Buffered RAM refers to when the RAM contains a buffer to help the chipset with a large electrical load when a computer has a lot of memory, while unbuffered lacks a buffer. They are two different types of modules, and are not interchangeable as some even use different printed circuit boards. To determine whether or not the RAM is buffered or not, check the leads next to the first notch. If evenly spaced the RAM is buffered. If you attempt to install the wrong type, the stick will not sit properly.