Read-only memory

ROMROMsread-onlyread only memorymemoryRead-only memory (ROM)storage64 MBEAROMfont ROM
Read-only memory (ROM) is a type of non-volatile memory used in computers and other electronic devices.wikipedia
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ROM cartridge

cartridgecartridgesgame cartridge
Data stored in ROM can only be modified slowly, with difficulty, or not at all, so it is mainly used to store firmware (software that is closely tied to specific hardware, and unlikely to need frequent updates) or application software in plug-in cartridges.
A ROM cartridge, usually referred to simply as a cartridge or cart, is a removable enclosure containing ROM designed to be connected to a consumer electronics device such as a home computer, video game console and to a lesser extent, electronic musical instruments.

Firmware

flashflashingautomobile firmware
Data stored in ROM can only be modified slowly, with difficulty, or not at all, so it is mainly used to store firmware (software that is closely tied to specific hardware, and unlikely to need frequent updates) or application software in plug-in cartridges.
Firmware is held in non-volatile memory devices such as ROM, EPROM, or flash memory.

Mask ROM

mask-programmed ROMFixed ROMmask
Strictly, read-only memory refers to memory that is hard-wired, such as diode matrix and the later mask ROM (MROM), which cannot be changed after manufacture.
Mask ROM (MROM) is a type of read-only memory (ROM) whose contents are programmed by the integrated circuit manufacturer (rather than by the user).

Diode matrix

matrixdiode matricesdiode-matrix
Strictly, read-only memory refers to memory that is hard-wired, such as diode matrix and the later mask ROM (MROM), which cannot be changed after manufacture.
It is one of the most popular techniques for implementing a read-only memory.

Programmable read-only memory

PROMPROMsOTP
PROM, invented in 1956, allowed users to program its contents exactly once by physically altering its structure with the application of high-voltage pulses.
It is one type of ROM (read-only memory).

Flash memory

flashNANDflash storage
Flash memory, invented at Toshiba in the mid-1980s, and commercialized in the early 1990s, is a form of EEPROM that makes very efficient use of chip area and can be erased and reprogrammed thousands of times without damage.
This makes it a suitable replacement for older read-only memory (ROM) chips, which are used to store program code that rarely needs to be updated, such as a computer's BIOS or the firmware of set-top boxes.

Non-volatile memory

non-volatilenon-volatile storagenon-volatile memories
Read-only memory (ROM) is a type of non-volatile memory used in computers and other electronic devices. Every stored-program computer may use a form of non-volatile storage (that is, storage that retains its data when power is removed) to store the initial program that runs when the computer is powered on or otherwise begins execution (a process known as bootstrapping, often abbreviated to "booting" or "booting up").
Examples of non-volatile memory include read-only memory, flash memory, ferroelectric RAM, most types of magnetic computer storage devices (e.g. hard disk drives, solid state drives, floppy disks, and magnetic tape), optical discs, and early computer storage methods such as paper tape and punched cards.

Home computer

home computershomehome computing
Most home computers of the 1980s stored a BASIC interpreter or operating system in ROM as other forms of non-volatile storage such as magnetic disk drives were too costly.
Since most systems shipped with the BASIC programming language included on the system ROM, it was easy for users to get started creating their own simple applications.

USB flash drive

flash driveUSB driveflash drives
, NAND has partially achieved this goal by offering throughput comparable to hard disks, higher tolerance of physical shock, extreme miniaturization (in the form of USB flash drives and tiny microSD memory cards, for example), and much lower power consumption.
USB mass storage controller a small microcontroller with a small amount of on-chip ROM and RAM.

Computer hardware

hardwarepersonal computer hardwaredevice
Data stored in ROM can only be modified slowly, with difficulty, or not at all, so it is mainly used to store firmware (software that is closely tied to specific hardware, and unlikely to need frequent updates) or application software in plug-in cartridges.
Read-only memory (ROM), which stores the BIOS that runs when the computer is powered on or otherwise begins execution, a process known as Bootstrapping, or "booting" or "booting up". The BIOS (Basic Input Output System) includes boot firmware and power management firmware. Newer motherboards use Unified Extensible Firmware Interface (UEFI) instead of BIOS.

Booting

bootloaderbootboot loader
Every stored-program computer may use a form of non-volatile storage (that is, storage that retains its data when power is removed) to store the initial program that runs when the computer is powered on or otherwise begins execution (a process known as bootstrapping, often abbreviated to "booting" or "booting up"). Later home or office computers such as the IBM PC XT often included magnetic disk drives, and larger amounts of RAM, allowing them to load their operating systems from disk into RAM, with only a minimal hardware initialization core and bootloader remaining in ROM (known as the BIOS in IBM-compatible computers).
After the power is switched on, the computer is relatively dumb and can read only part of its storage called read-only memory (ROM).

BASIC

BASIC programming languagecompiled BASICBASIC IV
Most home computers of the 1980s stored a BASIC interpreter or operating system in ROM as other forms of non-volatile storage such as magnetic disk drives were too costly.
These machines almost always had a BASIC installed by default, often in the machine's firmware or sometimes on a ROM cartridge.

Computer

computerscomputer systemdigital computer
Read-only memory (ROM) is a type of non-volatile memory used in computers and other electronic devices.
read-only memory or ROM

KERNAL

For example, the Commodore 64 included 64 KB of RAM and 20 KB of ROM contained a BASIC interpreter and the "KERNAL" of its operating system.
KERNAL is Commodore's name for the ROM-resident operating system core in its 8-bit home computers; from the original PET of 1977, followed by the extended but strongly related versions used in its successors: the VIC-20, Commodore 64, Plus/4, C16, and C128.

