Process control block


Process control block

A Process Control Block (PCB, also called Task Control Block or Task Struct) is a data structure in the operating system kernel containing the information needed to manage a particular process. The PCB is "the manifestation of a process in an operating system". [cite book |last=Deitel |first=Harvey M. |title=An introduction to operating systems |origyear=1982 |url=http://portal.acm.org/citation.cfm?id=79046&dl=GUIDE&coll=GUIDE |edition=revisited first edition |year=1984 |publisher=Addison-Wesley |id=ISBN 0-201-14502-2 |pages=673 pages 57-58]

Included information

Implementations differ, but in general a PCB will include, directly or indirectly:

* The identifier of the process (a process identifier, or PID)
* Register values for the process including, notably,
*: the Program Counter value for the process
* The address space for the process
* Priority
* Process accounting information, such as when the process was last run, how much CPU time it has accumulated, etc.
* Pointer to the next PCB i.e. pointer to the PCB of the next process to run
* I/O Information (i.e. I/O devices allocated to this process, list of opened files, etc)

During a context switch, the running process is stopped and another process is given a chance to run. The kernel must stop the execution of the running process, copy out the values in hardware registers to its PCB, and update the hardware registers with the values from the PCB of the new process.

Location of the PCB

Since the PCB contains the critical information for the process, it must be kept in an area of memory protected from normal user access. In some operating systems the PCB is placed in the beginning of the kernel stack of the process since that is a convenient protected location. [Yong, Zhang, "Breaking through the Maximum Process Number", "Linux Journal", 1 Jan 2004, [http://www.linuxjournal.com/article/4407] .]

Notes


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Process Control Block — Die Prozesstabelle ist ein Begriff aus der Informatik. Es handelt sich dabei um eine Tabelle, die pro laufendem Prozess einen Eintrag enthält. Diesen Eintrag nennt man Prozesskontrollblock (Prozesskontext, engl. process control block, task… …   Deutsch Wikipedia

  • Process Control Block — En informatique, un bloc de contrôle de processus ou PCB (de l anglais Process Control Block) est une structure de données du noyau d un système d exploitation représentant l état d un processus donné. Diverses implémentations existent selon les… …   Wikipédia en Français

  • Process management (computing) — Operating systems …   Wikipedia

  • Process (computing) — In computing, a process is an instance of a computer program that is being executed. It contains the program code and its current activity. Depending on the operating system (OS), a process may be made up of multiple threads of execution that… …   Wikipedia

  • Process and instrumentation diagram — Process and instrumentation diagrams are a family of functional one line diagrams showing hull, mechanical and electrical (HM E) systems like piping, and cable block diagrams. Abbreviated as P ID, they show the interconnection of process… …   Wikipedia

  • Process design (chemical engineering) — Process design is the design of processes for desired physical and/or chemical transformation of materials. Process design is central to chemical engineering and it can be considered to be the summit of chemical engineering, bringing together all …   Wikipedia

  • Control theory — For control theory in psychology and sociology, see control theory (sociology) and Perceptual Control Theory. The concept of the feedback loop to control the dynamic behavior of the system: this is negative feedback, because the sensed value is… …   Wikipedia

  • Control flow diagram — Example of a so called performance seeking control flow diagram .[1] A control flow diagram (CFD) is a diagram to describe the control flow of a business process, process or program. Contr …   Wikipedia

  • Process flow diagram — A process flow diagram (PFD) is a diagram commonly used in chemical and process engineering to indicate the general flow of plant processes and equipment. The PFD displays the relationship between major equipment of a plant facility and does not… …   Wikipedia

  • Control flow graph — Simplified control flowgraphs[1] A control flow graph (CFG) in computer science is a representation, using graph notation, of all paths that might be traversed through a program during its execution …   Wikipedia


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.