ROM full form is Read Only Memory. It is a type of computer memory which can only be read. ROM memory is the one that contents of the memory could be read multiple times but could not be written (modified), once it is written. ROM is a non-volatile type of memory and therefore data in it is retained even after the unavailability of power. Read-only memory is useful for storing the various Software/Data that is rarely changed throughout the existence of the system which is also known as firmware. ROM is cheap to produce as compared to other non-transient mediums of storage and therefore experienced widespread adoption and upgradation of the technology.
The ROM full form is Read Only Memory. The concept of read-only memory (ROM) was first introduced by the researcher Robert Dennard in the 1960s. Dennard was a researcher at IBM and the inventor of dynamic random-access memory (DRAM) which is a type of memory that is used in computers and other electronic devices to store data on a temporary basis.
In his research, Dennard reached the realization that it would be beneficial to have a type of memory that could store data permanently and not lose its contents when the power was turned off automatically or manually. He named this type of memory "read-only memory," because it could only be read and not written.
Types of ROM
A ROM consists of the integrated circuits that physically encode the stored data. This makes the data almost impossible to be re-written and therefore maintains the integrity of the data. But many other types of ROM use semiconductor-based solid-state of memory, which allows for the modification of the written data. Different types of ROM technologies available are:
MROM – Mask ROM is a kind of read-only memory that is concealed at the time of the production. Similar to other types of ROM, mask ROM doesn’t allow the user to change the data stored in it further. If it can, the process would be difficult or slow paced.
PROM: PROM full form is Programmable read-only memory. A PROM is shipped as a ROM without any data or software inside it. Therefore, the user is free to program or create any data inside it. But once the data has been written to the PROM, it could longer be written or modified again. It could only be used to read and interpret the data which was initially written to it. The method by which PROM differs from a regular ROM is that a generic ROM has data prewritten on it (BIOS, Embedded systems etc) and the user (or device containing the ROM) could only read it. But since a PROM is empty at the beginning, the custom data could be written to it as per the requirement.
EPROM: EPROM stands for Erasable Programmable read-only memory. The data present on the chip could be erased if the EPROM chip is exposed to strong ultraviolet light for some specific duration. After which the contents of the EPROM are lost and newer versions of data could now be rewritten to it.
EEPROM: EEPROM stands for Electrically Erasable Programmable Read Only Memory. EEPROM builds upon the similar principle of EPROM (ability to re-write data). Moreover, EEPROM allows the stored data to be erased electrically. After which the data could be rewritten easily Electrically. The data is written electrically and the longevity of the EPROM chip keeps on increasing.
FLASH ROM: FLASH ROM is an advanced version of EEPROM. It stores information in a definite arrangement or array of memory cells made from floating-gate transistors. The main advantage of using this memory is that you can delete or write blocks of data around 512 bytes at a particular time. Whereas, in EEPROM, you can delete or write only 1 byte of data at a particular time. So, FLASH ROM memory is faster than EEPROM. This memory can be reprogrammed without removing it from the computer. Its access time is very high, somewhere around 45 to 90 nanoseconds. It is also highly durable and tensile in nature as it can bear high temperature and intense pressure.
Internal Structure of ROM
The internal structure of ROM comprises two basic components: decoder and OR gates. A decoder is a circuit that decodes an encoded structure (such as binary coded decimal, BCD) to a decimal form. So, the input is in binary form, and the output is in the form of decimal. All the OR gates present in the ROM will retain outputs of the decoder as their output.
Advantages of ROM
Various advantages of ROM are mentioned below:
Non-Volatile: ROM does not require a continuous uninterrupted power supply to maintain the data in the device once the data has been written. Therefore it retains the information even after the power is gone.
Cost: ROM is Cost-efficient in nature. Hence, it could be integrated into devices with a feasible budget.
Circuitry: ROM incorporates a simple underlying mechanism and could easily be reproduced without much trouble or technology.
Data Security: Since the data could only be written once, the mechanism inherently provides the protection to the data. Therefore, accidental deletion of data could not happen in ROM.
Disadvantages of ROM
Along with various advantages, ROM has disadvantages associated with it which are mentioned below:
Reading is faster- Data is readable as nanoseconds per bit as opposed to writing data to ROM which is milliseconds per bit
ROM has low storage capacity and hence could only be used to store small and critical data.
