A
DIMM
DIMM or dual in-line memory module comprises a series of dynamic
random-access memory integrated 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 Intel
P5-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.
Contents
1 Variants
2 168-pin SDRAM
3 DDR DIMMs
4 SPD EEPROM
5 Error correction
6 Ranking
7 Organization
8 Speeds
9 Form factors
10 See also
11 References
12 External links
Variants[edit]
Variants of
DIMM
DIMM slots support DDR, DDR2, DDR3 and DDR4 RAM.
Common types of DIMMs include the following:
70 to 200 pins
72-pin
SO-DIMM
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
SDRAM (less frequently for DDR2 SDRAM)
168-pin DIMM, used for SDR
SDRAM
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
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
SDRAM and FB-
DIMM
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
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
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
DIMM types (order is the same as above).
DDR DIMMs[edit]
Two 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
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
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
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]
Main article: 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. Since all ranks share the same buses, only
one rank may be accessed at any given time; it is specified by
activating the corresponding rank's chip select (CS) signal. All other
ranks 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
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.
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
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.
Speeds[edit]
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.
SDR
SDRAM
SDRAM DIMMs
Chip
Module
Effective Clock
Voltage
SDR-66
PC-66
66 MHz
3.3 V
SDR-100
PC-100
100 MHz
3.3 V
SDR-133
PC-133
133 MHz
3.3 V
DDR
SDRAM
SDRAM (DDR1) DIMMs
Chip
Module
Memory Clock
I/O Bus Clock
Transfer rate
Voltage
DDR-200
PC-1600
100 MHz
100 MHz
200 MT/s
2.5 V
DDR-266
PC-2100
133 MHz
133 MHz
266 MT/s
2.5 V
DDR-333
PC-2700
166 MHz
166 MHz
333 MT/s
2.5 V
DDR-400
PC-3200
200 MHz
200 MHz
400 MT/s
2.5 V
DDR2
SDRAM
SDRAM DIMMs
Chip
Module
Memory Clock
I/O Bus Clock
Transfer rate
Voltage
DDR2-400
PC2-3200
200 MHz
200 MHz
400 MT/s
1.8 V
DDR2-533
PC2-4200
266 MHz
266 MHz
533 MT/s
1.8 V
DDR2-667
PC2-5300
333 MHz
333 MHz
667 MT/s
1.8 V
DDR2-800
PC2-6400
400 MHz
400 MHz
800 MT/s
1.8 V
DDR2-1066
PC2-8500
533 MHz
533 MHz
1066 MT/s
1.8 V
DDR3
SDRAM
SDRAM DIMMs
Chip
Module
Memory Clock
I/O Bus Clock
Transfer rate
Voltage
DDR3-800
PC3-6400
400 MHz
400 MHz
800 MT/s
1.5 V
DDR3-1066
PC3-8500
533 MHz
533 MHz
1066 MT/s
1.5 V
DDR3-1333
PC3-10600
667 MHz
667 MHz
1333 MT/s
1.5 V
DDR3-1600
PC3-12800
800 MHz
800 MHz
1600 MT/s
1.5 V
DDR3-1866
PC3-14900
933 MHz
933 MHz
1866 MT/s
1.5 V
DDR3-2133
PC3-17000
1066 MHz
1066 MHz
2133 MT/s
1.5 V
DDR3-2400
PC3-19200
1200 MHz
1200 MHz
2400 MT/s
1.5 V
DDR4
SDRAM
SDRAM DIMMs
Chip
Module
Memory Clock
I/O Bus Clock
Transfer rate
Voltage
DDR4-1600
PC4-12800
800 MHz
800 MHz
1600 MT/s
1.2 V
DDR4-1866
PC4-14900
933 MHz
933 MHz
1866 MT/s
1.2 V
DDR4-2133
PC4-17000
1066 MHz
1066 MHz
2133 MT/s
1.2 V
DDR4-2400
PC4-19200
1200 MHz
1200 MHz
2400 MT/s
1.2 V
DDR4-2666
PC4-21300
1333 MHz
1333 MHz
2666 MT/s
1.2 V
DDR4-3200
PC4-25600
1600 MHz
1600 MHz
3200 MT/s
1.2 V
Form factors[edit]
Several form factors are commonly used in DIMMs. Single Data Rate
Synchronous DRAM (SDR SDRAM) DIMMs were primarily manufactured in 1.5
inches (38 mm) and 1.7 inches (43 mm) heights. When 1U
rackmount servers started becoming popular, these form factor
registered DIMMs had to plug into angled
DIMM
DIMM sockets to fit in the
1.75 inches (44 mm) high box. To alleviate this issue, the next
standards of DDR DIMMs were created with a "low profile" (LP) height
of around 1.2 inches (30 mm). 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
DIMM with a height of around 0.72 inches
(18 mm). The DDR3
JEDEC
JEDEC standard for VLP
DIMM
DIMM height is around
0.740 inches (18.8 mm). These will fit vertically in ATCA
systems.
Full-height 240-pin DDR2 and DDR3 DIMMs are all specified at a height
of around 1.18 inches (30 mm) by standards set by JEDEC. These
form factors include 240-pin DIMM, SODIMM, Mini-
DIMM
DIMM and
Micro-DIMM.[2]
Full-height 288-pin DDR4 DIMMs are slightly taller than their DDR3
counterparts at 1.23 inches (31 mm). Similarly, VLP DDR4 DIMMs
are also marginally taller than their DDR3 equivalent at nearly 0.74
inches (19 mm).[3]
As of Q2 2017, Asus has had a
PCI-E
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
M.2
NVMe
NVMe solid-state drives. However, it cannot use common
DDR type ram and does not have much support other than Asus.[citation
needed]
See also[edit]
Electronics portal
Dual in-line package
Dual in-line package (DIP)
Memory scrambling
Memory geometry – logical configuration of RAM modules
(channels, ranks, banks, etc.)
NVDIMM – non-volatile DIMM
Row hammer
Rambus
Rambus in-line memory module (RIMM)
Single in-line memory module
Single in-line memory module (SIMM)
Single in-line package
Single in-line package (SIP)
Zig-zag in-line package
Zig-zag in-line package (ZIP)
References[edit]
^ Temperature Sensor in
DIMM
DIMM memory modules
^
JEDEC
JEDEC MO-269J Whitepaper., accessed Aug. 20, 2014.
^
JEDEC
JEDEC MO-309E Whitepaper., accessed Aug. 20, 2014.
External links[edit]
Wikimedia Commons has media related to DIMM.
How to Install PC Memory guides
Very Low Profile (VLP) DDR2 Whitepaper (PDF)
v
t
e
Dynamic random-access memory
Dynamic random-access memory (DRAM)
Asynchronous
FPM RAM
EDO RAM
Synchronous
SDRAM
Fast Cycle DRAM (FCRAM)
RLDRAM
DDR SDRAM
Mobile DDR
Mobile DDR (LPDDR)
DDR2 SDRAM
DDR3 SDRAM
DDR4 SDRAM
DDR5 SDRAM
High Bandwidth Memory
HBM2
HBM3
Hybrid Memory Cube
Graphics
VRAM
WRAM
MDRAM
SGRAM
GDDR2
GDDR3
GDDR4
GDDR5
GDDR6
Rambus
RDRAM
XDR DRAM
XDR2 DRAM
Memory modules
SIMM
DI