The Various Types of RAM

DDR RAM, EDO, FPM, SDRAM, SIMM, DIMM… it can all be a bit confusing, especially if this is your first exposure to computer hardware.

These terms all describe different types of RAM modules that each differ in their physical properties. Generally, RAM modules fall into two types of categories:

SIMM (Single In-line Memory Module)
DIMM (Dual In-line Memory Module)

SIMMs were first released in 1983 and are not commonly used today. With the advent of 64-bit processors, the 32-bit wide SIMMs had to be installed in pairs to remain compatible. Consequently, SIMMs have been replaced by 64-bit wide DIMMs, which can be installed individually.

EDO (Extended Data Out) and FPM (Fast Page Mode) are types of SIMM, while DDR (Dual Data Rate) and SDRAM (Synchronous Dynamic RAM) fall into the DIMM category. There’s also a type called SO-DIMMs (Small Outline DIMMs) which are smaller in size and commonly found in laptops.

You might have noticed that DDR RAM comes in different versions, namely DDR, DDR2, DDR3, and DDR4. These are increasingly faster RAM modules that are not compatible with each other.

http://www.wisecleaner.com/think-tank/183-The-Various-Types-of-RAM.html