A
DIMM, or
dual in-line memory module, comprises a series of
dynamic random access memoryDynamic random access memory is a type of random access memory that stores each bit of data in a separate capacitor within an integrated circuit. Since real capacitors leak charge, the information eventually fades unless the capacitor charge is refreshed periodically...
integrated circuitIn electronics, an integrated circuit is a miniaturized electronic circuit that has been manufactured in the surface of a thin substrate of semiconductor material...
s. These modules are mounted on a
printed circuit boardA printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, or traces, etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board or etched wiring board...
and designed for use in
personal computerA personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end user, with no intervening computer operator...
s,
workstationA 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 and
serverA server is an application running on a computer that delivers a service. For example, a web server will deliver web pages when requested by a browser . The way a server and a client dialogs is called a protocol...
s. DIMMs began to replace
SIMMA SIMM, or single in-line memory module, is a type of memory module containing random access memory used in computers from the early 1980s to the late 1990s. It differs from a dual in-line memory module , the most predominant form of memory module today, in that the contacts on a SIMM are redundant...
s (single in-line memory modules) as the predominant type of memory module as Intel's
PentiumThe original Pentium processor was a 32-bit microprocessor produced by Intel. The first superscalar x86 architecture processor, it was introduced on March 22, 1993. Its microarchitecture was a direct extension of the 80486 architecture with dual integer pipelines, a faster FPU, wider data bus, and...
processors began to gain market share.
The main difference between SIMMs and DIMMs is that DIMMs have separate electrical contacts on each side of the module, while the contacts on SIMMs on both sides are redundant.
A
DIMM, or
dual in-line memory module, comprises a series of
dynamic random access memoryDynamic random access memory is a type of random access memory that stores each bit of data in a separate capacitor within an integrated circuit. Since real capacitors leak charge, the information eventually fades unless the capacitor charge is refreshed periodically...
integrated circuitIn electronics, an integrated circuit is a miniaturized electronic circuit that has been manufactured in the surface of a thin substrate of semiconductor material...
s. These modules are mounted on a
printed circuit boardA printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, or traces, etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board or etched wiring board...
and designed for use in
personal computerA personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end user, with no intervening computer operator...
s,
workstationA 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 and
serverA server is an application running on a computer that delivers a service. For example, a web server will deliver web pages when requested by a browser . The way a server and a client dialogs is called a protocol...
s. DIMMs began to replace
SIMMA SIMM, or single in-line memory module, is a type of memory module containing random access memory used in computers from the early 1980s to the late 1990s. It differs from a dual in-line memory module , the most predominant form of memory module today, in that the contacts on a SIMM are redundant...
s (single in-line memory modules) as the predominant type of memory module as Intel's
PentiumThe original Pentium processor was a 32-bit microprocessor produced by Intel. The first superscalar x86 architecture processor, it was introduced on March 22, 1993. Its microarchitecture was a direct extension of the 80486 architecture with dual integer pipelines, a faster FPU, wider data bus, and...
processors began to gain market share.
The main difference between SIMMs and DIMMs is that DIMMs have separate electrical contacts on each side of the module, while the contacts on SIMMs on both sides are redundant. Another difference is that standard SIMMs have a 32-bit data path, while standard DIMMs have a 64-bit data path. Since Intel's Pentium has (as do several other processors) a 64-bit bus width, it requires SIMMs installed in matched pairs in order to complete the data bus. The processor would then access the two SIMMs simultaneously. DIMMs were introduced to eliminate this practice.
The most common types of DIMMs are:
- 72-pin SO-DIMM
A SO-DIMM, or small outline dual in-line memory module, is a type of computer memory built using integrated circuits.SO-DIMMs are a smaller alternative to a DIMM, being roughly half the size of regular DIMMs...
(not the same as a 72-pin SIMM), used for FPM DRAM and EDO DRAM
- 100-pin DIMM, used for printer SDRAM
Synchronous dynamic random access memory is dynamic random access memory that has a synchronous interface. Traditionally, dynamic random access memory has an asynchronous interface which means that it responds as quickly as possible to changes in control inputs...
- 144-pin SO-DIMM, used for SDR SDRAM
- 168-pin DIMM, used for SDR SDRAM (less frequently for FPM/EDO DRAM in workstations/servers)
- 172-pin MicroDIMM, used for DDR
Double data rate synchronous dynamic random access memory is a class of memory integrated circuits used in computers. It achieves nearly twice the bandwidth of the preceding single data rate SDRAM by double pumping without increasing the clock frequency.With data being transferred 64 bits at...
SDRAM
- 184-pin DIMM, used for DDR SDRAM
- 200-pin SO-DIMM, used for DDR SDRAM and DDR2
DDR2 SDRAM is a double data rate synchronous dynamic random access memory interface. It supersedes the original DDR SDRAM specification and the two are not compatible...
