ROM - Read-Only Memory

ROM (Read-Only Memory)
Manufacturer:	Intel®	Speed:	70ns
Year Introduced:	1971	Frequency:	4.77MHz
Burst Timing:		Pins:	28-44 DIP
Voltage:	2.7v~5.5v	Bandwidth:

Types of ROM
ROM:	Read-only memory. The “1”s and “0”s are permanent and created at the silicon foundry. Only used for circuits needed in the tens of thousands and after many prototypes.
PROM:	Programmable read-only memory. A hardware device connected to a PC can program the ROM, but it is write-once.
EPROM:	Erasable programmable read-only memory. A PROM that can be erased by exposure to ultraviolet light.
EEPROM:	Electrically erasable programmable read-only memory. A PROM that can be erased by high voltages.
Semiconductor-based Memory that contains instructions or data that can be read but not modified. (Generally, the term ROM often means any read-only device, as in CD-ROM for Compact Disk, Read Only Memory.) Once data has been written onto a ROM chip, it cannot be removed and can only be read. Unlike main Memory (RAM), ROM retains its contents even when the computer is turned off. ROM is referred to as being nonvolatile, whereas RAM is volatile. Most personal computers contain a small amount of ROM that stores critical programs such as the program that boots the computer. In addition, ROMs are used extensively in calculators and peripheral devices such as laser printers, whose fonts are often stored in ROMs. Electrically Erasable Programmable Read-Only Memory (EEPROM) Machines with flash BIOS capability use a special type of BIOS ROM called an EEPROM; this stands for "Electrically Erasable Programmable Read-Only Memory". As you can probably tell by the name, this is a ROM that can be erased and re-written using a special program. This procedure is called flashing the BIOS and a BIOS that can do this is called a flash BIOS. The advantages of this capability are obvious; no need to open the case to pull the chip, and much lower cost. EEPROM is similar to flash memory (sometimes called flash EEPROM). The principal difference is that EEPROM requires data to be written or erased one byte at a time whereas flash memory allows data to be written or erased in blocks. This makes flash memory faster. Flash memory works much faster than traditional EEPROMs because it writes data in chunks, usually 512 bytes in size, instead of a byte at a time.

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Last Update: 5:26 PM 7/31/01

Types of ROM