Read-Only Memory (ROM)
Read Only Memeory shortly known as ROM is a major type of memory that is used in computers and other electronic devices. This is a type of data storage whose contents can be accessed by the user but cannot be altered by the user. It normally can only be read. There are two main reasons that read-only memory is used for certain functions within the PC. The most common example is the system BIOS program, which is stored in a ROM called the system BIOS ROM. ROM can be classified into three types. They are:
Programmable ROM (PROM):
Programmable Read Only Memory - a type of memory that may be programmed once and then the data can not be changed again. Programming a PROM is also called burning, just like burning a CD-R, and it is comparable in terms of its flexibility.
Erasable Programmable ROM (EPROM):
EPROM is a special type of memory that can be erased and reprogrammed. The contents of the EPROM can be cleared using the ultra violet light. This makes it possible to reprogram the memory. Ultraviolet light of a specific frequency can be shined through this window for a specified period of time, which will erase the EPROM and allow it to be reprogrammed again. To write to and erase an EPROM, you need a special device called a PROM programmer or PROM burner.
Electrically Erasable Programmable ROM (EEPROM):
EEPROM - Short for Electrically Erasable Programmable Read Only Memory. This a special nonvolatile memory that can be erased and (re)programmed multiple times electrically. This is the most flexible type of ROM, and is now commonly used for holding BIOS programs. EEPROM is very similar to flash memory. The main difference between EPROMs and EEPROMs is the way that they discharge the charge stored in the floating gate.