In computing, memory refers to the physical devices used to store programs or data on a temporary or permanent basis for use in a computer or other digital electronic device. PC memory is one of the most integral components of any personal computer. The memory allows programs (like your operating system) to function. When you execute a program, that program draws from your computer's available memory. The more memory you have, the faster a program will be able to run.
Desktop memory is a kind of Random Access Memory (RAM) that is used on desktop computers. RAM is generally measured in gigabytes, reads and writes data that is used by the computer's processor. When you click a program to open it, your desktops processor stores the data for the in-use program in RAM, where the data stays intact until the opened program is closed.
While they perform the same function, desktop and laptop memory are different in that desktop memory is physically bigger. You will commonly find Dual In-line Memory Modules (DIMMs) in desktops.
There are a large number of RAM types available for desktop computer systems. The most commonly used types today are DIMMs (Dual In-Line Memory Module) and these are the small circuit boards that holds memory chips. DIMMs are standard in desktop computers, and common types of DIMMs are SDRAM, DDR SDRAM, DDR2 SDRAM and DDR3 memory. These are not backward compatible.
Physically, the recent DDR3 memory chips have 240 pins. This is the same as DDR2, although electrically the two forms are incompatible, along with having different locations for their key notches. The original DDR format has only 184 pins. As far as power consumption goes, the DDR line has become more energy efficient as it progresses: 1.5 volts for DDR3 versus 1.8V for DDR2 and 2.5V for DDR.
What is important to know about memory is that, the more of it the better.