Compatibility of RAM is tricky and requires some research.
Random access memory (RAM) is perhaps the easiest computer component to upgrade, even on most laptops. However, before upgrading or replacing RAM, first determine the computer's RAM compatibility.
DIMM Type
Dual in-line memory module (DIMM) is the technical term for a stick of RAM. These are small, rectangular circuit boards that hold the RAM chips. For a desktop, use a regular DIMM. Laptops use small-outline dual in-line memory modules (SO-DIMM), which are shorter in length than desktop RAM. Laptop RAM is incompatible with desktop RAM and vice-versa.
RAM Type
Common RAM types include double-data rate (DDR), DDR2, and DDR3. Those RAM types all use one notch on the bottom, placed in slightly different locations, which prevent incompatible RAM from being installed on a motherboard.
RAM Speeds
The speed of RAM is measured in megahertz (MHz). Slower RAM is still compatible on a motherboard rated for a higher speed, but note that the RAM will only work as fast as it is rated. Generally, so long as the RAM is the correct DIMM type and RAM type, the speed and capacity is compatible as well.
ECC & Registered Types
Servers use slightly different kinds of RAM that, at first glance, look exactly the same. Some use Error Correction Codes (ECC) RAM, which is not compatible with desktop computers. Likewise, Registered RAM includes an extra chip on the stick, and it is for servers. When buying RAM for a desktop or laptop, be careful not to accidentally purchase either type.
Tags: in-line memory, slightly different, with desktop