Processes and Threads
In computing, a process is the instance of a computer program that is being executed by one or many threads. It contains the program code and its activity. Depending on the operating system (OS), a process may be made up of multiple threads of execution that execute instructions concurrently[2]
In computer science, a thread of execution is the smallest sequence of programmed instructions that can be managed independently by a scheduler, which is typically a part of the operating system. The implementation of threads and processes differs between operating systems, but in most cases a thread is a component of a process.[3]
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Hands on tools[edit]
In general, we use the top command to view summary information about the running processes and threads (and much more). To see actual thread activity (blech) on an OS X system, type the sudo dtruss -ap pid (where PID is the process you want to investigate).
There are GUI tools where you can view this information, but you should use command line interface.