The state of a process

A process can be in a couple of states, each of them representing a certain point during the runtime of the process. The three main state are ready, running and blocked (there are a couple more depending on the operating system).

ready: The process was created and waits to be executed by the CPU.

running: The process has access to the CPU and is currently getting executed. This state can be interrupted and the access to the CPU be revoked.

blocked: The process is currently waiting on a resource. This can happen when waiting on the result of I/O operation. During this time the process has no access the CPU. When the resource arrives (I/O operation finishes) the process switches back into the ready state and can be picked up by the CPU again.