Why Does a Microprocessor Contain ROM Chips?

ROM versus RAM

A ROM chip can store a predetermined amount of data. As an example, it is common for microprocessors to contain 128 bytes of memory, but some can contain more or less. All information stored in ROM can be retrieved after the computer shuts down. On the other hand, information stored on RAM chips are not permanent, meaning that they disappear once the computer shuts off. As a result, all computers need ROM to save data permanently.

In a personal computer, the ROM chips are commonly known as the BIOS (basic input/output system). The BIOS holds instructions for the computer to complete once it's powered on. As soon as the user presses the power button, the microprocessor begins executing instructions it finds in the BIOS. Also, the BIOS usually holds information such as the computer's internal clock. In order to store that information accurately, the BIOS requires a 3-volt battery used commonly in watches. Without the battery, the system clock needs to be reset every time a user restarts his computer.

ROM is also responsible for directing the microprocessor toward the boot sector of the computer's hard drive. The hard drive is where most users' data are stored. The boot sector is a special section of the hard drive that holds instructions for the microprocessor to execute when powering on. These instructions tell the microprocessor where to find the operating system, software like Microsoft Windows, Mac OSX or Linux.

Upon boot-up, ROM is responsible for instructing the computer to test its hardware. When a computer starts up, it must check all of its hardware components, including hard drive, CD-ROM drive, keyboard, mouse, monitor, graphics cards, sound cards and network cards. This hardware test ensures that everything is working properly. When computer technicians need to diagnose a computer problem, one strategy relies on the hardware tests run by the ROM chip on the microprocessor.