Overview of Read Only Memory
Read Only Memory is abbreviated as ROM which is designed as a semiconductor integrated circuit . The ROM act as a memory storage device where the data in the device is only readable and cannot be modified. The memory in the ROM was a set programming instruction that will be stored at the time of manufacturing. The Program in the ROM device is system level programs which are used to boot the sytem that available in all the system.
ROM is non-volatile type of memory, therefore it is a permanent type of memory. Basically ROM is divided into three types. They are
1. Programmable ROM (PROM)
The PROM are manufactured as a blank memory device and it would be programmed based on the technology applied to used for. The setting of every bit in the device are locked by a fuse or antifuse.The data in the PROM are written only once and it cannot be removed.
2. Erasable Programmable ROM (EPROM)
EPROM are like computer chips, that allow to erase the stored data in the device. The data erasing operation on EPROM is done by using ultra-violent light from a mercury vapour lamp. The re-write of data on EPROM is not limited. To rewrite the data on EPROM some higher voltage should be applied than usual.
3. Electrically Erasable Programmable ROM (EEPROM)
The EEPROM is latest a type of ROM. It is the next level of EPROM used to store some minimum amount of data which must be saved even when power supply is removed. In EEPROM, the user itself can configure the device using system software tools. Flash memory is one of the example for EEPROM device which more economical than traditional EEPROM device.