/CL and memory timing.

Template:Col-float Template:Table alignment

SDR SDRAM DIMMs
Chip	Module	Effective clock (MHz)	Transfer rate (MT/s)	Voltage (V)
SDR-66	PC-66	66	66	3.3
SDR-100	PC-100	100	100	3.3
SDR-133	PC-133	133	133	3.3

Template:Table alignment

DDR SDRAM (DDR1) DIMMs
Chip	Module	Memory clock (MHz)	I/O bus clock (MHz)	Transfer rate (MT/s)	Voltage (V)
DDR-200	PC-1600	100	100	200	2.5
DDR-266	PC-2100	133	133	266	2.5
DDR-333	PC-2700	166	166	333	2.5
DDR-400	PC-3200	200	200	400	2.6

Template:Table alignment

DDR2 SDRAM DIMMs
Chip	Module	Memory clock (MHz)	I/O bus clock (MHz)	Transfer rate (MT/s)	Voltage (V)
DDR2-400	PC2-3200	100	200	400	1.8
DDR2-533	PC2-4200	133	266	533	1.8
DDR2-667	PC2-5300	166	333	667	1.8
DDR2-800	PC2-6400	200	400	800	1.8
DDR2-1066	PC2-8500	266	533	1066	1.8

Template:Col-float-break

Template:Table alignment

DDR3 SDRAM DIMMs
Chip	Module	Memory clock (MHz)	I/O bus clock (MHz)	Transfer rate (MT/s)	Voltage (V)
DDR3-800	PC3-6400	100	400	800	1.5
DDR3-1066	PC3-8500	133	533	1066	1.5
DDR3-1333	PC3-10600	166	667	1333	1.5
DDR3-1600	PC3-12800	200	800	1600	1.5
DDR3-1866	PC3-14900	233	933	1866	1.5
DDR3-2133	PC3-17000	266	1066	2133	1.5
DDR3-2400	PC3-19200	300	1200	2400	1.5

Template:Table alignment

DDR4 SDRAM DIMMs
Chip	Module	Memory clock (MHz)	I/O bus clock (MHz)	Transfer rate (MT/s)	Voltage (V)
DDR4-1600	PC4-12800	200	800	1600	1.2
DDR4-1866	PC4-14900	233	933	1866	1.2
DDR4-2133	PC4-17000	266	1066	2133	1.2
DDR4-2400	PC4-19200	300	1200	2400	1.2
DDR4-2666	PC4-21300	333	1333	2666	1.2
DDR4-3200	PC4-25600	400	1600	3200	1.2

Template:Table alignment

DDR5 SDRAM DIMMs
Chip	Module	Memory clock (MHz)	I/O bus clock (MHz)	Transfer rate (MT/s)	Voltage (V)
DDR5-4000	PC5-32000	2000	2000	4000	1.1
DDR5-4400	PC5-35200	2200	2200	4400	1.1
DDR5-4800	PC5-38400	2400	2400	4800	1.1
DDR5-5200	PC5-41600	2600	2600	5200	1.1
DDR5-5600	PC5-44800	2800	2800	5600	1.1
DDR5-6000	PC5-48000	3000	3000	6000	1.1
DDR5-6200	PC5-49600	3100	3100	6200	1.1
DDR5-6400	PC5-51200	3200	3200	6400	1.1
DDR5-6800	PC5-54400	3400	3400	6800	1.1
DDR5-7200	PC5-57600	3600	3600	7200	1.1
DDR5-7600	PC5-60800	3800	3800	7600	1.1
DDR5-8000	PC5-64000	4000	4000	8000	1.1
DDR5-8400	PC5-67200	4200	4200	8400	1.1
DDR5-8800	PC5-70400	4400	4400	8800	1.1

Template:Col-float-end

Error correction

ECC DIMMs are those that have extra data bits which can be used by the system memory controller to detect and correct errors. There are numerous ECC schemes, but perhaps the most common is Single Error Correct, Double Error Detect (SECDED) which uses an extra byte per 64-bit word. ECC modules usually carry a multiple of 9 instead of a multiple of 8 chips as a result.

Register/buffer

It is electrically demanding for a memory controller to drive many DIMMs. Registered DIMMs add a hardware register to the clock, address, and command lines so that the signals are refreshed on the DIMM, allowing a reduced load on the memory controller. Variants include LRDIMM with all lines buffered and CUDIMM/CSODIMM with only the clock signal buffered. The register feature often occurs with ECC, but they do not actually depend on each other and can occur independently.

References

Template:Reflist

External links

Template:Sister project

Template:DRAM

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↑ JEDEC documents MO-256, MO-260, MO-274
↑ JEDEC MO-269J Whitepaper., accessed Aug. 20, 2014.
↑ JEDEC MO-309E Whitepaper., accessed Aug. 20, 2014.
↑ DIMM:MO-329J; SO-DIMM: MO-337B.
↑ ASUS DIMM.2 is a M.2 Riser Card. Template:Webarchive, accessed Jun. 4, 2020.
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[17] JEDEC documents MO-256, MO-260, MO-274

[18] JEDEC MO-269J Whitepaper., accessed Aug. 20, 2014.

[19] JEDEC MO-309E Whitepaper., accessed Aug. 20, 2014.

[20] DIMM:MO-329J; SO-DIMM: MO-337B.

[21] ASUS DIMM.2 is a M.2 Riser Card. Template:Webarchive, accessed Jun. 4, 2020.

[22] Script error: No such module "citation/CS1".

