1. Process Control Block (PCB)
What is the PCB?
A data structure used by an operating system to manage processes
Also called a task control block
Makes multiprogramming possible
Patent was filed in 1974 and received in April 1978

2. Process Control Block
First computer systems processed a single process at a time
Earliest digital computers had no operating systems. Programs were entered one bit at time on mechanical switches.
The General Motors Research Laboratories implemented the first operating systems in early 1950's for their IBM 701.
Ran one job at a time
Called single-stream batch processing systems because programs and data were submitted in groups or batches.
Need to use the resources more efficiently
“Operating systems designers developed the concept of multiprogramming in which several jobs are in main memory at once; a processor is switched from job to job as needed to keep several jobs advancing while keeping the peripheral devices in use.”
History of Operating Systems

3. Process Control Block (PCB)
Inventors:
Marc Appell, Paris, France
John J. Bradley, Garches, France
Benjamin S. Franklin, Cambridge, Mass

4. Process Control Block (PCB)
Process States
The Queues
Each state queue has a list of PCBs
List contains the address (pointers) of the PCBs
A new PCB is created at the New State and kept till the process is terminated
When a process is moved from one state to another it’s corresponding PCB record pointer is moved from one state list to another state list Q Q Q Q

5. What does the PCB contain?
Pid (Process ID)
The identifier the O/S give the process
Process State
new, ready, waiting, running, terminated
Register content
Pointers to the locations in the program and its data where processing last occurred. (when leaving the run state the registers in the CPU are copied over to the PCB)
Pointer to memory
upper and lower bounds of memory required for the process
Other data in the PCB
States of Various flags and switches
A list of files opened by the process
The priority of the process
Status of all I/O devices needed by the process
Parent process / child process

6. Resources