Read only memory(ROM)

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Here, on the ROM type of memory data in this memory can only be read, but no writing is allowed. This type of memory is used to store permanent programs. It is a nonvolatile memory, means data will not erase even if the power will be off.

Types of ROM memory is as follows:

1. Masked ROM
2. PROM (Programmable read only memory)
3. EPROM (Erasable programmable read only memory)
4. EEPROM

Masked ROM

On masked ROM at the time of manufacturing, the program or data are permanently installed as per requirement. The data cannot be altered. Permanent recording process is very expensive but economic for large quantities.

PROM (Programmable read only memory)

Its basic function is the same as that of masked rom. But in PROM, we have fuse links. The fuse can be burnt or kept intact depending upon the bit pattern, this job is performed by PROM programmer. It uses a high current pulse between two lines to do this. As a result of high current, the fuse will get burnt; effectively making two lines open. When a PROM is programmed, we will not ne able to change connections, only a facility provided over masked ROM is, the user can load his program in it. A chance of re-growing of the fuse and changes the programmed data because of aging is a disadvantage.

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EPROM (Erasable Programmable Read Only Memory)

The EPROM is programmable by the user. It uses MOS circuitry to store data. 1’s and 0’s are store in form of charge. The data stored in all memory locations can be erased by exposing the memory to ultraviolet light. A quartz window is provided which is covered during normal operation for ultraviolet light. It can be reprogrammed by using EPROM programmer when erasing. In a project developed and for experiment use, we use this type of memory. As it can be programmed erased and reprogrammed, it is a great advantage. But all the data get erased even if we want to change single data bit, and it is a disadvantage of EPROM.

EEPROM

Electrically erasable programmable read only memory. Here the erasing is done by electrical signals instead of ultraviolet light and the rest is almost the same as EPROM. The memory location can be selectively erased and reprogrammed in EEPROM. But it is not commonly used as the manufacturing process is complex.

Conclusion

The computer always loads data from read only memory(ROM). It is a nonvolatile device, and it is used in computer and other electronic devices. So, in digital world or in use of computer ROM is a very important thing.

Source

1. Fundamentals of Computer Technologies

• https://link.springer.com/chapter/10.1007/978-3-319-13626-4_9