EPROM
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VariousEPROMS.png
An EPROM, or erasable programmable read-only memory, is a type of computer memory chip that retains its data when its power supply is switched off. In other words, it is non-volatile. It is programmed by an electronic device that supplies higher voltages than those normally used in electronic circuits. Once programmed, an EPROM can be erased only by exposing it to strong ultraviolet light. EPROMs are easily recognisable by the transparent window in the top of the package, through which the silicon chip can be seen, and which admits UV light during erasing.
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A programmed EPROM retains its data for about ten to twenty years and can be read an unlimited number of times. The erasing window must be kept covered to prevent accidental erasure by sunlight. Old PC BIOS chips were often EPROMs, and the erasing window was often covered with a label containing the BIOS publisher's name, the BIOS revision, and a copyright notice.
Some microcontrollers, often those from before the era of Flash Memory, use EPROM to store their program. This is useful for development, as using one-time programmable devices would be horribly wasteful for debugging.
The EPROM was invented by engineer Dov Frohman.
EPROMs come in several sizes both in physical packaging as well and storage capacity
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EPROM Type
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Size - bits
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Size - bytes
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Length (hex)
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Last address (hex)
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2716, 27C16
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16 kbit
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2KBytes
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800
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007FF
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2732, 27C32
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32 kbit
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4KBytes
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1000
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00FFF
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2764, 27C64
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64 kbit
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8KBytes
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2000
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01FFF
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27128, 27C128
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128 kbit
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16KBytes
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4000
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03FFF
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27256, 27C256
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256 kbit
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32KBytes
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8000
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07FFF
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27512, 27C512
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512 kbit
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64KBytes
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10000
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0FFFF
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27C010, 27C100
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1Mbit
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128KBytes
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20000
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1FFFF
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27C020
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2 Mbit
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256 kbytes
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40000
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3FFFF
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27C040
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4 Mbit
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512 kbyte
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80000
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7FFFF
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NOTE: 27x series EPROMs containing a C in the name are CMOS based, without the C are NMOS
See also
- Programmable read-only memory
- EEPROM, like EPROM but electrically erasable
- Flash memoryda:EPROM
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