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Read-only memory (ROM) is a type of storage medium that permanently stores data on personal computers (PCs) and other electronic devices.
It contains the programming needed to start a PC, which is essential for boot-up; it performs major input/output tasks and holds programs or software instructions. This type of memory is often referred to as “firmware”—how it is altered has been a source of design consideration throughout the evolution of the modern computer.
Because ROM is read-only, it cannot be changed; it is permanent and non-volatile, meaning it also holds its memory even when power is removed. By contrast, random access memory (RAM) is volatile; it is lost when power is removed.
The use of the similar term “non-volatile memory” is applicable here (more on that later.) One could say that ROM is, in a sense, “stateful” in its enduring state, where RAM is “stateless.”
In a typical modern computer, there are numerous ROM chips located on the motherboard and a few on expansion boards. The chips are essential for the basic input/output system (BIOS), boot up, reading and writing to peripheral devices, basic data management and the software for basic processes for certain utilities.
ROM may also be referred to as maskROM (MROM). MaskROM is a read-only memory that is static ROM and is programmed into an integrated circuit by the manufacturer. An example of MROM is the bootloader or solid-state ROM, the oldest type of ROM.
The history of read-only memory shows how this type of static memory has worked in engineering over the life cycle of the conventional computer.
Read-only memory was pioneered by machines like Mauchly and Eckert’s Electronic Numerical Integrator and Computer or ENIAC in 1948, and then incarnated in integrated circuits in the 1960s. In earlier personal computers, tools like BASIC interpreters were used to implement read-only memory. The use of BIOS ROM in IBM compatible computers (mentioned above) also became common.
Read-only memory is also important in the context of non-volatile memory as a whole.
Non-volatile memory is any kind of memory that is stateful and does not get erased at the end of a live user session. Another way to say this is that non-volatile memory is enduring, and more permanent than temporary.
Experts classify non-volatile memory as one of two fundamental types—mechanically addressed non-volatile memory, and electrically addressed non-volatile memory. The conventional hard drive is an example of mechanical non-volatile memory, and solid-state technology represents electrical non-volatile memory.
The earliest kinds of read-only memory were engineered in such a way that they were not changeable in the field. In order to change the read-only memory, computers had to be shipped back to manufacturers.
Over time, designers begin to experiment with more flexible forms of read-only memory such as the development of electrically erasable programmable ROM or EEPROM in 1971.
Later, Toshiba came up with something called NAND flash, which was aimed at both hard drives and read-only memory resources.
Eventually, something called flash ROM emerged. Flash ROM is more changeable than other earlier types of read-only memory, and accommodates more versatile use. It is now built into a range of Internet of Things devices.