Operating System Overview 1

                                         Operating System

Today computer is associate with our daily life frequently.The computer nothing useful with out operating system.So we have to learn OS to maintain our computer.

WHAT IS OPERATING SYSTEM?

Operating system is a system software that act as an intermediary between user and hardware.It provides the platform to run application software and execute program by help of hardware.

OS is generally divided into two parts one is -SHELL another is KERNEL.SHELL is usually interact with the user  or application software.we write some program to shell (shell script).Those program or application is interpreted by the help of KERNEL and it convert to the corresponding machine code of the program and execute it by the help of hardware.So KERNEL is interact with hardware.

So one question is important kernel is software or hardware?The answer is obviously hardware because kernel is a part os which is a system software.so kernel can't be hardware.

                                              Process State

As a process executes, it  changes state. The state of a process is defined in part by the current activity of that process. Each process may be in following states:

• NEW - A process is said to be a new state if the process is being created.
• READY- A process is said to be a ready state if it is waiting to be assigned to a processor.
• RUNNING- A process is said to be a running state if it currently  have the CPU.
• BLOCK (WAITING)- A process is said to a block or waiting state if it is waiting for some event to happen.
• TERMINATED- A process is in terminated state if it has finish his execution. 

                       Process control Block   

 

Each process is represented in the operating system by a process control block (PCB).Mainly PCB content information of any process such  as:

• Process State: The current state of t he process.
• Program Counter:It holds the information of next instruction to be executed for this process.
• CPU register: The resister are mainly general purpose register, index register, accumulator, stack pointer etc.
• CPU scheduling algorithm:This information includes a process priority,pointers to scheduling queues and any other scheduling parameters.
• Memory management information: It include the information of base register, limit register,page table,segmented table depending of the memory system use by the os.
• Accounting information:The information of cpu time ,real time used,time limits,job no. etc.
• I/O status information: The information includes the list of I/O device allocate to this process ,a list of open files,and so an.