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Operating Systems

Ch. 14 - An Overview

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Architecture of Computer Hardware and Systems SoftwareIrv Englander, John Wiley, 2000

Bare Bones Computer System

Loading instructions into MM User interface Storing, retrieving, manipulating files Controlling peripheral devices

Does not provide for:

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Architecture of Computer Hardware and Systems SoftwareIrv Englander, John Wiley, 2000

SolutionProvide a set of programs that is an integral part of the computer system to:

Control the hardware Load and start application programs Provide file services Provide a user interface

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Architecture of Computer Hardware and Systems SoftwareIrv Englander, John Wiley, 2000

The Operating System is a collection of Programs that work together to act as a system manager, controlling both Hardware and Software and acting as a User Interface.

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Architecture of Computer Hardware and Systems SoftwareIrv Englander, John Wiley, 2000

Evolution of the Role of OS

Earlier systems required the user to know more about the hardware, file systems, and I/O devices to get work done, OS smaller

Trend is for the operating system to get bigger and provide more services so that the user has an easier time getting useful work done

The user is less likely to get bogged down with technical issues

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Architecture of Computer Hardware and Systems SoftwareIrv Englander, John Wiley, 2000

OS - Services Objectives

– Convenience– Efficiency

Services– Manage, load and execute programs– Accept and execute commands from user and application programs– Provide interface for user and user’s programs– Manage hardware resources

• I/O support• File support• Interrupt handling• Network services - such as, distributed processing• Concurrent Processing• Bootstrapping

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Architecture of Computer Hardware and Systems SoftwareIrv Englander, John Wiley, 2000

Bootstrapping

1. Execution begins with bootstrap loader stored in ROM

2. Looks for OS program in a fixed location

3. Loads OS into RAM

4. Transfers control to starting location of

OS

5. Loader program in OS used to load and

execute user programs

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Architecture of Computer Hardware and Systems SoftwareIrv Englander, John Wiley, 2000

OS Services

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Architecture of Computer Hardware and Systems SoftwareIrv Englander, John Wiley, 2000

OS Parts

Resident Part– some OS services are critical to system operation and

must be resident in memory at all times (user command handler, interrupt handler)

– loaded into memory via bootstrapping

– known as OS kernel

Non-Resident Part– loaded as needed, for example, disk formatting

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Architecture of Computer Hardware and Systems SoftwareIrv Englander, John Wiley, 2000

OS - Degree of Activity (between user and

system) Online, interactive (conversational system)

– user is connected directly to and interacting with system during execution of program (such as input)

Batch processing– program is executed in background mode

applied to data contained in a file Event driven

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Architecture of Computer Hardware and Systems SoftwareIrv Englander, John Wiley, 2000

Event Driven OS

An OS is usually idle until an event (interrupt or service request) occurs– File request– I/O request– Keyboard or mouse input– program memory request– clock interrupt signaling program scheduler for time

slice– etc

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Architecture of Computer Hardware and Systems SoftwareIrv Englander, John Wiley, 2000

Operating System - Types

Single User, Single Tasking

MSDOS Single User, Multitasking

Windows 95 or 98 Multi-user, Multitasking

Unix

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Architecture of Computer Hardware and Systems SoftwareIrv Englander, John Wiley, 2000

Single Job Processing

Simple Memory resident components

– Command interface shell containing commands that must remain resident

– I/O routines that control each of the I/O devices– File management system for locating and

maintaining files

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Architecture of Computer Hardware and Systems SoftwareIrv Englander, John Wiley, 2000

Single Job Processing 1. Program is loaded into memory.

2. Execution begins. Program runs w/o OS interference.

3. OS regains control:

a. If the user’s program requests I/O

b. The user wishes to stop the program execution via a keyboard interrupt

c. System malfunction

4. When program is finished, control is transferred back to the command interpreter. Note - computer does not halt. OS just waits for command.

