ROM

ROM (Read Only Memory) are computer chips inside of a computer which are inputed constant-datas, meaning that the computer can only read the data on these.

C64 ROM
The Commodore 64 had 20kb of ROM and 3 ROM chips: The BASIC ROM (8kb), the KERNAL (8kb) and the Character ROM (4kb).

EPROM
Another type of ROM is EPROM (Erasable Programmable Read Only Memory), which can be edited with a supplementary electric signal to update the firmware or the BIOS but if any errors occur during the update, the device will cease to work correctly.