Read-only memory (ROM)
Read-only memory (ROM) is a type of non-volatile memory used in computers and various electronic devices that allows data to be read but not written to or modified by ordinary users. It is crucial for storing essential firmware such as the BIOS, which enables a computer to boot up and perform basic functions. ROM is commonly found in personal computers, calculators, video game systems, and other consumer electronics. There are several types of ROM, including mask ROM, programmable ROM (PROM), erasable programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), and flash ROM, each with unique characteristics regarding data storage and modification capabilities.
Historically, ROM has evolved from early forms like punch cards to modern integrated circuits, which are designed to retain data without needing power. Notably, while ROM is permanent and typically comes preprogrammed, some variations like PROM and EEPROM allow for limited reprogramming. ROM is contrasted with random access memory (RAM) and hard drives, which permit both reading and writing of data. Additionally, ROM can be distributed on formats like CD-ROMs, which store data on optical discs. Understanding ROM and its functionalities is essential for grasping how computers execute fundamental processes and operate various applications.
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Read-only memory (ROM)
Read-only memory (ROM) is a type of memory that only can be read—not written—by most computer systems. In a personal computer, ROM often is used to store the BIOS (basic input/output system). It also is used in calculators, video-game systems, and other consumer electronic devices. ROM often comes in integrated chips, which take several forms. Some are preprogrammed by manufactures and cannot be reprogrammed, while others are blank and must be programmed by the consumer. The various types of ROM include mask ROM, programmable ROM, erasable programmable ROM, electrically erasable programmable ROM, and flash ROM.
Background
ROM is a type of computer memory that only can be read, not written. ROM holds data permanently and cannot be modified. ROM has been in use since the earliest computers. Some of the first ROM was in the form of punch cards, which were pieces of thick paper inserted into a computer. A computer scientist punched out specific patterns on the cards, which the computer then read.
Punch cards held very little data. However, they were able to provide simple commands to otherwise automated machines. As with other forms of ROM, computers were unable to modify any of the instructions present on the punch card. Punch cards remained popular throughout the nineteenth century but declined throughout the twentieth century. Some voting machines still utilize punch card ROM. Punch cards were made obsolete by drum memory, which was the first common electronic computer memory. This was replaced by tube memory, which involved the use of an electrically charged tube.
Tube memory remembered information only as long as it was electrically charged. This made long-term file storage difficult. Many companies sought to develop a new style of memory to combat this challenge. In 1965, the electronics company Sylvania developed a computer chip that stored 256 bits of information. Computer chips are sets of electronic circuits carefully placed on a flat semiconductor. In most modern chips, the semiconductor is made of silicon. ROM, Sylvania's earliest chip, was programmed by scratching connections to diodes with specialized tools. This chip retained the information programmed on it regardless of whether it was electrically charged. This made it extremely valuable to computer technicians and computer users.
Overview
ROM is a type of computer memory that a computer can read but not write. Writing refers to the process of encoding new information onto a chip. In most scenarios, ROM comes preprogrammed. Most consumer-grade computers come with a small amount of ROM already installed. This programming allows the computer to perform basic tasks, such as booting up.
ROM is commonly contrasted with random access memory (RAM) and hard drives. These forms of memory allow the computer to both read and store information. RAM stores data for a short period and can be read and written quickly. Hard drives store data for longer periods. Data stored on hard drives are read and written at a much slower pace.
In addition to its use in personal computers, ROM is utilized in other computerized devices. For example, ROM chips allow many consumer-grade calculators to perform their calculations. ROM also is commonly used in video games. Video-game manufacturers can distribute large numbers of games, encoded on ROM chips, to consumers. These chips require no programming on behalf of the consumer. Consumers are able to plug the cartridge containing the ROM chips into their specialized console and begin playing the game. Because consumers cannot easily modify the data contained on ROM chips, they are unable to modify the game's programming.
Other types of ROM can be distributed on compact discs (CDs). In this case, a CD containing important data is inserted into the optical drive of a computer. The computer uses a laser to read the data and then translates that data for the computer user as the disk spins. This format is commonly called a CD-ROM. CD-ROMs store a limited amount of information. They are delicate and easy to damage in transport or regular use.
In addition to CD-ROMs, ROM can come in numerous types of chips and circuits. Mask ROM, or MROM, comes programmed into a larger integrated circuit. It is commonly utilized by large network and server operating systems. Programmable ROM chips, often called PROM, are distributed blank from the manufacturer. The purchaser must use specialized PROM programmers or PROM burners to write code to the chip. Once code is written to the PROM, it can never be modified.
Computer engineers sometimes need to reprogram ROM chips with different coding. For this reason, they invented erasable programmable ROM, or EPROM. Unlike PROM chips that cannot be modified, EPROM chips can be erased. Ultraviolet rays can travel through a window on the chip, which erases the data it contained and allows computer engineers to reprogram it.
Some erasable ROM chips can be cleared without the use of ultraviolet rays. Instead, the erasing is conducted with an electric current. These chips, called electrically erasable programmable ROM (EEPROM) chips, can be cleared and reprogrammed from inside a computer. Additionally, EEPROM chips allow computer engineers to erase and reprogram a small part of a chip rather than erasing and reprogramming its entire contents.
Flash ROM serves a similar purpose to EEPROM chips. However, flash ROM uses flash memory technology. This allows computer engineers to alter several memory locations at the same time. It was named for its ability to delete large sections of data in a short time.
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