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Thread control block

Wikipedia contributorsAdapted for Fathomly · View authors
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Source updated October 25, 2025

Thread Control Block (TCB) is a data structure in an operating system kernel that contains thread-specific information needed to manage the thread. 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.

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.

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Sources and credits

This article is adapted from the Wikipedia article “Thread control block”, written by its contributors and licensed under CC BY-SA 4.0. Fathomly has changed the layout, removed citation markers, navigation and maintenance notices, and adjusted punctuation. This adapted version is shared under the same license. For references, see the original article.

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