Computer memory, also known as RAM (random access memory) is the place in the computer where the operating system stores information about applications and data in current use so that they can be quickly reached by the computers processor.
RAM is much faster to read from and write to than the other kinds of storage in a computer, the hard disk, floppy disk, and CD-ROM. However, the data in RAM only stays there only as long as your computer is running. When you turn the computer off, RAM loses its data. When you turn your computer on again, your operating system and other files are once again loaded into RAM, usually from your hard disk. There is technology in the works to fix this problem, but that will take a while to reach the rest of us.
Computer memory can be compared to a persons short-term memory, and the hard disk to the long-term memory. The short-term memory focuses on work at hand, but can only keep so many facts in view at one time. Long term memory is much more abundant, and lasts much longer.
Computers work much like this as well, RAM takes care of the current workload, and the hard drive stores long term data. The faster these two can work, the faster your computer can calculate.
There are three types of computer memory.
SDRAM – The slowest, yet cheapest
DDR – Fast and efficient, and very cost effective
DDR2 – The fastest available memory to date
RDRAM – Use to be the fastest and the most expensive, generally a pain since they have to be used in pairs
The Motherboard must be compatible with the type of memory you want to use. Several Motherboard companies produce Motherboards with SDRAM and DDR slots, which can NOT be used at the same time, but it is nice to have a choice of what you can use.
Each type of RAM also has various speeds at which it works, and the Motherboard must also support these speeds. DDR for example currently comes in either pc2100, pc2700, & pc3200, while DDR2 comes in pc3200, pc4200, pc5400, pc6400, & pc8000.
RAM also works at various megahertz, limited by the megahertz that the Front Side Bus on your motherboard works (the Front Side Bus, or FSB, is the channel on the motherboard used to transfer information from the CPU to the RAM) so if you have RAM that works at 500 megahertz, and the FSB of your motherboard only runs at 333 megahertz, then 333 megahertz is the fastest your memory can run as well.
One very important note about computer memory, is you do not want to mix various speeds of memory, because the Motherboard will take the slowest speed and dummy all the rest of the fast memory to that slower speed. Here's an example:
You have three sticks of DDR computer memory in your computer, 2 pc2700's, and 1 pc2100. The Motherboard slows down the 2 pc2700's to be the speed of the pc2100, so that they're all working at the same speed.
While this scenario works ok, it is not a good idea, because you have lost the value of the higher speed RAM.