SDRAM
- 204-pin SO-DIMM, used for DDR3
In electronic engineering, DDR3 SDRAM or double-data-rate three synchronous dynamic random access memory is a random access memory interface technology used for high bandwidth storage of the working data of a computer or other digital electronic devices...
SDRAM
- 214-pin MicroDIMM, used for DDR2 SDRAM
- 240-pin DIMM, used for DDR2 SDRAM, DDR3
In electronic engineering, DDR3 SDRAM or double-data-rate three synchronous dynamic random access memory is a random access memory interface technology used for high bandwidth storage of the working data of a computer or other digital electronic devices...
SDRAM and FB-DIMMFully Buffered DIMM is a memory technology which can be used to increase reliability, speed and density of memory systems. Conventionally, data lines from the memory controller have to be connected to data lines in every DRAM module. As memory width, as well as access speed, increases, the signal...
DRAM
Key positions
The various types of memory have different key positions that allow for fool proof installation and disallow incompatible memory types to be installed.
168-pin SDRAM
On the bottom edge of 168-pin DIMMs there are 2 notches, and the location of each notch determines a particular feature of the module.
- The first notch is DRAM key position. It represents RFU (reserved future use), registered
Registered memory modules have a register between the DRAM modules and the system's memory controller. They place less electrical load on the memory controller and allow single systems to remain stable with more memory modules than they would have otherwise...
, and unbuffered (in that order from left to middle to right position).
- The second notch is voltage key position. It represents 5.0V, 3.3V, and Reserved (order as above).
- The upper DIMM in the photo is an unbuffered 3.3V 168-pin DIMM.
SPD EPROM
A DIMM's capacity and timing parameters may be identified with
Serial Presence DetectSerial presence detect refers to a standardized way to automatically access information about a computer memory module. Earlier 72-pin SIMMs included 5 pins which provided 5 bits of parallel presence detect data, but the 168-pin DIMM standard changed to a serial presence detect to encode much...
(SPD), an additional chip which contains information about the module type and timing for the memory controller to be configured correctly.
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 (
SECDEDIn telecommunication, a Hamming code is a linear error-correcting code named after its inventor, Richard Hamming. Hamming codes can detect up to two simultaneous bit errors, and correct single-bit errors; thus, reliable communication is possible when the Hamming distance between the transmitted and...
) 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
The number of ranks on any DIMM is the number of independent sets of DRAMs that can be accessed for the full data bit-width of the DIMM ie 64 bits. The ranks cannot be accessed simultaneously as they share the same data path. The physical layout of the DRAM chips on the DIMM itself does not necessarily relate to the number of ranks.
DIMMs are often referred to as "single-sided" or "
double-sidedDouble-sided RAM is a type of random-access memory which has its chips divided into two sides , only one of which can be seen at a time by the computer. Initially, these were created by essentially attaching two single-sided SIMM cards to the same PCB, but more modern chips use different wiring...
" in reference to the location of the memory devices or "chips" being on only one or both sides of the DIMM printed-circuit board (PCB). These terms may cause confusion as they do not necessarily relate to how the DIMMs are logically organized or accessed.
For example, on a single-rank DIMM that has 64 data bits of I/O pins, there is only one set of DRAMs that are turned on to drive a read or receive a write on all 64 bits. In most electronic systems, memory controllers are designed to access the full data bus width of the memory module at the same time.
On a 64-bit (non-ECC) DIMM made with two ranks, there would be two sets of DRAM that could be accessed at different times. Only one of the ranks can be accessed at a time, since the DRAM data bits are tied together for two loads on the DIMM (Wired OR). Ranks are accessed through chip selects (CS). Thus for a two rank module, the two DRAMs with data bits tied together may be accessed by a CS per DRAM (e.g. CS0 goes to one DRAM chip and CS1 goes to the other). 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.
JEDECJEDEC Solid State Technology Association, formerly known as Joint Electron Device Engineering Council , is the semiconductor engineering standardization body of the Electronic Industries Alliance , a trade association that represents all areas of the electronics industry in the United States...
decided that the terms "dual-sided," "double-sided," or "dual-banked" were not correct when applied to registered DIMMs.
Organization
Most DIMMs are built using "x4" (by 4) memory chips or "x8" (by 8) memory chips with 9 chips per side. "x4" or "x8" refer to the data width of the DRAM chips in bits.
In the case of the "x4"-registered DIMMs, the data width per side is 36 bits; therefore, the
memory controllerThe memory controller is a digital circuit which manages the flow of data going to and from the main memory. It can be a separate chip or integrated into another chip, such as on the die of a microprocessor....
(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 "x8"-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).
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.
SDR SDRAM DIMMs
- These first synchronous registered DRAM DIMMs had the same bus frequency for data, address and control lines.
