Introduction to Os

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IT 2203 : Operating Systems

Chapter 1: Introduction
What Operating Systems Do Computer-System Organization Computer-System Architecture Operating-System Structure Operating-System Operations Process Management Memory Management Storage Management Protection and Security Computing Environments Open-Source Operating Systems

Saminda Premaratne

What is an Operating System?
A program that acts as an intermediary between a user of a computer and the computer hardware Operating system goals: Execute user programs and make solving user problems easier Make the computer system convenient to use Use the computer hardware in an efficient manner Improve overall system reliability Provide isolation, security and protection among user programs.

Why should I study Operating Systems?

Computer System Structure
Computer system can be divided into four components Hardware – provides basic computing resources CPU, memory, I/O devices Operating system Controls and coordinates use of hardware among various applications and users Application programs – define the ways in which the system resources are used to solve the computing problems of the users Word processors, compilers, web browsers, database systems, video games Users People, machines, other computers

Four Components of a Computer System

Operating System Definition
OS is a resource allocator
Manages all resources Decides between conflicting requests for efficient and fair resource use

Operating System Definition (Cont)
No universally accepted definition “Everything a vendor ships when you order an operating system” is good approximation But varies wildly “The one program running at all times on the computer” is the kernel. Everything else is either a system program (ships with the operating system) or an application program

OS is a control program
Controls execution of programs to prevent errors and improper use of the computer

Goals of an Operating System
Simplify the execution of user programs and make solving user problems easier. Use computer hardware efficiently. Allow sharing of hardware and software resources. Make application software portable and versatile. Provide isolation, security and protection among user programs. Improve overall system reliability error confinement, fault tolerance, reconfiguration.

Bootstrap Loader
One of the CMOS settings is Boot Order Bootstrap loader checks all possible boot devices for a Master Boot Record (MBR), in the order configured by the user Once the MBR has been found, the BIOS turns the boot process over to the boot device.

Computer Startup
bootstrap program is loaded at power-up or reboot
Typically stored in ROM generally known as firmware (coded instructions that are stored permanently in read-only memory ) Initializes all aspects of system Loads operating system kernel and starts execution

Bootstrap process
The operating system itself is a program that needs to be loaded into the memory and be run. How is this dilemma solved? The solution is a two-stage process. A very small section of memory is made of ROM and holds a small program called the bootstrap program. When the computer is turned on, the CPU counter is set to the first instruction of this bootstrap program and executes the instructions in this program. When loading is done, the program counter is set to the first instruction of the operating system in RAM.

Computer System Organization
Computer-system operation One or more CPUs, device controllers connect through common bus providing access to shared memory Concurrent execution of CPUs and devices competing for memory cycles

Memory Cycle
Main memory is a read/write memory that allows data to be retrieved (read) and stored (written) in what is known as the memory cycle. The memory cycle includes reading the data out of memory and/or writing the data into memory, either by a read/write operation or by separate read and write operations. The memory cycle is based on fixed...
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