A process is a running instance of a program, with its own memory and resources. Launching the same program twice creates two processes that cannot see each other's memory.
The OS tracks each process in a structure often called a process control block. It records the process ID, current registers, the program counter, and memory layout. It also holds open file descriptors, the parent process, scheduling priority, and current state like running, ready, or waiting.
This bookkeeping is what makes pausing and resuming possible. When the OS switches away, it saves those registers, then restores them later so the process continues exactly where it stopped. The tracked state is the process's whole identity to the kernel.
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