Processes

Programs are files passively stored on disk and contain binary code, which are machine language instructions that can run on the computer. Programs that are large and significant are referred to as applications.

Once the binary code of a program is copied to memory in order to start executing, we call such code a process.

• That is, a process is an instance of a program that is executing. A program can have several process instances (since you could run the same program several times simultaneously. E.g.: running 2 instances of the Calculator app on Windows simultaneously.)
• The notion of process also includes the memory sections associated with it, the files that it opens, the user who ran the program, and the threads that the process created. More on threads in the next topic.
• In batch systems, processes are referred to as jobs, and so both terms can be used interchangeably.

Every process has a unique identifier: its process ID (or pid.)