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@@ Line 1: / Line 1: @@
 {{Short description|Computer memory module}}
-[[File:168 pin and 184 pin DIMM.jpg|thumb|Two types of DIMMs: a 168-pin [[SDRAM]] module (top) and a 184-pin [[DDR SDRAM]] module (bottom). The SDRAM module has two notches (rectangular cuts or incisions) on the bottom edge, while the DDR1 SDRAM module has one. Also, each module has eight RAM chips, but the lower one has an unoccupied space for the ninth chip; this space is occupied in [[ECC_memory|ECC]] DIMMs.]]
+[[File:168 pin and 184 pin DIMM.jpg|thumb|Two types of DIMMs: a 168-pin [[SDRAM]] module (top) and a 184-pin [[DDR SDRAM]] module (bottom). The SDRAM module has two notches (rectangular cuts or incisions) on the bottom edge, while the DDR1 SDRAM module has one. Also, each module has eight RAM chips, but the lower one has an unoccupied space for the ninth chip; this space is occupied in [[ECC memory|ECC]] DIMMs.]]
 [[File:Abit-BP6 (cropped) SDRAM DIMM slots.JPG|thumb|upright=1.6|Three [[SDRAM]] DIMM slots on a [[ABIT BP6]] computer motherboard.]]
-A '''DIMM''' ('''Dual In-line Memory Module''') is a popular type of [[memory module]] used in computers. It is a [[printed circuit board]] with one or both sides (front and back) holding [[DRAM]] [[integrated circuit|chip]]s and [[Pin (electronics)|pin]]s.<ref name="GeeksforGeeks 2020 e240">{{cite web | title=What is DIMM(Dual Inline Memory Module)? | website=GeeksforGeeks | date=2020-04-15 | url=https://www.geeksforgeeks.org/what-is-dimmdual-inline-memory-module/ | access-date=2024-04-07 | quote=In the case of SIMM, the connectors are only present on the single side of the module...DIMM has a row of connectors on both sides(front and back) of the module | archive-date=2024-04-07 | archive-url=https://web.archive.org/web/20240407102508/https://www.geeksforgeeks.org/what-is-dimmdual-inline-memory-module/ | url-status=live }}</ref> The vast majority of DIMMs are manufactured in compliance with [[JEDEC memory standards]], although there are proprietary DIMMs. DIMMs come in a variety of speeds and capacities, and are generally one of two lengths: PC, which are {{Convert|133.35|mm|in|2|abbr=on}}, and laptop (SO-DIMM), which are about half the length at {{Convert|67.60|mm|in|2|abbr=on}}.<ref name=":0" />
+A '''DIMM''' ('''Dual In-line Memory Module''') is a popular type of [[memory module]] used in computers. It is a [[printed circuit board]] with one or both sides (front and back) holding [[DRAM]] [[integrated circuit|chip]]s and [[Pin (electronics)|pin]]s.<ref name="GeeksforGeeks 2020 e240">{{cite web |title=What is DIMM (Dual Inline Memory Module)?  |website=GeeksforGeeks |date=2020-04-15 |url=https://www.geeksforgeeks.org/what-is-dimmdual-inline-memory-module/ |access-date=2024-04-07 |quote=In the case of SIMM, the connectors are only present on the single side of the module...DIMM has a row of connectors on both sides(front and back) of the module |archive-date=2024-04-07 |archive-url=https://web.archive.org/web/20240407102508/https://www.geeksforgeeks.org/what-is-dimmdual-inline-memory-module/ |url-status=live }}</ref> The vast majority of DIMMs are manufactured in compliance with [[JEDEC memory standards]], although there are proprietary DIMMs. DIMMs come in a variety of speeds and capacities, and are generally one of two lengths: PC, which are {{Convert|133.35|mm|in|2|abbr=on}}, and laptop (SO-DIMM), which are about half the length at {{Convert|67.60|mm|in|2|abbr=on}}.<ref name=":0" />
 == History ==
-DIMMs (Dual In-line Memory Module) were a 1990s upgrade for [[SIMM]]s (Single In-line Memory Modules)<ref>{{cite book | url=https://books.google.com/books?id=zWrZY1OgTPsC&dq=dimm+simm+ram&pg=PA576 | title=The X86 Microprocessors: Architecture and Programming (8086 to Pentium) | isbn=9788131732465 | last1=Lyla | first1=Das B. | date=September 2010 | publisher=Pearson Education India }}</ref><ref>{{Cite book|url=https://books.google.com/books?id=gXaRdKyD4PsC&dq=so+dimm+1995&pg=PA334|title=Upgrading and Repairing PCs: Upgrading and Repairing_c21|first=Scott|last=Mueller|date=March 7, 2013|publisher=Que Publishing|isbn=9780133105360|via=Google Books|access-date=December 26, 2023|archive-date=September 17, 2024|archive-url=https://web.archive.org/web/20240917213349/https://books.google.com/books?id=gXaRdKyD4PsC&dq=so+dimm+1995&pg=PA334#v=onepage&q=so%20dimm%201995&f=false|url-status=live}}</ref> as [[Intel]] [[P5 (microarchitecture)|P5]]-based [[Pentium]] processors began to gain market share. The Pentium had a 64-bit [[bus (computing)|bus]] width, which would require SIMMs installed in matched pairs in order to populate the data bus. The processor would then access the two SIMMs in parallel.
+DIMMs (Dual In-line Memory Module) were a 1990s upgrade for [[SIMM]]s (Single In-line Memory Modules)<ref>{{cite book | url=https://books.google.com/books?id=zWrZY1OgTPsC&dq=dimm+simm+ram&pg=PA576 | title=The X86 Microprocessors: Architecture and Programming (8086 to Pentium) | isbn=978-81-317-3246-5 | last1=Lyla | first1=Das B. | date=September 2010 | publisher=Pearson Education India }}</ref><ref>{{Cite book|url=https://books.google.com/books?id=gXaRdKyD4PsC&dq=so+dimm+1995&pg=PA334|title=Upgrading and Repairing PCs: Upgrading and Repairing_c21|first=Scott|last=Mueller|date=March 7, 2013|publisher=Que Publishing|isbn=978-0-13-310536-0|via=Google Books|access-date=December 26, 2023|archive-date=September 17, 2024|archive-url=https://web.archive.org/web/20240917213349/https://books.google.com/books?id=gXaRdKyD4PsC&dq=so+dimm+1995&pg=PA334#v=onepage&q=so%20dimm%201995&f=false|url-status=live}}</ref> as [[Intel]] [[P5 (microarchitecture)|P5]]-based [[Pentium]] processors began to gain market share. The Pentium had a 64-bit [[bus (computing)|bus]] width, which would require SIMMs installed in matched pairs in order to populate the data bus. The processor would then access the two SIMMs in parallel.
