075 - Types of PC Memory Slot

A memory slot is what allows computer memory to be inserted into the computer. Depending on the motherboard, there may be two to four memory slots and are what determine the type of RAM used with the computer.

Memory sizes:

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 form factor, but there are several systems that allow a choice.

SIMM • (single in-line 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 memory module). DIMMs look similar to SIMMs, except that the DIMMs are longer (168 pins), and the pins on the opposing sides of the 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 form factor you're likely to encounter today in workstations or servers is the DIMM.

Static vs. Dynamic:

In addition to form factor, the chip technology used on the memory module defines the type of RAM.

SRAM • (static RAM). This type of memory maintains data in storage as long as it is powered. Because it is faster and more reliable and expensive than DRAM, SRAM is most often used as cache memory. Earlier forms of SRAM were classified as Async or Sync RAM if they were synchronized with the system clock. The most common type of SRAM today is pipeline burst SRAM, which can operate at higher bus speeds.

DRAM • (dynamic RAM). This type of RAM retains its data by being continuously rewritten every few milliseconds. Like SRAM, the data in storage is volatile, meaning it is lost when the system is not powered. DRAM is the most common type of expandable memory in workstations and servers today, but there are several different types of DRAM.

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