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ROM, or Read Only Memory is found on a small computer chip, usually already attached to the motherboard.
Where RAM may have a capacity of 4 to 8 Gigabytes in most systems, ROM is much smaller at 4 – 8 Megabytes.
The reason for ROM being much smaller is down to the programs and data that it is designed to hold. ROM is responsible for holding the BIOS (Basic Input / Output System) and Boot Up program.
The Basic Input / Output system allows the computer system to run before an operating system is installed or loaded. It has a number of purposes including running the POST (Power On Self Test), prompting the Boot Up Program, and Hardware Security.
Boot Up Program
The Boot Up Program has a single function – that is to move the operating system from secondary storage into RAM. Because RAM is volatile, it is not practical to keep the operating system in the RAM when the system is powered down.