Miscellaneous Topics OS

Process/Task:

• The term ‘process’ was first used by the operating system designers of the MULTICS system in 1960s.
•  There are various definitions to explain the concept of process. Some of these are –
• A process is –
  • A running part of a program.
  • A program in execution.
  • An instance of a program in execution.
  • An asynchronous activity.
  • The dispatchable unit.
  • Unit of work individually schedulable by an operating system.
  • A process is the unit of work in a system.
• In general, a process needs certain resources such as CPU time, memory, files, I/O devices, etc., to accomplish its task. These resources are given/available to the process when it created.
• A program by itself is not a process rather it is a passive entity, while a process is an active entity.
• It is known that two processes may be associated with the same program but they are nevertheless considered two separate execution sequences.
• Process is collection of two types – System Process(those process that execute system code and related with OS) and User Process(those process that execute user code and related with user). Both of these processes can potentially execute concurrently as per need.
• Operating system keeps track of all the active processes and allocates system resources to them according to policies devised to meet design performance objectives.
• To meet process requirements OS must maintain many data structures efficiently.
• A single processor may be shared among several processes with some scheduling algorithm being used to determine when to stop work on one process and provide service to a different one.
• In multiprogramming systems, processes are performed really in a pseudo-parallelism as if each process has its own processor. In fact, there is only one processor but it switches back and forth from process to process.
• According to the use of processor in the programs, we may classify a program as: –
  • Processor- bound program: A program taking long processor/CPU bursts (execution instants).
  • I/O- bound program: A program taking short processor bursts called I/O burst.
• Operating systems provides some way to create all the processes needed. In UNIX, processes are created by the fork system call, which makes an identical copy of the calling process. In other systems, system calls exist to create a process, load its memory, and start it running.
• In general, processes possess a way to create other processes.
• Each process has one parent process, but zero, one, two, or more children processes.
• In process management, operating system does –
  • the creation and deletion of both user and system processes
  • the suspension or resumption of processes
  • the provision of mechanisms for process synchronization
  • the provision of mechanisms for deadlock handling
  • Controlling the progress of the process
  • Process Scheduling
  • Dispatching
  • Interrupt handling / Exceptional handling
  • Switching between the processes
  • Process synchronization
  • Interprocess communication support
  • Management of Process Control Blocks.
• A process at run time can be either –
  • Implicit Tasking/Process –
    • Implicit process means that processes are defined by the system.
    • It is commonly found in general purpose multiprogramming systems.
    • In this approach, each program submitted for execution is treated by the operating system as an independent process.
    • Processes created in this manner are usually transient in the sense that they are destroyed and disposed of by the system after each run.
  • Explicit Tasking/Process –
    • Explicit tasking means that programs explicitly define each process and some of its attributes.
    • To improve the performance, a single logical application is divided into various related explicit processes.
    • Explicit tasking is used in situations where high performance in desired system programs such as parts of the operating system and real time applications are common examples of programs defined processes.

Logical and Physical Memory Address Space

Logical Address :

• • Logical address refers to the address which is generated by the CPU before processing.

Physical Address :

• • Physical address refers to the address which is generated during the manufacturing of the memory unit.

Thrashing 

• Thrashing refers to an instance of high paging activity. 

Caching

• Caching is the processing of utilizing a region of fast memory for a limited data and providing it for quick process. 

Root partition

• Root partition is memory area where the operating system kernel is located.
• It contains potentially important system files that are mounted during boot time.

Command Line Interface

• A command line interface is a way to interact with operating system that allows the user to type in commands that can immediately provide results.
• The main problem with a command line interface is that normal users have not to be familiar with the commands, including the switches and parameters that come with it. This is a downside for people who are not fond of memorizing commands.