Commodore 64

C6464Commodore
For example, the Commodore 64 included 64 KB of RAM and 20 KB of ROM contained a BASIC interpreter and the "KERNAL" of its operating system.
The machine used the same case, same-sized motherboard, and same Commodore BASIC 2.0 in ROM as the VIC-20.

BIOS

system BIOSBasic Input/Output Systemsystem
Later home or office computers such as the IBM PC XT often included magnetic disk drives, and larger amounts of RAM, allowing them to load their operating systems from disk into RAM, with only a minimal hardware initialization core and bootloader remaining in ROM (known as the BIOS in IBM-compatible computers).
Originally, BIOS firmware was stored in a ROM chip on the PC motherboard.

Operating system

operating systemsOScomputer operating system
Most home computers of the 1980s stored a BASIC interpreter or operating system in ROM as other forms of non-volatile storage such as magnetic disk drives were too costly.
The first microcomputers did not have the capacity or need for the elaborate operating systems that had been developed for mainframes and minis; minimalistic operating systems were developed, often loaded from ROM and known as monitors.

Microprocessor

microprocessorsprocessorchip
These are in everything from industrial robots to home appliances and consumer electronics (MP3 players, set-top boxes, etc.) all of which are designed for specific functions, but are based on general-purpose microprocessors.
This chip could also arguably lay claim to be one of the first microprocessors or microcontrollers having ROM, RAM and a RISC instruction set on-chip.

ENIAC

Electronic computerElectronic Numerical Integrator And ComputerENIAC (Electronic Numerical Integrator and Computer)
Forms of read-only memory were employed as non-volatile storage for programs in most early stored-program computers, such as ENIAC after 1948. Resistor, capacitor, or transformer matrix ROM, used in many computers until the 1970s. Like diode matrix ROM, it was programmed by placing components at selected locations between a matrix of word lines and bit lines. ENIAC's Function Tables were resistor matrix ROM, programmed by manually setting rotary switches. Various models of the IBM System/360 and complex peripheral devices stored their microcode in either capacitor (called BCROS for balanced capacitor read-only storage on the 360/50 and 360/65, or CCROS for charged capacitor read-only storage on the 360/30) or transformer (called TROS for transformer read-only storage on the 360/20, 360/40 and others) matrix ROM.
A number of improvements were made to ENIAC after 1947, including a primitive read-only stored programming mechanism using the function tables as program ROM, after which programming was done by setting the switches.

CD-ROM

CDCD-ROM drives18x
* Optical storage media, such CD-ROM which is read-only (analogous to masked ROM).
Computers can read—but not write to or erase—CD-ROMs, i.e. it is a type of read-only memory.

IBM Personal Computer XT

XTIBM PC XTPC/XT
Later home or office computers such as the IBM PC XT often included magnetic disk drives, and larger amounts of RAM, allowing them to load their operating systems from disk into RAM, with only a minimal hardware initialization core and bootloader remaining in ROM (known as the BIOS in IBM-compatible computers).
Like the original PC, the XT came with IBM BASIC in its ROM.

Computer data storage

main memorystoragememory
Every stored-program computer may use a form of non-volatile storage (that is, storage that retains its data when power is removed) to store the initial program that runs when the computer is powered on or otherwise begins execution (a process known as bootstrapping, often abbreviated to "booting" or "booting up"). Its designers explicitly broke from past practice, stating plainly that "the aim of NAND Flash is to replace hard disks," rather than the traditional use of ROM as a form of non-volatile primary storage.
Hence, non-volatile primary storage containing a small startup program (BIOS) is used to bootstrap the computer, that is, to read a larger program from non-volatile secondary storage to RAM and start to execute it. A non-volatile technology used for this purpose is called ROM, for read-only memory (the terminology may be somewhat confusing as most ROM types are also capable of random access).

Bit

binary digitbitsbinary digits
Consequently, ROM could be implemented at a lower cost-per-bit than RAM for many years.
In certain types of programmable logic arrays and read-only memory, a bit may be represented by the presence or absence of a conducting path at a certain point of a circuit.

IBM Monochrome Display Adapter

MDAMonochrome Display AdapterMonochrome Display Adapter (MDA)
This was the case for both the CGA and MDA adapters available with the IBM PC XT.
The character patterns are stored in ROM on the card and the character set cannot be changed from the hardware code page 437.

Microcode

microprogrammicroprogrammedmicroprogramming
Resistor, capacitor, or transformer matrix ROM, used in many computers until the 1970s. Like diode matrix ROM, it was programmed by placing components at selected locations between a matrix of word lines and bit lines. ENIAC's Function Tables were resistor matrix ROM, programmed by manually setting rotary switches. Various models of the IBM System/360 and complex peripheral devices stored their microcode in either capacitor (called BCROS for balanced capacitor read-only storage on the 360/50 and 360/65, or CCROS for charged capacitor read-only storage on the 360/30) or transformer (called TROS for transformer read-only storage on the 360/20, 360/40 and others) matrix ROM.
Engineers normally write the microcode during the design phase of a processor, storing it in a read-only memory (ROM) or programmable logic array (PLA) structure, or in a combination of both.