Thread control block

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Thread Control Block (TCB) is a data structure in an operating system kernel that contains thread-specific information needed to manage the thread.{{Cite web |date=2019-11-26 |title=Thread Control Block in Operating System |url=https://www.geeksforgeeks.org/thread-control-block-in-operating-system/ |access-date=2023-09-04 |website=GeeksforGeeks |language=en-us}} The TCB is "the manifestation of a thread in an operating system."

Each thread has a thread control block. An operating system keeps track of the thread control blocks in kernel memory.{{Cite web |title=CS162 - Fall 2014 #7 - Kernel Threads|url=https://inst.eecs.berkeley.edu/~cs162/fa14// |access-date=2023-12-07 |website=inst.eecs.berkeley.edu|archive-url=https://web.archive.org/web/20231207231258/https://inst.eecs.berkeley.edu/~cs162/fa14//|archive-date=2023-12-07|url-status=unfit}}

An example of information contained within a TCB is:

• Thread Identifier: Unique id (tid) is assigned to every new thread
• Stack pointer: Points to thread's stack in the process
• Program counter: Points to the current program instruction of the thread
• State of the thread (running, ready, waiting, start, done)
• Thread's register values
• Pointer to the Process control block (PCB) of the process that the thread lives on

The Thread Control Block acts as a library of information about the threads in a system. Specific information is stored in the thread control block highlighting important information about each process.