Following is a list of the things stored in main memory and some of its uses:

1. Programs, made up of millions of machine instructions, are stored in main memory. The currently running program is always stored in main memory.
2. Data being operated upon by the running program, both input and output data, are stored in main memory.
3. Data coming from input devices or going to output devices usually makes a stop in main memory.
4. In a modern multiprogrammed operating system, programs that are not currently running, but which are ready to run, are stored in main memory.