What is memory ?

A CPU is just an operator on memory. It reads its instructions and data from the memory and writes back out to the memory. (Ward 2021)

When a CPU executes a program, it needs a place to store the program’s instructions and related data. This is the role of memory.

The data that comprises a program is a series of bits. The basic unit of memory storage is a memory cell: a circuit that can store a single bit.

RAM memory is volatile : the memory is only retained whilst the computer has a power supply and is wiped when the computer is rebooted. This contrasts with the memory of the harddisk which is non-volatile and is retained after a reboot.

Programs that are executing are loaded into memory because the chips that comprise memory can read and store data much faster than the harddisk. It would be possible to run a program from the harddisk but it would be 500 - 1000 times slower than memory.