-DIMMs were introduced to eliminate this disadvantage. The contacts on SIMMs on both sides are redundant, while DIMMs have separate electrical contacts on each side of the module.<ref>{{cite book | url=https://books.google.com/books?id=SrP3aWed-esC | title=Memory Systems: Cache, DRAM, Disk | isbn=9780080553849 | last1=Jacob | first1=Bruce | last2=Wang | first2=David | last3=Ng | first3=Spencer | date=28 July 2010 | publisher=Morgan Kaufmann }}</ref> This allowed them to double the SIMMs 32-bit data path into a 64-bit data path.<ref name="auto1">{{cite book | url=https://books.google.com/books?id=E1p2FDL7P5QC&dq=simm+32+bits+dimm+64+bits&pg=PA442 | title=Upgrading and Repairing PCS | isbn=9780789729743 | last1=Mueller | first1=Scott | date=2004 | publisher=Que | access-date=2023-12-26 | archive-date=2024-09-17 | archive-url=https://web.archive.org/web/20240917213304/https://books.google.com/books?id=E1p2FDL7P5QC&dq=simm+32+bits+dimm+64+bits&pg=PA442#v=onepage&q=simm%2032%20bits%20dimm%2064%20bits&f=false | url-status=live }}</ref>
+DIMMs were introduced to eliminate this disadvantage. The contacts on SIMMs on both sides are redundant, while DIMMs have separate electrical contacts on each side of the module.<ref>{{cite book | url=https://books.google.com/books?id=SrP3aWed-esC | title=Memory Systems: Cache, DRAM, Disk | isbn=978-0-08-055384-9 | last1=Jacob | first1=Bruce | last2=Wang | first2=David | last3=Ng | first3=Spencer | date=28 July 2010 | publisher=Morgan Kaufmann }}</ref> This allowed them to double the SIMMs 32-bit data path into a 64-bit data path.<ref name="auto1">{{cite book | url=https://books.google.com/books?id=E1p2FDL7P5QC&dq=simm+32+bits+dimm+64+bits&pg=PA442 | title=Upgrading and Repairing PCS | isbn=978-0-7897-2974-3 | last1=Mueller | first1=Scott | date=2004 | publisher=Que | access-date=2023-12-26 | archive-date=2024-09-17 | archive-url=https://web.archive.org/web/20240917213304/https://books.google.com/books?id=E1p2FDL7P5QC&dq=simm+32+bits+dimm+64+bits&pg=PA442#v=onepage&q=simm%2032%20bits%20dimm%2064%20bits&f=false | url-status=live }}</ref>
 The name "DIMM" was chosen as an acronym for ''Dual In-line Memory Module'' symbolizing the split in the contacts of a SIMM into two independent rows.<ref name="auto1"/> Many enhancements have occurred to the modules in the intervening years, but the word "DIMM" has remained as one of the generic terms{{clarify|date=March 2025}} for a computer memory module.
-== Variants ==
+== Form factors ==
-[[File:THL32V1055BTG-6.jpg|thumb|72-pin SO-DIMM]]
+=== Widths ===
-There are numerous DIMM variants, employing different pin-counts:
+DIMMs come in a number of board sizes. In order of descending size: DIMM, SO-DIMM, MiniDIMM, and MicroDIMM.
+Regular DIMMs are generally 133.35&nbsp;mm in length, while SO-DIMMs are generally 67.6&nbsp;mm in length.<ref name=":0">{{cite web |url=https://www.simmtester.com/News/PublicationArticle/168 |date=2009-10-06 |access-date=2021-05-13 |title=Common DIMM Memory Form Factor |archive-date=2021-05-13 |archive-url=https://web.archive.org/web/20210513093518/https://www.simmtester.com/News/PublicationArticle/168 |url-status=live }}</ref>
+<gallery>
+File:Nanonote 03 2.jpg|256&nbsp;MB MicroDIMM PC133 SDRAM (double sided, 4 chips).
+</gallery>
+==== SO-DIMM ====
+[[File:Assorted SO-DIMM Modules (cropped and perspective).jpg|thumb|Assorted SO-DIMM Modules]]
+[[File:DDR_SO-DIMM_slot_PNr°0341.jpg|thumb|A DDR SO-DIMM slot on a computer [[motherboard]].]]
+A '''SO-DIMM''' (pronounced "so dim" {{IPAc-en|ˈ|s|oʊ|d|ɪ|m}}, also spelled '''SODIMM''') or '''small outline DIMM''', is a smaller alternative to a DIMM, being roughly half the physical size of a regular DIMM. The first SO-DIMMs had 72 pins and were introduced by JEDEC in 1997.<ref name="auto"/><ref>{{cite web |url=https://www.jedec.org/standards-documents/docs/module-444 |title=72 Pin DRAM SO-DIMM &#124; JEDEC |access-date=2023-11-09 |archive-date=2024-09-17 |archive-url=https://web.archive.org/web/20240917213306/https://www.jedec.org/standards-documents/docs/module-444 |url-status=live }}</ref><ref>{{Cite web|url=http://archive.org/details/completeidiotsgu00fult|title=The complete idiot's guide to upgrading and repairing PCs|first=Jennifer|last=Fulton|date=November 9, 2000|publisher=Indianapolis, IN : Alpha Books|via=Internet Archive}}</ref> Before its introduction, many laptops would use proprietary<ref>{{Cite web|url=https://books.google.com/books?id=u2cfcECC1dwC&dq=%2260-pin%22+memory+card&pg=PP36|title=PC Magazine|last1=Jones|first1=Mitt|date=December 25, 1990|publisher=Ziff-Davis Publishing Company|via=Google Books|access-date=February 4, 2024|archive-date=September 17, 2024|archive-url=https://web.archive.org/web/20240917213428/https://books.google.com/books?id=u2cfcECC1dwC&dq=%2260-pin%22+memory+card&pg=PP36#v=onepage&q=%2260-pin%22%20memory%20card&f=false|url-status=live}}</ref> RAM modules which were expensive and hard to find.<ref name="auto"/><ref>{{cite book |url=https://books.google.com/books?id=O0FTac_k7CIC&dq=laptop+proprietary+sodimm&pg=PA36 |title=Peter Norton's New Inside the PC |isbn=978-0-672-32289-1 |last1=Norton |first1=Peter |last2=Clark |first2=Scott H. |date=2002 |publisher=Sams }}</ref>
