operating system in coa, Slides of Computer Architecture and Organization

Download operating system in coa and more Slides Computer Architecture and Organization in PDF only on Docsity!

Operating System Support

+ Objectives and Functions

• OS is a program that controls execution of application programs
• OS acts as an interface between the user of a computer and the

computer hardware.

Objectives

◼ Convenience - An OS makes a computer more convenient to use.

◼ Efficiency - An OS allows the computer system resources to be used in an efficient

manner.

◼ The most important system program

◼ Masks the details of the hardware from the programmer and

provides the programmer with a convenient interface for using the

system

+ Operating System Services

• Program creation - Editors, debuggers.
• Program execution - Tasks such as, Instructions and data load in main memory, I/O device and file initialization
• Access to I/O devices - OS hides details of specific set of instructions and control signals for every device. Programmer thinks in terms of simple read and write.
• Controlled access to files - Protection mechanism to control access to files in case of multi-users.
• System access - Protection of resources and data from unauthorized users
• Error detection and response - Operating system deals with errors in a way to minimize impact on running application. Response may be ending program that caused the error, or retrying the operation etc.
• Accounting - Usage statistics for various resources and monitor performance.

Operating System

as

Resource Manager

A computer is a set of resources for the movement, storage, and processing of data and for the control of these functions ◼ The OS is responsible for managing these resources The OS as a control mechanism is unusual in two respects: ◼ The OS functions in the same way as ordinary computer software – it is a program executed by the processor ◼ The OS frequently relinquishes control and must depend on the processor to allow it to regain control

+ Types of Operating Systems

◼ Interactive system

◼ The user/programmer interacts directly with the computer to request the execution of a job or to perform a transaction ◼ User may, depending on the nature of the application, communicate with the computer during the execution of the job

◼ Batch system

◼ Opposite of interactive ◼ The user’s program is batched together with programs from other users and submitted by a computer operator ◼ After the program is completed results are printed out for the user

+ Early Systems

◼ From the late 1940 s to the mid- 1950 s the

programmer interacted directly with the computer

hardware – there was no OS

◼ Processors were run from a console consisting of display lights, toggle switches, some form of input device and a printer

◼ Problems:

◼ Scheduling ◼ Sign-up sheets were used to reserve processor time ◼ This could result in wasted computer idle time if the user finished early ◼ If problems occurred the user could be forced to stop before resolving the problem ◼ Setup time ◼ A single program could involve ◼ Loading the compiler plus the source program into memory ◼ Saving the compiled program ◼ Loading and linking together the object program and common functions

+ Desirable Hardware Features ◼ Memory protection ◼ User program must not alter the memory area containing the monitor ◼ The processor hardware should detect an error and transfer control to the monitor ◼ The monitor aborts the job, prints an error message, and loads the next job ◼ Timer ◼ Used to prevent a job from monopolizing the system ◼ If the timer expires an interrupt occurs and control returns to monitor

◼ Privileged instructions

◼ Can only be executed by the monitor ◼ If the processor encounters such an instruction while executing a user program an error interrupt occurs ◼ I/O instructions are privileged so the monitor retains control of all I/O devices ◼ Interrupts ◼ Gives the OS more flexibility in relinquishing control to and regaining control from user programs

+ Multi-Programming with Two Programs

+ Multi-Programming with Three Programs

Uniprogramming Multiprogramming Processor use 20% 40% Memory use 33% 67% Disk use 33% 67% Printer use 33% 67% Elapsed time 30 min 15 min Throughput rate 6 jobs/hr 12 jobs/hr Mean response time 18 min 10 min Table 8. Effects of Multiprogramming on Resource Utilization

+ Time Sharing Systems

◼ Used when the user interacts directly with the computer

◼ Processor’s time is shared among multiple users

◼ Multiple users simultaneously access the system through

terminals, with the OS interleaving the execution of each user

program in a short burst or quantum of computation

◼ Example:

◼ If there are n users actively requesting service at one time, each user will only see on the average 1 / n of the effective computer speed

+ Process

Process: A program in execution

Process Control Block (PCB)

• Identifier
• State
• Priority
• Program counter
• Memory pointers
• Context data
• I/O status
• Accounting information

New Ready Blocked Running Exit

Figure 8.7 Five-State Process Model

Admit Dispatch Timeout Release Event Wait Event Occurs Five State Process Model