RAM refers to temporary memory that can be accessed and altered over and over again. RAM can be accessed by any programs that need to store information temporarily as part of their operations. The more RAM a computer has, the more processing a CPU can do without accessing the hard disk, making the computer much faster. The data stored on RAM is erased once the program finishes its task, or when the power to the computer is cut.
ROM is a permanent memory chip that can be read by a machine, but not written on. Unlike RAM, the data stored on ROM is still there whether the computer has power or not. A common example of ROM is the firmware your computer uses to boot up. You cannot access or use that portion of a computer’s memory for anything else. Another familiar example is a CD-ROM. Once it is burned, the data on the CD cannot be altered.
To put it simply, the difference between RAM and ROM is that ROM is only written once and thereafter can only be read, whereas RAM can be written, read and overwritten again and again.