+SO-DIMMs are often used in computers that have limited space, which include [[laptop]]s, [[notebook computer]]s, small-footprint personal computers such as those based on [[Nano-ITX motherboard]]s, high-end upgradable office [[Computer printer|printers]], and [[networking hardware]] such as [[Router (computing)|routers]] and [[Network-attached storage|NAS]] devices.<ref>{{cite web |author=Synology Inc. |title=Synology RAM Module |url=https://www.synology.com/en-global/products/Synology_RAM_Module |work=synology.com |access-date=2022-03-23 |archive-date=2016-06-02 |archive-url=https://web.archive.org/web/20160602224830/https://www.synology.com/en-global/products/Synology_RAM_Module |url-status=live }}</ref> They are usually available with the same size data path and speed ratings of the regular DIMMs though normally with smaller capacities.
+<gallery>
+File:THL32V1055BTG-6.jpg|The original 72-pin SO-DIMM
+File:IBM_SO-DIMM_ram_128mb.jpg|SO-DIMM SDR 144pin 128MB ram chip by IBM
+File:Samsung-1GB-DDR2-Laptop-RAM.jpg|A 200-pin [[PC2-5300]] DDR2 SO-DIMM.
+File:4GB_DDR3_SO-DIMM.jpg|A 204-pin PC3-10600 DDR3 SO-DIMM.
+</gallery>
+=== Connector ===
+[[File:Laptop_SODIMM_DDR_Memory_Comparison_V2.svg|thumb|A comparison between 200-pin DDR and DDR2 SDRAM SO-DIMMs, and a 204-pin DDR3 SO-DIMM module. They share the same width but differ in pin and notch placement.<ref name="custhelp">{{cite web |url=http://acer.custhelp.com/app/answers/detail/a_id/2178/~/are-ddr,-ddr2-and-ddr3-so-dimm-memory-modules-interchangeable%3F |title=Are DDR, DDR2 and DDR3 SO-DIMM memory modules interchangeable? |access-date=2015-06-26 |website = acer.custhelp.com}}{{Dead link|date=September 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>]]
+[[File:16 GiB-DDR4-RAM-Riegel RAM019FIX Small Crop 90 PCNT.png|thumb|16&nbsp;GiB DDR4-2666 1.2&nbsp;V [[UDIMM|unbuffered DIMM (UDIMM)]].]]
+Different generations of memory are not interchangable: neither [[forward compatible]] nor [[backward compatible]]. To make this difference clear and avoid any confusion, their DIMM modules all have different pin counts and/or different notch positions. DDR5 SDRAM is the most recent type of DDR memory and has been in use since 2020.
 ;DIMM
@@ Line 23: / Line 49: @@
 :* 240-pin: [[DDR2 SDRAM]], [[DDR3 SDRAM]] and [[FB-DIMM]] DRAM
 :* 278-pin: [[Hewlett-Packard|HP]] high density SDRAM
-:* 288-pin: [[DDR4 SDRAM]] and [[DDR5 SDRAM]]<ref name="anandtech-ddr5">{{cite web|url=https://www.anandtech.com/show/15912/ddr5-specification-released-setting-the-stage-for-ddr56400-and-beyond|title=DDR5 Memory Specification Released: Setting the Stage for DDR5-6400 And Beyond|last=Smith|first=Ryan|date=2020-07-14|website=AnandTech|access-date=2020-07-15|archive-date=2021-04-05|archive-url=https://web.archive.org/web/20210405133714/https://www.anandtech.com/show/15912/ddr5-specification-released-setting-the-stage-for-ddr56400-and-beyond|url-status=live}}</ref>
+:* 288-pin: [[DDR4 SDRAM]] and [[DDR5 SDRAM]]<ref name="anandtech-ddr5">{{cite web|url=https://www.anandtech.com/show/15912/ddr5-specification-released-setting-the-stage-for-ddr56400-and-beyond|title=DDR5 Memory Specification Released: Setting the Stage for DDR5-6400 And Beyond|last=Smith|first=Ryan|date=2020-07-14|website=AnandTech|access-date=2020-07-15|archive-date=2021-04-05|archive-url=https://web.archive.org/web/20210405133714/https://www.anandtech.com/show/15912/ddr5-specification-released-setting-the-stage-for-ddr56400-and-beyond}}</ref>
 ;SO-DIMM
-:* {{0}}72-pin: FPM DRAM and EDO DRAM;<ref name="auto">{{cite book | url=https://books.google.com/books?id=xCXVGneKwScC | title=Upgrading and Repairing Laptops | isbn=9780789728005 | last1=Mueller | first1=Scott | date=2004 | publisher=Que | access-date=2023-12-26 | archive-date=2024-09-17 | archive-url=https://web.archive.org/web/20240917213427/https://books.google.com/books?id=xCXVGneKwScC | url-status=live }}</ref> different pin configuration from 72-pin SIMM
+:* {{0}}72-pin: FPM DRAM and EDO DRAM;<ref name="auto">{{cite book |url=https://books.google.com/books?id=xCXVGneKwScC |title=Upgrading and Repairing Laptops |isbn=978-0-7897-2800-5 |last1=Mueller |first1=Scott |date=2004 |publisher=Que |access-date=2023-12-26 |archive-date=2024-09-17 |archive-url=https://web.archive.org/web/20240917213427/https://books.google.com/books?id=xCXVGneKwScC |url-status=live }}</ref> different pin configuration from 72-pin SIMM
 :* 144-pin: SDR SDRAM,<ref name="auto"/> sometimes used for [[DDR2 SDRAM]]
 :* 200-pin: DDR SDRAM<ref name="auto"/> and DDR2 SDRAM
@@ Line 34: / Line 60: @@
 ;MiniDIMM
 :* 244-pin: DDR2 SDRAM
-[[File:Nanonote 03 2.jpg|thumb|256&nbsp;MB MicroDIMM PC133 SDRAM (double sided, 4 chips).]]
 ;MicroDIMM
 :* 144-pin: SDRAM<ref name="auto"/>
@@ Line 40: / Line 65: @@
 :* 214-pin: DDR2 SDRAM
-== SO-DIMM ==
+Besides pin count there are also physical notches to differentiate the incompatible types of DIMM. For example, the ancient 168-pin SDR SDRAM had different voltage ratings (5.0&nbsp;V or 3.3&nbsp;V) and a difference of [[Registered memory|registered (buffered)]] vs [[Unbuffered memory|unbuffered]]. As a result it has two notch positions to prevent the insertion of the wrong type of module.
-[[File:Assorted SO-DIMM Modules.jpg|thumb|Assorted SO-DIMM Modules]]
-[[File:Samsung-1GB-DDR2-Laptop-RAM.jpg|thumb|A 200-pin [[PC2-5300]] DDR2 SO-DIMM.]]
-[[File:4GB_DDR3_SO-DIMM.jpg|thumb|A 204-pin PC3-10600 DDR3 SO-DIMM.]]