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Architecture of Computer Hardware and Systems SoftwareIrv Englander, John Wiley, 2000

Single Job Processing

System provides minimum memory management and no scheduling

Wasteful of system resources - CPU is idle most of the time

Nearly obsolete

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Architecture of Computer Hardware and Systems SoftwareIrv Englander, John Wiley, 2000

Concurrent Operations

Multitasking - multiple programs running on a single CPU

May be applied to a single user system or to multiple users sharing a single system

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Architecture of Computer Hardware and Systems SoftwareIrv Englander, John Wiley, 2000

Allocates memory, CPU time, I/O devices to multiple programs

Protects users and programs from each other and provides for inter-program communication

Provides feedback to the system administrators for tailoring and tuning the system for optimum performance

Concurrent Processing

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Architecture of Computer Hardware and Systems SoftwareIrv Englander, John Wiley, 2000

OS ServicesConcurrent Operations

User services to each user Allocation of resources to each user and task

– Memory– I/O– CPU time

OS periodically evaluates status of resources and reassigns them in order to meet needs of each task and user

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Architecture of Computer Hardware and Systems SoftwareIrv Englander, John Wiley, 2000

Achieving Multitasking

1. While one program is waiting for I/O to take place, another program is using the CPU to execute instructions

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Architecture of Computer Hardware and Systems SoftwareIrv Englander, John Wiley, 2000

Sharing CPU during I/O Breaks

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Architecture of Computer Hardware and Systems SoftwareIrv Englander, John Wiley, 2000

Achieving Multitasking

2. The CPU may be switched rapidly back and forth between different programs

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Architecture of Computer Hardware and Systems SoftwareIrv Englander, John Wiley, 2000

Time-Slicing

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Architecture of Computer Hardware and Systems SoftwareIrv Englander, John Wiley, 2000

Achieving Multitasking

3. Concurrency algorithms usually combine both approaches, taking into account such issues as

- fairness to each program

- priorities of the programs

- quick response for critical needs, such as

displaying cursor or keystroke

- etc

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Architecture of Computer Hardware and Systems SoftwareIrv Englander, John Wiley, 2000

Concurrent OS Tasks Dispatching - selecting program to execute Keeping track of each program Memory management for each program I/O device scheduling to meet needs of each

program Suspending and restarting of all programs with

environment remaining intact Provide security and protection for all programs and

users

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Architecture of Computer Hardware and Systems SoftwareIrv Englander, John Wiley, 2000

Concurrent OS Tasks Control and measure performance of the

system establish and control communication

between programs Manage network communication ...

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Architecture of Computer Hardware and Systems SoftwareIrv Englander, John Wiley, 2000

OS - Structure User interface

– CLI - Command Line Interface– GUI - Graphical User Interface (menus,

icons, mouse-driven) I/O control system

– device drivers - programs for each device on the system, standard method for using each device

– Plug and Play - ideally to add new hardware and have the OS take care of adding it to all relevant programs and change settings to reflect change

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Architecture of Computer Hardware and Systems SoftwareIrv Englander, John Wiley, 2000

OS - Structure Process control management

– each executing program is a process

– each process acquires and releases resources during execution

– processes must be synchronized in order to facilitate sharing of resources

– OS provides process control management to keep track of each process and its status - executing, waiting for an event, register content, PC value, etc

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Architecture of Computer Hardware and Systems SoftwareIrv Englander, John Wiley, 2000

OS Structure

Memory Management– Each program is provided needed memory for

execution– For each program, OS keeps track of memory

allocated as well as free space, protects against writing outside allocated space, etc

– Maintains programs waiting to be loaded into memory and allocates/deallocates space on loading

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Architecture of Computer Hardware and Systems SoftwareIrv Englander, John Wiley, 2000

OS Structure

File Management– Mapping between a file’s logical name and the

physical address - maintains directories for each device

– Retrieval and storage of files– Info kept about each file

• (date, name, size, type, date last modified)

– Copy, move, delete, rename, find

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Architecture of Computer Hardware and Systems SoftwareIrv Englander, John Wiley, 2000

OS - Structure

Scheduling system– High level - jobs are placed in queue in some order and

ultimately loaded into memory for execution

– Dispatching - selection of process to be executed at a given point in time

• Mostly preemptive - that is, programs are multitasked based on time slicing

• Exception is for the OS itself in order to protect certain OS operations from being interrupted

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Architecture of Computer Hardware and Systems SoftwareIrv Englander, John Wiley, 2000

OS - Structure

Secondary storage management– Many processes may have simultaneous I/O requests

from secondary storage

– Processing of requests affect progress of processes to completion

– Secondary storage management reorganizes requests to optimize completion of I/O tasks (by minimizing track access)

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Architecture of Computer Hardware and Systems SoftwareIrv Englander, John Wiley, 2000

OS - Structure Security and protection management

– processes are limited to assigned memory space– file access is handled by OS

Support for system administration– configuring the system

• I/O device drivers, stack sizes, number of open files, ...

– adding/deleting users and passwords– providing backups– recovering lost data– installing/maintaining software– monitoring security and measuring performance