A UNIX process is created by the operating system. It typically contains the following:

• A process ID, process group ID, user ID, or group ID
• An environment and working directory
• Program instructions
• Registers, a stack, and a heap
• File descriptors
• Signal actions
• Shared libraries
• Inter-process communication tools (pipes, message queues, semaphores, or shared memory)

If you are curious about processes, open up a shell and type $ top. This command displays and updates sorted information about the processes that are running in your system. When I run it on my machine, the first line tells me the following:

$ top
Processes: 477 total, 4 running, 473 sleeping, 2234 threads
...

This gives you an idea about how much work our computers are doing without us being really aware of it.