The document discusses the process control block (PCB), which contains key information needed by the operating system to manage processes. The PCB includes process identification data like the process ID, process state data like CPU register values, and process control data like scheduling information. It stores information needed for tasks like context switching between processes. PCBs allow the OS to track processes and resources like memory and devices allocated to each process. They are located in protected memory areas like the kernel stack.

1. PROCESS CONTROL BLOCK

2. Introduction :
• It is a data structure in the OS kernel containing the information
needed to manage the scheduling of a particular process.
• Other names:
Task Controlling Block, Entry of the Process Table, Task Struct, or Switchframe.
• The PCB is "the manifestation of a process in an operating system."

3. Role :
• The role of the PCBs is central in process management:
• Accessed and/or modified by most OS utilities, including those involved with
scheduling, memory and I/O resource access and performance monitoring.
• The set of the PCBs :
• defines the current state of the operating system.
• Data structuring for processes is often done in terms of PCBs.
• For example, pointers to other PCBs inside a PCB allow the creation of
those queues of processes in various scheduling states("ready",
"blocked", etc.).

4. Structure :
• In modern multitasking systems,
• PCB stores :
1. Process identification data
2. Process state data
3. Process control data

5. • Process identification :
• data always include a unique identifier for the process
• in a multiuser-multitasking system, data like the identifier of the parent process, user
identifier, user group identifier, etc. The process id is particularly relevant, since it is
often used to cross-reference the OS tables defined above, e.g. allowing to identify
which process is using which I/O devices, or memory areas.
• Process state :
• data define the status of a process when it is suspended, allowing the OS to restart it
later and still execute correctly.
• Includes the content of the CPU general-purpose registers, the CPU process status
word, stack and frame pointers etc. During 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.

6. • Process control information :
• Is used by the OS to manage the process itself.
• This includes:
1. The process scheduling state: The state of the process in terms of "ready",
"suspended", etc., and other scheduling information as well, like priority value,
the amount of time elapsed since the process gained control of the CPU or
since it was suspended. Also, in case of a suspended process, event
identification data must be recorded for the event the process is waiting for.
2. Process structuring information: process's children id's, or the id's of other
processes related to the current one in some functional way, which may be
represented as a queue, a ring or other data structures.
3. Interprocess communication information: various flags, signals and messages
associated with the communication among independent processes may be
stored in the PCB.
4. Process Privileges in terms of allowed/disallowed access to system resources.

7. PCB :

8. • Process State: State may enter into new, ready, running, waiting, dead depending
on CPU scheduling.
• Process Number (PID): A unique identification number for each process in the
operating system (also known as Process ID).
• Program Counter (PC): A pointer to the address of the next instruction to be
executed for this process.
• CPU Registers: Indicates various register set of CPU where process need to be
stored for execution for running state.
• CPU Scheduling Information: indicates the information of a process with which it
uses the CPU time through scheduling.
• Memory Management Information: includes the information of page table,
memory limits, Segment table depending on memory used by the operating
system.
• Accounting Information: Includes the amount of CPU used for process execution,
time limits, execution ID etc.
• I/O Status Information: Includes a list of I/O devices allocated to the process.

9. Location :
• Since 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 as it is a convenient protected location
• Kernel stack

10. Thank You