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 only one. Also, each module has eight RAM chips, but the lower one has an unoccupied space for the ninth chip.

Three SDRAM DIMM slots on a computer motherboard

The 2 GB DIMM in slot 1 and the lower 2 GB of the DIMM in slot 2 operate together in dual-channel mode. The remaining (upper) 2 GB of the DIMM in slot 2 operates in single-channel mode. Upvote 2 downvote 0. I have a Flex2 15D and was trying to upgrade the memory - System shows 2 DIMM slots and that it is upgradable to 16G - It came with 4GB Removed the back per hardware maintenance manual instructions but I can only find 1 DIMM slot. I was able to put in 8GB instead of 4 - but would like to find the. 2008 Transcend has announced the availability of 2GB DDR2-800 fully-buffered DIMM (FB-DIMM)) designed specifically for which memory slots 2 dimm Apples high-end Mac Pro systems. The Mac Pro is based on Quad-Core Intel Xeon 5400 platform, and has a total of eight. Slotty Vegas reserves the right to suspend a cash-out request pending verification of User’s identity, age and location of memory slots 2 dimm the bearer of memory slots 2 dimm the account. The subscriber implicitly gives his authorization to the processing of any personal memory slots 2 dimm data in compliance with the privacy laws in force in Malta. Jan 09, 2014 You should install 2 of the same sticks as a matching pair on the same color slots and then another 2 that are the same in the remaining two slots. Ideally you want to have all memory be identical in a system or else you will end up with some memory being potentially downclocked (or voltage/multiplier) to the lowest common denominator.

A DIMM or dual in-line memory module comprises a series of dynamic random-access memoryintegrated circuits. These modules are mounted on a printed circuit board and designed for use in personal computers, workstations and servers. DIMMs began to replace SIMMs (single in-line memory modules) as the predominant type of memory module as IntelP5-based Pentium processors began to gain market share.

While the contacts on SIMMs on both sides are redundant, DIMMs have separate electrical contacts on each side of the module. 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, many processors have a 64-bit bus width, requiring 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.

Variants[edit]

Variants of DIMM slots support DDR, DDR2, DDR3 and DDR4 RAM.

Common types of DIMMs include the following:

SDRAM	SDR SDRAM	DDR SDRAM	DDR2 SDRAM	DDR3 SDRAM	DDR4 SDRAM	FPM DRAM и EDO DRAM	FB-DIMM DRAM
DIMM	100-pin	168-pin	184-pin	240-pin^[a]		288-pin	168-pin	240-pin
SO-DIMM	N/A	144-pin	200-pin^[a]		204-pin	260-pin	72-pin/144-pin	N/A
MicroDIMM	N/A	144-pin	172-pin	214-pin	N/A		N/A

70 to 200 pins

72-pin SO-DIMM (not the same as a 72-pin SIMM), used for FPM DRAM and EDO DRAM
100-pin DIMM, used for printer SDRAM
144-pin SO-DIMM, used for SDR SDRAM (less frequently for DDR2 SDRAM)
168-pin DIMM, used for SDR SDRAM (less frequently for FPM/EDO DRAM in workstations/servers, may be 3.3 or 5 V)
172-pin MicroDIMM, used for DDR SDRAM
184-pin DIMM, used for DDR SDRAM
200-pin SO-DIMM, used for DDR SDRAM and DDR2 SDRAM
200-pin DIMM, used for FPM/EDO DRAM in some Sun workstations and servers.

201 to 300 pins

204-pin SO-DIMM, used for DDR3 SDRAM
214-pin MicroDIMM, used for DDR2 SDRAM
240-pin DIMM, used for DDR2 SDRAM, DDR3 SDRAM and FB-DIMM DRAM
244-pin MiniDIMM, used for DDR2 SDRAM
260-pin SO-DIMM, used for DDR4 SDRAM
260-pin SO-DIMM, with different notch position than on DDR4 SO-DIMMs, used for UniDIMMs that can carry either DDR3 or DDR4 SDRAM
278-pin DIMM, used for HP high density SDRAM.
288-pin DIMM, used for DDR4 SDRAM

168-pin SDRAM[edit]

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

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, and unbuffered DIMM types (left, middle and right position, respectively). The second notch is the voltage key position, which represents 5.0 V, 3.3 V, and RFU DIMM types (order is the same as above).

DDR DIMMs[edit]

8 GB DDR4-2133 ECC 1.2 V RDIMMs

DDR, DDR2, DDR3 and DDR4 all have different pin counts, and different notch positions. As of August, 2014, DDR4 SDRAM is a modern emerging type of dynamic random access memory (DRAM) with a high-bandwidth ('double data rate') interface, and has been in use since 2013. It is the higher-speed successor to DDR, DDR2 and DDR3. DDR4 SDRAM is neither forward nor backward compatible with any earlier type of random access memory (RAM) because of different signalling voltages, timings, as well as other differing factors between the technologies and their implementation.

SPD EEPROM[edit]

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).^[1]

Error correction[edit]

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[edit]

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.

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.

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.

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

Organization[edit]

Most DIMMs are built using '×4' ('by four') or '×8' ('by eight') memory chips with nine chips per side; '×4' and '×8' refer to the data width of the DRAM chips in bits.

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