What do most computers use to hold their startup intructions because it allows the computer easily to update its contents?

Answer 1

Computers are started by the BIOS (Basic Input/Output System) passing instructions to the CPU to load the operating system.

This is usually stored on a Flash memory chip on the motherboard, but sometimes the chip is another type of ROM. Flash memory is a type of EEPROM chip, which stands for Electronically Erasable Programmable Read Only Memory.

Traditionally ROM chips were hardware and as such were read only, hence the name ROM (Read Only Memory). Some chips are able to be re-written, however, and this is what happens if/when you update your computer's BIOS. A newer version of the instructions can be loaded onto the Flash memory chip and stored semi-permanently on the chip, which means permanently unless/until such time as it is overwritten again.