-[[File:DDR_SO-DIMM_slot_PNr°0341.jpg|thumb|upright=1.6|A SO-DIMM slot on a computer [[motherboard]].]]
-A '''SO-DIMM''' (pronounced "so dim" {{IPAc-en|ˈ|s|oʊ|d|ɪ|m}}, also spelled '''SODIMM''') or '''small outline DIMM''', is a smaller alternative to a DIMM, being roughly half the physical size of a regular DIMM. The first SO-DIMMs had 72 pins and were introduced by JEDEC in 1997.<ref name="auto"/><ref>{{cite web | url=https://www.jedec.org/standards-documents/docs/module-444 | title=72 Pin DRAM SO-DIMM &#124; JEDEC | access-date=2023-11-09 | archive-date=2024-09-17 | archive-url=https://web.archive.org/web/20240917213306/https://www.jedec.org/standards-documents/docs/module-444 | url-status=live }}</ref><ref>{{Cite web|url=http://archive.org/details/completeidiotsgu00fult|title=The complete idiot's guide to upgrading and repairing PCs|first=Jennifer|last=Fulton|date=November 9, 2000|publisher=Indianapolis, IN : Alpha Books|via=Internet Archive}}</ref> Before its introduction, many laptops would use proprietary<ref>{{Cite web|url=https://books.google.com/books?id=u2cfcECC1dwC&dq=%2260-pin%22+memory+card&pg=PP36|title=PC Magazine|last1=Jones|first1=Mitt|date=December 25, 1990|publisher=Ziff-Davis Publishing Company|via=Google Books|access-date=February 4, 2024|archive-date=September 17, 2024|archive-url=https://web.archive.org/web/20240917213428/https://books.google.com/books?id=u2cfcECC1dwC&dq=%2260-pin%22+memory+card&pg=PP36#v=onepage&q=%2260-pin%22%20memory%20card&f=false|url-status=live}}</ref> RAM modules which were expensive and hard to find.<ref name="auto"/><ref>{{cite book | url=https://books.google.com/books?id=O0FTac_k7CIC&dq=laptop+proprietary+sodimm&pg=PA36 | title=Peter Norton's New Inside the PC | isbn=9780672322891 | last1=Norton | first1=Peter | last2=Clark | first2=Scott H. | date=2002 | publisher=Sams }}</ref>
+<gallery>
+File:Notch position between DDR and DDR2.jpg|Notch positions on DDR (top) and DDR2 (bottom) DIMM modules.
+File:RAM DIMM 4GB by Kingston-top PNr°0306.jpg|upright=1.6|4 GB DDR VLP DIMM from [[Kingston Technology]]
+</gallery>
-SO-DIMMs are often used in computers that have limited space, which include [[laptop]]s, [[notebook computer]]s, small-footprint personal computers such as those based on [[Nano-ITX motherboard]]s, high-end upgradable office [[Computer printer|printers]], and [[networking hardware]] such as [[Router (computing)|routers]] and [[Network-attached storage|NAS]] devices.<ref>{{cite web |author=Synology Inc. |title=Synology RAM Module |url=https://www.synology.com/en-global/products/Synology_RAM_Module |work=synology.com |access-date=2022-03-23 |archive-date=2016-06-02 |archive-url=https://web.archive.org/web/20160602224830/https://www.synology.com/en-global/products/Synology_RAM_Module |url-status=live }}</ref> They are usually available with the same size data path and speed ratings of the regular DIMMs though normally with smaller capacities.
+=== Heights ===
+Several form factors are commonly used in DIMMs. Single Data Rate Synchronous DRAM (SDR SDRAM) DIMMs were primarily manufactured in {{convert|1.5|in|mm}} and {{convert|1.7|in|mm}} heights, with the nominal value being {{convert|30|mm|in}}. When [[rack unit|1U rackmount]] servers started becoming popular, these form factor registered DIMMs had to plug into angled DIMM sockets to fit in the {{convert|1.75|in|mm}} high box. To alleviate this issue, the next standards of DDR DIMMs were created with a "low profile" (LP) height of around {{convert|1.2|in|mm}}. These fit into vertical DIMM sockets for a 1U platform.
+With the advent of [[blade server]]s, angled slots have once again become common in order to accommodate LP form factor DIMMs in these space-constrained boxes. This led to the development of the Very Low Profile (VLP) form factor DIMM with a height of around {{convert|18|mm|in}}. These will fit vertically in [[Advanced Telecommunications Computing Architecture|ATCA]] systems.
+Very similar height levels are used for SO-DIMM, Mini-DIMM and Micro-DIMM.<ref>{{cite web |title=CST Inc,DDR5,DDR4,DDR3,DDR2,DDR,Nand,Nor,Flash,MCP,LPDDR,LPDDR2,LPDDR3,LPDDR4,LRDIMM, Memory Tester Automatic DIMM SODIMM Handler Company Provides Memory Solution |url=https://www.simmtester.com/News/PublicationArticle/168 |website=www.simmtester.com}}</ref>
+{|class=wikitable
+|+JEDEC standard heights for DIMMs<ref>{{cite web |title=MICROELECTRONIC OUTLINES (MO) |url=https://www.jedec.org/sites/default/files/MOINDEX.pdf |website=JEDEC}}</ref>
+|-
+! rowspan=2|Generation !! colspan=2|Full-height (1U) !! colspan=2|Very low profile (VLP) !! rowspan=2 |Notes
+|-
+! Nominal !! Maximum !! Nominal !! Maximum
+|-
+! DDR2<ref>JEDEC documents MO-256, MO-260, MO-274</ref>
+| {{convert|30.00|mm|in}} || {{convert|30.50|mm|in}}|| {{N/A}} || {{N/A}} ||
+|-
+! DDR3<ref>[http://www.jedec.org/sites/default/files/docs/MO-269J.pdf JEDEC MO-269J Whitepaper.], accessed Aug. 20, 2014.</ref>
+| {{convert|30.00|mm|in}} || {{convert|30.50|mm|in}}|| {{convert|18.75|mm|in}} || {{convert|18.90|mm|in}} ||
+|-
+! DDR4<ref>[http://www.jedec.org/sites/default/files/docs/MO-309E.pdf JEDEC MO-309E Whitepaper.], accessed Aug. 20, 2014.</ref>
+| {{convert|31.25|mm|in}} || {{convert|31.40|mm|in}}|| {{convert|18.75|mm|in}} || {{convert|18.90|mm|in}} ||
+|-
+! DDR5<ref>DIMM:[https://www.jedec.org/standards-documents/docs/mo-329j MO-329J]; SO-DIMM: [https://www.jedec.org/standards-documents/docs/mo-337b MO-337B].</ref>
+| {{convert|31.25|mm|in}} || {{convert|31.40|mm|in}}|| {{N/A}} || {{N/A}}
+|