- PC66 = 66 MHz
- PC100 = 100 MHz
- PC133 = 133 MHz
DDR SDRAMDouble data rate synchronous dynamic random access memory is a class of memory integrated circuits used in computers. It achieves nearly twice the bandwidth of the preceding single data rate SDRAM by double pumping without increasing the clock frequency.With data being transferred 64 bits at...
(DDR1) SDRAM DIMMs
- 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.
- PC1600 = 200 MHz data & strobe / 100 MHz clock for address and control
- PC2100 = 266 MHz data & strobe / 133 MHz clock for address and control
- PC2700 = 333 MHz data & strobe / 166 MHz clock for address and control
- PC3200 = 400 MHz data & strobe / 200 MHz clock for address and control
DDR2 SDRAMDDR2 SDRAM is a double data rate synchronous dynamic random access memory interface. It supersedes the original DDR SDRAM specification and the two are not compatible...
SDRAM DIMMs
- DIMMs based on Double Data Rate 2 (DDR2) DRAM also have data and data strobe frequencies at double the rate of the clock. This is achieved by clocking on both the rising and falling edge of the data strobes. The power consumption and voltage of DDR2 is significantly lower than DDR(1) at the same speed.
- PC2-3200 = 400 MHz data & strobe / 200 MHz clock for address and control
- PC2-4200 = 533 MHz data & strobe / 266 MHz clock for address and control
- PC2-5300 = 667 MHz data & strobe / 333 MHz clock for address and control
- PC2-6400 = 800 MHz data & strobe / 400 MHz clock for address and control
- PC2-8000 = 1000 MHz data & strobe / 500 MHz clock for address and control
- PC2-8500 = 1066 MHz data & strobe / 533 MHz clock for address and control
- PC2-9600 = 1200 MHz data & strobe / 600 MHz clock for address and control
DDR3 SDRAMIn electronic engineering, DDR3 SDRAM or double-data-rate three synchronous dynamic random access memory is a random access memory interface technology used for high bandwidth storage of the working data of a computer or other digital electronic devices...
SDRAM DIMMs
- DIMMs based on Double Data Rate 3(DDR3) DRAM have data and strobe frequencies at double the rate of the clock. This is achieved by clocking on both the rising and falling edge of the data strobes. The power consumption and voltage of DDR3 is lower than DDR2 of the same speed.
- PC3-6400 = 800 MHz data & strobe / 400 MHz clock for address and control
- PC3-8500 = 1066 MHz data & strobe / 533 MHz clock for address and control
- PC3-10600 = 1333 MHz data & strobe / 667 MHz clock for address and control
- PC3-12800 = 1600 MHz data & strobe / 800 MHz clock for address and control
- PC3 16000 = 2000 MHz data & strobe / 1000 MHz clock for address and control
Form factors
Several form factors are commonly used in DIMMs. Single Data Rate (SDR) SDRAM DIMMs commonly came in two main sizes: 1.7-inch and 1.5-inch. When 1U rackmount servers started becoming popular, these form factor Registered DIMMs had to plug into angled DIMM sockets to fit in the 1.75" high box. To alleviate this issue, the next standards of DDR DIMMs were created with a "Low Profile" (LP) height of ~1.2". These fit into vertical DIMM sockets for a 1U platform. With the advent of blade servers, the LP form factor DIMMs have once again been often angled to fit in these space-constrained boxes. This led to the development of the Very Low Profile (VLP) form factor DIMM with a height of ~.72" (18.3 mm). The DDR3 JEDEC standard for VLP DIMM height is 18.75mm. These will fit vertically in ATCA systems. Other DIMM form factors include the SO-DIMM, the Mini-DIMM and the VLP Mini-DIMM.
See also
- Dual in-line package
In 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. The pins are all parallel, point downward, and extend past the bottom plane of the package at least enough...
(DIP)
- Rambus in-line memory module
Direct Rambus DRAM or DRDRAM is a type of synchronous dynamic RAM, designed by the Rambus Corporation.- Personal computers :The first PC motherboards with support for RDRAM debuted in 1999...
(RIMM)
- Single in-line memory module (SIMM)
- Single in-line package
A single in-line package is an electronic device package which has one row of connecting pins. It is not as popular as the dual in-line package, but has been used for packaging RAM chips and multiple resistors with a common pin.-See also:...
(SIP)
- SO-DIMM
A SO-DIMM, or small outline dual in-line memory module, is a type of computer memory built using integrated circuits.SO-DIMMs are a smaller alternative to a DIMM, being roughly half the size of regular DIMMs...
- Zig-zag in-line package
The zig-zag in-line package or ZIP was a short-lived packaging technology for integrated circuits, particularly dynamic RAM chips. It was intended as a replacement for dual in-line packaging . A ZIP is an integrated circuit encapsulated in a slab of plastic, measuring about 3 mm x 30 mm x 10 mm. ...
(ZIP)
External links