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Form Factors: Computer memory modules and pin configurations

In this installment of "Computer Memory for your Windows environment", contributor Bernie Klinder reviews computer memory's form factors, its four computer memory modules and their pin configurations.

When looking at computer memory, the first thing you will notice is its form factor or the size of the memory module and its pin configuration. Many motherboards can accept only one type of computer memory form factor, but there are several systems that allow a choice.

  • SIMM (single in-line computer memory module). This early form factor for computer memory is typically seen only in legacy systems. The first SIMM modules had 30 pins and transferred data 8 bits at a time. As 32-bit computing developed, wider 72-pin SIMMs were developed that could transfer data at 32 bits.

  • DIMM (dual in-line computer memory module). DIMMs look similar to SIMMs, except that the DIMMs are longer (168 pins), and the pins on the opposing sides of the computer memory module are electrically isolated from each other. The 168-bit DIMMs transfer data at 64 bits at a time and are commonly found in Pentium and Athlon systems. Newer DDR DIMMs have 184 pins. DDR2 DIMMs may have 200 or 240 pins.

  • RIMM (a trademarked name for the 184-pin Direct Rambus Memory Module). These modules look similar to DIMMs but generate more heat because they provide faster access and transfer speeds. RIMMs come with an aluminum heat spreader that covers the module. Despite having the same number of pins (184) as a DDR DIMM, a RIMM can only be used on motherboards or systems specifically designed for RIMMs.

  • SO DIMM (small outline) and MicroDIMM. Laptops commonly use SO DIMMs. Smaller sub-notebook devices typically use MicroDIMMs. There is also a similar Rambus version called a SO-RIMM.

The most common memory form factor you're likely to encounter today in workstations or servers is the DIMM.

Computer memory for your Windows environment

 Form Factors: Computer memory modules and pin configurations
 Memory Types
 Types of DRAM
 Error Correcting Code and Parity

Bernie Klinder, MVP, consultant
Bernie Klinder is a technology consultant for a number of Fortune 500 companies. He is also the founder and former editor of, a comprehensive resource index for IT professionals who support Microsoft Windows NT/2000/XP/2003 and BackOffice products. For his contributions to the information technology community, Bernie was selected as an MVP (Most Valuable Professional) by Microsoft. Copyright 2004 TechTarget

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