+* For DIMMs, there is a new height called 2U DIMM at {{convert|56.90|mm|in}} nominal and {{convert|57.05|mm|in}} max.
+* DDR5 and LPDDR5 also use [[CAMM2]] units. These are mounted flush to the motherboard.
+|}
-== SDR 168-pin SDRAM ==
+Notes:
-[[File:Notch position between DDR and DDR2.jpg|thumb|right|upright=1.6|Notch positions on DDR (top) and DDR2 (bottom) DIMM modules.]]
+* Low profile (LP) is not a JEDEC standard.
+* The full JEDEC standards also regulate factors such as thickness.
+* SO-DIMMs for DDR4 and DDR5 maintain the traditional height of {{val|30.00|0.15}}&nbsp;mm; see JEDEC MO-310A and MO-337B. The height increase for "full height" DIMM does not apply to SO-DIMM.
+* It is common for higher-end consumer DDR4 DIMMs to exceed the JEDEC full height due to the use of an added [[heat sink]]. Some heat sinks add as little as {{convert|1|mm|in}} while others add up to {{convert|5|mm|in}}.
-On the bottom edge of 168-pin DIMMs there are two notches, and the location of each notch determines a particular feature of the module. The first notch is the DRAM key position, which represents RFU (reserved future use), [[Registered memory|registered]], and [[Unbuffered memory|unbuffered]] DIMM types (left, middle and right position, respectively). The second notch is the voltage key position, which represents 5.0&nbsp;V, 3.3&nbsp;V, and RFU DIMM types (order is the same as above).
+=== Similar connectors ===
-== DDR DIMMs ==
+As of Q2 2017, Asus has had a [[PCIe]] based "DIMM.2", which has a similar socket to DDR3 DIMMs and is used to put in a module to connect up to two [[M.2]] [[NVMe]] solid-state drives. However, it cannot use common DDR type ram and does not have much support from other than Asus.<ref>[https://www.techpowerup.com/229448/asus-dimm-2-is-an-m-2-riser-card ASUS DIMM.2 is a M.2 Riser Card.] {{Webarchive|url=https://web.archive.org/web/20200605022413/https://www.techpowerup.com/229448/asus-dimm-2-is-an-m-2-riser-card |date=2020-06-05 }}, accessed Jun. 4, 2020.</ref>
-[[File:16 GiB-DDR4-RAM-Riegel RAM019FIX Small Crop 90 PCNT.png|thumb|upright=1.6|16&nbsp;GiB DDR4-2666 1.2&nbsp;V [[UDIMM|Unbuffered DIMM (UDIMM)]].]]
-[[DDR SDRAM|DDR]], [[DDR2 SDRAM|DDR2]], [[DDR3]], [[DDR4]] and [[DDR5]] all have different pin counts and/or different notch positions, and none of them are [[forward compatible]] or [[backward compatible]]. DDR5 SDRAM is the most recent type of DDR memory and has been in use since 2020.
+== Components ==
+=== Organization ===
+Most DIMMs are built using "×4" ("by four") or "×8" ("by eight") memory chips with up to nine chips per side; "×4" and "×8" refer to the data width of the DRAM chips in bits. High-capacity DIMMs such as 256&nbsp;GB DIMMs can have up to 19 chips per side.
-== SPD EEPROM ==
+In the case of "×4" registered DIMMs, the data width per side is 36 bits; therefore, the [[memory controller]] (which requires 72 bits) needs to address both sides at the same time to read or write the data it needs. In this case, the two-sided module is single-ranked. For "×8" registered DIMMs, each side is 72 bits wide, so the memory controller only addresses one side at a time (the two-sided module is dual-ranked).
-A DIMM's capacity and other operational parameters may be identified with [[serial presence detect]] (SPD), an additional chip which contains information about the module type and timing for the memory controller to be configured correctly. The SPD [[EEPROM]] connects to the [[System Management Bus]] and may also contain thermal sensors (''TS-on-DIMM'').<ref>{{Cite web |url=http://www.tempsensornews.com/generic-temp-sensors/temperature-sensor-in-dimm-memory-modules/ |title=Temperature Sensor in DIMM memory modules |access-date=2013-03-17 |archive-date=2016-04-01 |archive-url=https://web.archive.org/web/20160401094930/http://www.tempsensornews.com/generic-temp-sensors/temperature-sensor-in-dimm-memory-modules/ |url-status=usurped }}</ref>
-== Error correction ==
+The above example applies to ECC memory that stores 72 bits instead of the more common 64. There would also be one extra chip per group of eight, which is not counted.
-[[ECC memory|ECC]] DIMMs are those that have extra data bits which can be used by the system memory controller to detect and correct errors. There are numerous ECC schemes, but perhaps the most common is Single Error Correct, Double Error Detect ([[SECDED]]) which uses an extra byte per 64-bit word. ECC modules usually carry a multiple of 9 instead of a multiple of 8 chips.
-== Ranking ==
+==== Ranking ====
 {{main|Memory rank}}
-Sometimes memory modules are designed with two or more independent sets of DRAM chips connected to the same address and data buses; each such set is called a '''rank'''. Ranks that share the same slot, only one rank may be accessed at any given time; it is specified by activating the corresponding rank's chip select (CS) signal. The other ranks on the module are deactivated for the duration of the operation by having their corresponding CS signals deactivated. DIMMs are currently being commonly manufactured with up to four ranks per module. Consumer DIMM vendors have recently begun to distinguish between single and dual ranked DIMMs.
+Sometimes, memory modules are designed with two or more independent sets of DRAM chips connected to the same address and data buses; each such set is called a ''rank''. Of the ranks that share the same memory slot, i.e. on the same module, only one rank may be accessed at any given time. The rank to be accessed is specified by activating its chip select (CS) signal, while the other ranks on the same module are deactivated for the duration of the operation by having their corresponding CS signals deactivated.
