ROM: PROM, EPROM, EEPROM : CISSP Domain – Asset Security

Ahh the various types of ROM.  So much fun, right?  Okay here goes . . .

ROM stands for read only memory. It’s where the BIOS lives.  It’s a non volatile chip: In other words, when you reboot your computer it will still be there.

There are three kinds of ROM:

PROM – Programmable Read Only Memory:  is the granddaddy of them all.  It can only be written too once.

EPROM – Electronically Programmable Read Only Memory: With the use of ultraviolet light you can write to multiple times.  This is where the word “flashing” comes from.

EEPROM – Electronically Erasable Programmable Read Only Memory: This is the modern ROM.  It can be erased.  It can be updated and doesn’t need to be removed to do so.  The most famous kind of EEPROM is a flash memory USB drive.  With this type of ROM you can only write to it one bit at a time.

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