Random Access Memory is a form of memory that can be read without having to begin at the first address, then the second address, then the third, and so on. This is a carryover from when most memory was Serial Access, such as magnetic tape, paper tape, or punched cards. The on-board memory computers use for temporary storage is Random Access Memory, but on chips, instead of a hard disc drive.
Read Only Memory is exactly what the name implies, it can only be read, not written to. A CD-ROM is a form of memory, as is a chip on the motherboard which is used to store instructions for the Central Processor Unit. RAM is your computer's temporary storage space. RAM is really the computer's short-term memory. As such, it remembers everything that the computer needs to process the data into information, such as data that has been entered and software instructions, but only when the computer is on. This means that RAM is an example of volatile storage. When the power is off, the data stored in RAM is cleared out. This is why, in addition to RAM, systems always include nonvolatile storage devices for permanent storage of instructions and data when the computer is powered off. Hard disks provide the greatest nonvolatile storage capacity in the computer system.