16 Facts About ROM


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

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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.

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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.

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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.

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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.

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

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

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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.

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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.

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

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

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

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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.

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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.

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

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