Read-Only Memory (ROM)

Read Only Memory

Read-Only Memory (ROM)

Read-Only Memory (ROM) refers to the memory chips storing data that only can be read. The data on ROM chips cannot be modified-hence, the name read-only. Read-Only Memory (ROM) is nonvolatile.  Its innards are not gone when power is detached from the computer.

Read Only Memory

Read-Only Memory (ROM) chips contain data, instructions, or information that is recorded permanently. For example, ROM contains the basic input/output system (BIOS), which is a sequence of instructions the computer follows to load the operating systems and other files when you first turn on the computer. Many other devices also contain ROM chips. For example, ROM chips in many printers contain data for the font.

Manufacturers of ROM chips often recorded the data, instructions, or information on the chips when they manufactured the chip. These ROM chips, called firmware, contain eternally written data, commands, or material. The BIOS is firmware that contains the computer’s setup directions.


PROM is the acronym for programmable Read-only memory. In computer science, a type of Read-Only Memory (ROM) allows data to be written into the device with hardware called a PROM programmer. Subsequently, a PROM has been programmed, it is devoted to that data, and it cannot be reprogrammed. Because ROMs are lucrative only when produced in large volumes, PROMs are used during the prototyping phase of the design. New PROMs can be created and discarded as needed until the design is perfect.


EPROM is the acronym for erasable programable read-only memory. Also called reprogrammable read-only memory (RPROM).  EPROMs are nonvolatilizable memory chips that are programmed after they are factory-made. EPROMs are a decent way for hardware sellers to put viable or continuously fluctuating code into a prototype system when the cost of producing many PROM chips would be prohibitive. EPROMs differ from PROMs in that they can be erased, usually by removing a protective cover from the top of the chip package and exposing the semiconductor material to ultraviolet light, and can be reprogrammed after having been removed. Although EPROMs are more expensive than PROMs, they can be more lucrative in the long run if many changes are needed.

Flash Memory

Flash Memory, also known as flash Read-Only Memory (ROM) or flash RAM, is a type of nonvolatile memory that can be erased electronically and reprogrammed. Many current computers also used flash BIOS. With flash BIOS, the computer easily can update the contents of the BIOS chip, if necessary.

Flash memory chips stock data and programs on many handheld computers and devices, such as digital cellular telephones, printers, set-top boxes, digital cameras, automotive devices, digital voice recorders, and pagers. Flash memory cards are stored on a removable device instead of a chip. Removable flash memory allows users to transfer data and information conveniently from these small devices to their desktop computers. Flash memory is available in sizes up to 128 MB.


Another type of memory chip in the system unit is a complementary metal-oxide semiconductor memory. complementary metal-oxide semiconductor memory, abbreviated CMOS (pronounced SEE-moss), store configuration information about the computer. This information includes the type of disk drives, keyboard, and monitor; the current date and time; and other startup information needed when you turn on the computer.

CMOS chips use battery power to remember data even when the power to the computer is off. Battery-backed CMOS memory thus keeps the calendar, date, and time current even when the computer is off. Unlike standard Read-Only Memory (ROM), the computer can change information in CMOS, such as when you change from standard time to daylight saving time or when you add new hardware devices to the computer.

Memory Access Time

Access time is the quantity of time its takings the processor to read data, directions, and information from memory. A computer access time straight affects how fast the computer process data. Manufacturers use a variety of terminology to state access time. Some use functions of second, which for memory, occurs in nanoseconds. A nanosecond (abbreviated ns) is one billionth of a second. A nanosecond is extremely fast. Other manufacturers state access time in MHz, e.g., an 83 MHz SDRAM. If a manufacturer states access time in megahertz, you can convert it to nanoseconds by dividing the megahertz number into 1 billion ns. For example, 133 MHz equals approximately 7.5 ns.

Access time Terminology

Term Abbreviation Speed
Millisecond MS One-thousandth of a second
Microsecond US One-millionth of second
Nanosecond Ns One-billionth of second
Picosecond Ps One-trillionth of a second


The access time (speed) of memory contributes to the overall performance of the computer. SDRAM chips can have access times up to 133 MHz (7.5 ns) the faster RDRAM chips can have access times up to 800 MHz (1.25 ns). Read-only memory (ROM) access times range from 25 to 250 ns.  While access times of memory greatly affect overall computer performance, manufacturers and retailers usually list a computer’s memory in terms of its size and its access time. Thus, an advertisement might describe a computer as having 32 MB of SDRAM expandable to 512 MB.

You can expand the memory capacity in a number of ways, such as installing additional memory in an expansion slot or inserting a memory card into a card slot. (Read More…..)


17 thoughts on “Read-Only Memory (ROM)

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