Alternatively referred to as a FPROM (field programmable read-only memory) or OTP (one-time programmable) chip, PROM or Programmable ROM is short for Programmable Read Only Memory and is a computer memory chip first developed by Wen Tsing Chow in 1956 that is capable of being programmed once after it has been created. Once the PROM has been programmed, the information written is permanent and cannot be erased or deleted. A good example of a PROM in a computer is the computer BIOS in early computers.
When the PROM is created it ships with all bits reading as "1" and during the programming any bit that needs to be changed to a 0 is etched or burned into the chip using a device known as a gang programmer. Below is an example of a gang programmer from Advin that programs multiple ROM chips at one time.
If a PROM has been programmed and has an error or needs updated the chip is discarded and a new PROM is created and replaces the old chip. A variation of the PROM is an EPROM, which is a PROM that can be erased and reporgrammed without being replaced.