Programmable Read-Only Memory or PROM is a computer chip used to store information that has had ithis nformation loaded into it and then fixed or 'burned in' so that it will not be lost when the chip or the device loses power or is turned off. PROMs are used to store programs and data used when a device containing a computer processing chip is turned on. At boot-up, information is loaded from the PROM into active memory and then executed.
PROM was the second type of 'permanent' storage developed by computer chip manufacturers to reduce the cost of making chips. They were cheaper to make because a manufacturer could make one chip that could store any internal data configuration that was necessary. This reduced the number of production lines.
Compare this with ROM.
See also:
The evolution of computer ROMs.