A SO-DIMM, or small outline dual in-line memory module, is a type of computer memory

Computer memory

In computing, memory refers to the physical devices used to store programs or data on a temporary or permanent basis for use in a computer or other digital electronic device. The term primary memory is used for the information in physical systems which are fast In computing, memory refers to the...

 built using integrated circuits.

SO-DIMMs (also written SODIMMs) are a smaller alternative to a DIMM

DIMM

A 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...

, being roughly half the size of regular DIMMs. SO-DIMMs are often used in systems which have space restrictions such as notebook

Laptop

A laptop, also called a notebook, is a personal computer for mobile use. A laptop integrates most of the typical components of a desktop computer, including a display, a keyboard, a pointing device and speakers into a single unit...

s, small footprint PCs (such as those with a Mini-ITX

Mini-ITX

Mini-ITX is a 17 x 17 cm low-power motherboard form factor developed by VIA Technologies in 2001. Mini-ITX is slightly smaller than microATX. Mini-ITX boards can often be passively cooled due to their low power consumption architecture, which makes them useful for home theater PC systems,...

 motherboard

Motherboard

In personal computers, a motherboard is the central printed circuit board in many modern computers and holds many of the crucial components of the system, providing connectors for other peripherals. The motherboard is sometimes alternatively known as the mainboard, system board, or, on Apple...

), high-end upgradable office printers

Computer printer

In computing, a printer is a peripheral which produces a text or graphics of documents stored in electronic form, usually on physical print media such as paper or transparencies. Many printers are primarily used as local peripherals, and are attached by a printer cable or, in most new printers, a...

, and networking hardware

Networking hardware

Networking hardware typically refers to equipment facilitating the use of a computer network. Typically, this includes routers, switches, hubs, gateways, access points, network interface cards, Networking cables, network bridges, modems, ISDN adapters, firewalls and other equipments.In the most...

 like routers.

Visual identification

Most types of SO-DIMMs can be recognized at a glance by the distinctive notches used to “key” them for different applications:

• 100-pin SO-DIMMs have two notches,
• 144-pin SO-DIMMs have a single notch near (but not at) the center, and
• 200-pin SO-DIMMs have a single notch nearer to one side. The exact location of this notch varies (read below.)

Variants of 200-pin SO-DIMMs

The 200-pin SO-DIMM notch is in one of three locations:

• If the notch is located away from the center, it indicates the DDR
  Double data rate
  In computing, a computer bus operating with double data rate transfers data on both the rising and falling edges of the clock signal. This is also known as double pumped, dual-pumped, and double transition....
  
   class of memory.
• When the notch is located nearer the center of the board, it generally (but not always) indicates that the RAM is of the DDR2 type.

These two types of memory are not interchangeable. The different notch locations are designed to prevent cross-installation. Keep this in mind when attempting to visually identify 200-pin SO-DIMM modules.

This variance is designed to prevent coupling of memory and controllers of different DDR generations due to electrical incompatibility.

General characteristics

SO-DIMM measure at 6.76 cm in length and a width of 3.175 cm with a maximum total depth of 0.38 cm.

SO-DIMMs are more or less equal in power and voltage rating to DIMMs, and as memory technology moves forward and despite their smaller size, SO-DIMM technology allows for performance speeds as high as the those of the larger DIMMs (clock speeds such as 400 MHz PC-3200, for example, and CAS latency

CAS Latency

Column Address Strobe latency, or CL, is the delay time between the moment a memory controller tells the memory module to access a particular memory column on a RAM memory module, and the moment the data from given array location is available on the module's output pins...

 such as 2.0, 2.5, and 3.0) and capacity (512MB, 1GB, etc.).

DDR2 SO-DIMM memory modules commonly have clock speeds from 200 MHz up to 800 MHz PC2-6400.

The latest 204-pin SO-DIMMs can contain DDR3 SDRAM, with specifications such as PC3-6400, PC3-8500, PC3-10600, and PC3-12800.

External links

• How to Install PC Memory Guides