What Is the Difference Between DIMM and SDRAM?

By Dennis Costa

Computer memory represents one of the most potentially confusing components in modern PCs. The sheer amount of terms, types and acronyms can be daunting even for experienced computer users. For instance, what do SDRAM and DIMM mean, anyway, and what is the difference between the two?

Defining Memory

First, SDRAM represents a type of random access memory (RAM) in the computer. Memory is basically where you store the information temporarily for quick and easy access. If a computer's chip is the chef that "cooks" or processes the data and the hard disk is the pantry where all of the ingredients are stored, then memory is like the counter where the chef places the necessary ingredients within easy reach.

SDRAM

Let's now find out what SDRAM really means. The SD stands for "synchronous dynamic," synchronous in the sense that it keeps the same rhythm of clock cycle as other components in a computer's CPU (central processing unit), like the various buses and the chipset itself. "Dynamic" means that information can be easily added or taken off the memory module. SDRAM is one of the most common types of RAM around, according to the book "Upgrading & Repairing PCs."

Memory Modules

Memory comes in what are best described as "wafers." They are thin, elongated strips full of electronics. Such a configuration was developed because early computer memory was designed as a chip that was plugged in right in the motherboard, the circuit board where the main processor is located. These chips would tend to disengage by themselves with changes in temperature. Another method was soldering the chips directly onto the motherboard, but this also caused problems. The development of memory modules became the solution, with a small board that plugs in directly with the connector soldered on the motherboard.

SIMMs and DIMMs

Early memory modules had a single row of electrical contacts, and thus were called single inline memory modules, or SIMMs. Later modules came with two rows of contacts and were called dual inline memory modules, or DIMMs. Another short-lived type of memory module was the Rambus inline memory module, or RIMM. So in reality, a DIMM basically describes the type of connection a memory module has to the motherboard, while a term like SDRAM describes the memory module itself.

Types of DIMMs

However, both terms are very related to each other in terms of their function because a memory module can send and receive information as fast as its connection allows. For each type of SDRAM that exists, there is a different type of DIMM connection. For instance, SDR (single data rate) SDRAM modules have DIMMs with 168 pins, while faster DDR (double data rate) SDRAM modules have 184 pins in its DIMM connectors. The industry standard in 2010, DDR2 and DDR3 modules, have 240 pins.