Read-Only Memory (Rom)
Read-only memory (ROM) is a semiconductor integrated circuit that functions as a computer device for the permanent storage of data and programming instructions. Once it is prerecorded at the time of manufacture the ROM can be read randomly but cannot be modified. A ROM memory device is made when a design company provides a semiconductor manufacturer with the instructions or data that is to be stored, and then the manufacturer makes the specified devices according to those specifications. Since making memory devices is an expensive procedure, ROM devices are almost always made in very large quantities. Before making ROM devices, experimental designs are created in small quantities using PROM (programmable read-only memory) or EPROM (erasable programmable read-only memory). The evolved definition of ROM has expanded to also include forms of memory that can be modified, but generally only under particular circumstances, so that, in general usage, ROM means any read-only device, including PROM and EPROM.
ROM is often compared to random-access memory (RAM), also called main memory. ROM is called non-volatile storage because it retains its contents even when the power is switched off. RAM, on the other hand, is called volatile because it (generally) does lose its contents under the same conditions.
ROM, informally called nonerasable storage, is often a small amount of memory used inside computers to hold programs for embedded systems (components of computers systems used without human intervention) since they usually have a fixed purpose. On computer motherboards, ROM is normally present in the form of an integrated circuit (commonly called a "chip") such as the computer BIOS chip.
The BIOS (basic input/output system) is the set of software control routines that tests hardware at startup, starts the operating system, and supports the transfer of data among hardware devices. This information is stored in ROM so that it can be executed when the computer is turned on. It is critical that the data within the BIOS remains fixed so that the computer starts ("boots up") exactly the same way each time it is turned on. For this reason, the ROM is used to maintain a consistency in the operating system of the computer. In addition, ROMs are used extensively as controllers in peripheral devices (such as printers, whose fonts are usually stored in ROMs) and other electronic devices. ROM is also used in many other applications. A major purpose of this technology is within video games where a cartridge uses many ROM chips in order to store all the information that is necessary for the running of the game. ROM does not only exist in the form of chips. Compact disks (CDs) are ROM, too. When computers are used in handheld instruments, household appliances, automobiles, and other such products, the program instructions for their routines are generally stored in ROM chips or some other non-volatile chip such as a PROM or EPROM.
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