16 Facts About ROM

Data stored in ROM cannot be electronically modified after the manufacture of the memory device.

Strictly speaking, read-only memory refers to memory that is hard-wired, such as diode matrix or a mask ROM integrated circuit, which cannot be electronically changed after manufacture.

In 1967, Dawon Kahng and Simon Sze of Bell Labs proposed that the floating gate of a MOS semiconductor device could be used for the cell of a reprogrammable ROM, which led to Dov Frohman of Intel inventing erasable programmable read-only memory in 1971.

The 1971 invention of EPROM essentially solved problem 3, since EPROM can be repeatedly reset to its unprogrammed state by exposure to strong ultraviolet light.

Electrically erasable programmable read-only memory, developed by Yasuo Tarui, Yutaka Hayashi and Kiyoko Naga at the Electrotechnical Laboratory in 1972, went a long way to solving problem 4, since an EEPROM can be programmed in-place if the containing device provides a means to receive the program contents from an external source (for example, a personal computer via a serial cable).

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Flash memory, invented by Fujio Masuoka at Toshiba in the early 1980s and commercialized in the late 1980s, is a form of EEPROM that makes very efficient use of chip area and can be erased and reprogrammed thousands of times without damage.

Consequently, ROM could be implemented at a lower cost-per-bit than RAM for many years.

For example, the Commodore 64 included 64 KB of RAM and 20 KB of ROM containing a BASIC interpreter and the KERNAL operating system.

In modern PCs, "ROM" is used to store the basic bootstrapping firmware for the processor, as well as the various firmware needed to internally control self-contained devices such as graphic cards, hard disk drives, solid state drives, optical disc drives, TFT screens, etc.

Since ROM cannot be modified, it is only suitable for storing data which is not expected to need modification for the life of the device.

Mask ROM is a read-only memory whose contents are programmed by the integrated circuit manufacturer.

Per bit, mask ROM is more compact than any other kind of semiconductor memory.

Since the cost of an integrated circuit strongly depends on its size, mask ROM is significantly cheaper than any other kind of semiconductor memory.

Design errors are costly: if an error in the data or code is found, the mask ROM is useless and must be replaced in order to change the code or data.

Classic mask-programmed ROM chips are integrated circuits that physically encode the data to be stored, and thus it is impossible to change their contents after fabrication.

Timespan over which a ROM remains accurately readable is not limited by write cycling.