+After a memory word is fetched, the memory is typically inaccessible for an extended period of time while the sense amplifiers are charged for access of the next cell. These amplifiers typically have 3 cycles of idle time for recharging between accesses. By interleaving the memory (e.g. cells 0, 4, 8, ... are stored in one rank, cells 1, 5, 9, ... in another rank, and so on), sequential memory accesses can be performed more rapidly by alternating which rank is active, thus overlapping the active memory access with recharge time for the inactive ranks.
-After a memory word is fetched, the memory is typically inaccessible for an extended period of time while the sense amplifiers are charged for access of the next cell. By interleaving the memory (e.g. cells 0, 4, 8, etc. are stored together in one rank), sequential memory accesses can be performed more rapidly because sense amplifiers have 3 cycles of idle time for recharging, between accesses.
+{{As of|2025}}, DIMMs are commonly manufactured with one, two, or four ranks per module. Consumer DIMM vendors have began to distinguish between single- and dual-ranked DIMMs since around 2020.
-DIMMs are often referred to as "single-sided" or "[[Double-sided RAM|double-sided]]" to describe whether the DRAM chips are located on one or both sides of the module's [[printed circuit board]] (PCB). However, these terms may cause confusion, as the physical layout of the chips does not necessarily relate to how they are logically organized or accessed.
+DIMMs are often referred to as "single-sided" or "[[Double-sided RAM|double-sided]]" to describe whether the DRAM chips are located on one or both sides of the module's [[printed circuit board]] (PCB). However, these terms may cause confusion, as the physical layout of the chips does not necessarily relate to how they are logically organized or accessed. Indeed, quad-ranked DIMMs exist.
 [[JEDEC]] decided that the terms "dual-sided", "double-sided", or "dual-banked" were not correct when applied to [[registered DIMM]]s (RDIMMs).
-== Organization ==
+Multiplexed Rank DIMM (MRDIMM) allow data from multiple ranks to be transmitted on the same channel. It was announced for DDR5 in July 2024 and is expected to be backwards compatible with DDR5 RDIMM.<ref>{{cite press release
-Most DIMMs are built using "×4" ("by four") or "×8" ("by eight") memory chips with up to nine chips per side; "×4" and "×8" refer to the data width of the DRAM chips in bits. High-capacity DIMMs such as 256&nbsp;GB DIMMs can have up to 19 chips per side.
+ |title=JEDEC Unveils Plans for DDR5 MRDIMM and LPDDR6 CAMM Standards to Propel High-Performance Computing and AI
+ |date=22 July 2024
+ |publisher=[[JEDEC]]
+ |url=https://www.jedec.org/news/pressreleases/jedec-unveils-plans-ddr5-mrdimm-and-lpddr6-camm-standards-propel-high-performance
+}}</ref>
-In the case of "×4" registered DIMMs, the data width per side is 36 bits; therefore, the [[memory controller]] (which requires 72 bits) needs to address both sides at the same time to read or write the data it needs. In this case, the two-sided module is single-ranked. For "×8" registered DIMMs, each side is 72 bits wide, so the memory controller only addresses one side at a time (the two-sided module is dual-ranked).
+=== SPD EEPROM ===
+A DIMM's capacity and other operational parameters may be identified with [[serial presence detect]] (SPD), an additional chip which contains information about the module type and timing for the memory controller to be configured correctly. The SPD [[EEPROM]] connects to the [[System Management Bus]] and may also contain thermal sensors (''TS-on-DIMM'').<ref>{{Cite web |url=http://www.tempsensornews.com/generic-temp-sensors/temperature-sensor-in-dimm-memory-modules/ |title=Temperature Sensor in DIMM memory modules |access-date=2013-03-17 |archive-date=2016-04-01 |archive-url=https://web.archive.org/web/20160401094930/http://www.tempsensornews.com/generic-temp-sensors/temperature-sensor-in-dimm-memory-modules/ |url-status=usurped }}</ref>
-The above example applies to ECC memory that stores 72 bits instead of the more common 64. There would also be one extra chip per group of eight, which is not counted.
+== Features ==
-== Speeds ==
+=== Speeds ===
 For various technologies, there are certain bus and device clock frequencies that are standardized; there is also a decided nomenclature for each of these speeds for each type.
 DIMMs based on Single Data Rate (SDR) DRAM have the same bus frequency for data, address and control lines. DIMMs based on [[Double Data Rate]] (DDR) DRAM have data but not the strobe at double the rate of the clock; this is achieved by clocking on both the rising and falling edge of the data strobes. Power consumption and voltage gradually became lower with each generation of DDR-based DIMMs.
-Another influence is Column Access Strobe (CAS) latency, or CL, which affects memory access speed. This is the delay time between the READ command and the moment data is available. See main article [[CAS latency|CAS/CL]].
+Another influence is Column Access Strobe (CAS) latency, or CL, which affects memory access speed. This is the delay time between the READ command and the moment data is available. See main article [[CAS latency|CAS/CL]] and [[memory timing]].
 {{Col-float|width=50em}}
@@ Line 283: / Line 344: @@
 {{Col-float-end}}
