ROM - Read Only Memory, is similar to RAM because it holds data and computer instructions. But a very important difference is that when the power is off, or the CPU (Central Processing Unit) tells the RAM to "flush" some data out of it, the data in a RAM chip changes or disappears. Read Only means that the data on a ROM device stays there and it stays unchanged. The computer can read the data but it can't "write" any other data into it because it cannot change any of the data on the ROM.

Above is also a special ROM-type computer chip called a BIOS (don't worry, you don't have to remember that one!) chip. It has all the instructions needed to tell the computer itself how to turn on, or "boot up". If the data in that ROM chip changed all the time the computer wouldn't know how to boot up!

Here is a different kind of Read Only Memory device that you are more familiar with. DVD disks and CDs and yes, some disks you use at school that mix audio, video, graphics and sometimes links to websites, are all "READ ONLY" memory (ROM) devices. The information on them never changes. You only can "read" the data, whether it is pictures, music, video or a combination of those.