ENVS 1800 Lecture Notes - Lecture 7: Process Control Block, Program Counter, Minos
14 May 2018
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ENVS 1800 Lecture 7 Notes – Process Creation
Introduction
• Active processes are readily observable on the Linux system using the ps command.
• Next, the PCB contains pointers to other, related processes.
• This issue is related to the way in which new processes are created. It is discussed
• The presence of this area simplifies communication between related processes.
• Following the pointer area is an indicator of the process state.
• In MINOS, four process states were possible: inactive, ready, blocked, and running.
• In larger systems, there are other possible states; processor states are discussed later in
this section.
• The program counter and register save areas in the process control block are used to
save and restore the exact context of the CPU when the process gives up and regains
the CPU.
• Memory limits establish the legal areas of memory that the process may access.
• The presence of this data simplifies the task of security for the operating system.
• Similarly, priority and accounting information is used by the operating system for
scheduling and for billing purposes.
• Finally, the process control block often contains pointers to shared program code and
data, open files, and other resources that the process uses.
• This simplifies the tasks of the I/O and file management systems.
• A little thought should make it clear to you that a process is created when you issue a
command that requests execution of a program
• Either by double-clicking on an icon or by typing an appropriate command
• There are also many other ways in which a process is created.
• Particularly on interactive systems, process creation is one of the fundamental tasks
performed by the operating system.
• Processes in a computer system are continually being created and destroyed.
• The PCB contains pointers to other, related processes.
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