-== Form factors ==
+=== Error correction ===
-[[File:Laptop_SODIMM_DDR_Memory_Comparison_V2.svg|right|thumb|A comparison between 200-pin DDR and DDR2 SDRAM SO-DIMMs, and a 204-pin DDR3 SO-DIMM module.<ref name="custhelp">{{cite web
+[[ECC memory|ECC]] DIMMs are those that have extra data bits which can be used by the system memory controller to detect and correct errors. There are numerous ECC schemes, but perhaps the most common is Single Error Correct, Double Error Detect ([[SECDED]]) which uses an extra byte per 64-bit word. ECC modules usually carry a multiple of 9 instead of a multiple of 8 chips as a result.
- | url = http://acer.custhelp.com/app/answers/detail/a_id/2178/~/are-ddr,-ddr2-and-ddr3-so-dimm-memory-modules-interchangeable%3F
- | title = Are DDR, DDR2 and DDR3 SO-DIMM memory modules interchangeable?
- | access-date = 2015-06-26
- | website = acer.custhelp.com
- }}{{Dead link|date=September 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>]]
-Several form factors are commonly used in DIMMs. Single Data Rate Synchronous DRAM (SDR SDRAM) DIMMs were primarily manufactured in {{convert|1.5|in|mm}} and {{convert|1.7|in|mm}} heights. When [[rack unit|1U rackmount]] servers started becoming popular, these form factor registered DIMMs had to plug into angled DIMM sockets to fit in the {{convert|1.75|in|mm}} high box. To alleviate this issue, the next standards of DDR DIMMs were created with a "low profile" (LP) height of around {{convert|1.2|in|mm}}. These fit into vertical DIMM sockets for a 1U platform.
-With the advent of [[blade server]]s, angled slots have once again become common in order to accommodate LP form factor DIMMs in these space-constrained boxes. This led to the development of the Very Low Profile (VLP) form factor DIMM with a height of around {{convert|0.72|in|mm}}. The DDR3 JEDEC standard for VLP DIMM height is around {{convert|0.740|in|mm}}. These will fit vertically in [[Advanced Telecommunications Computing Architecture|ATCA]] systems.
-Full-height 240-pin DDR2 and DDR3 DIMMs are all specified at a height of around {{convert|1.18|in|mm}} by standards set by JEDEC. These form factors include 240-pin DIMM, SO-DIMM, Mini-DIMM and Micro-DIMM.<ref>[http://www.jedec.org/sites/default/files/docs/MO-269J.pdf JEDEC MO-269J Whitepaper.], accessed Aug. 20, 2014.</ref>
-Full-height 288-pin DDR4 DIMMs are slightly taller than their DDR3 counterparts at {{convert|1.23|in|mm}}. Similarly, VLP DDR4 DIMMs are also marginally taller than their DDR3 equivalent at nearly {{convert|0.74|in|mm}}.<ref>[http://www.jedec.org/sites/default/files/docs/MO-309E.pdf JEDEC MO-309E Whitepaper.], accessed Aug. 20, 2014.</ref>
-As of Q2 2017, Asus has had a [[PCI-E]] based "DIMM.2", which has a similar socket to DDR3 DIMMs and is used to put in a module to connect up to two [[M.2]] [[NVMe]] solid-state drives. However, it cannot use common DDR type ram and does not have much support other than Asus.<ref>[https://www.techpowerup.com/229448/asus-dimm-2-is-an-m-2-riser-card ASUS DIMM.2 is a M.2 Riser Card.] {{Webarchive|url=https://web.archive.org/web/20200605022413/https://www.techpowerup.com/229448/asus-dimm-2-is-an-m-2-riser-card |date=2020-06-05 }}, accessed Jun. 4, 2020.</ref>
+=== Register/buffer ===
+It is electrically demanding for a memory controller to drive many DIMMs. [[Registered DIMM]]s add a [[hardware register]] to the clock, address, and command lines so that the signals are refreshed on the DIMM, allowing a reduced load on the memory controller. Variants include LRDIMM with all lines buffered and CUDIMM/CSODIMM with only the clock signal buffered. The register feature often occurs with ECC, but they do not actually depend on each other and can occur independently.
-Regular DIMMs are generally 133.35&nbsp;mm in length, while SO-DIMMs are generally 67.6&nbsp;mm in length.<ref name=":0">{{cite web |url=https://www.simmtester.com/News/PublicationArticle/168 |date=2009-10-06 |accessdate=2021-05-13 |title=Common DIMM Memory Form Factor |archive-date=2021-05-13 |archive-url=https://web.archive.org/web/20210513093518/https://www.simmtester.com/News/PublicationArticle/168 |url-status=live }}</ref>
+{{clear}}
 == See also ==
@@ Line 327: / Line 377: @@
 * [http://www.oempcworld.com/support/How_to_Install_PC_Memory.htm How to Install PC Memory guides]
 * [http://www.supertalent.com/datasheets/VLP_WHITEPAPER.pdf Very Low Profile (VLP) DDR2 Whitepaper (PDF)]
-* [https://reviewpanther.com/is-4gb-ram-good-for-a-laptop/ Is 4GB RAM Good For a Laptop?]
+* [https://reviewpanther.com/is-4gb-ram-good-for-a-laptop/ Is 4GB RAM Good For a Laptop?] {{Webarchive|url=https://web.archive.org/web/20221003075153/https://reviewpanther.com/is-4gb-ram-good-for-a-laptop/ |date=2022-10-03 }}
 {{DRAM}}
 [[Category:Computer memory form factor]]

DIMM: Difference between revisions

Latest revision as of 05:42, 16 November 2025

Contents

History

Form factors

Widths

SO-DIMM

Connector

Heights

Similar connectors

Components

Organization

Ranking

SPD EEPROM

Features

Speeds

Error correction

Register/buffer

See also

References

External links

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DIMM: Difference between revisions

Latest revision as of 05:42, 16 November 2025

History

Form factors

Widths

SO-DIMM

Connector

Heights

Similar connectors

Components

Organization

Ranking

SPD EEPROM

Features

Speeds

Error correction

Register/buffer

See also

References

External links

Navigation menu

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