The architecture of computer hardware and systems software an information technology approach ch15p1

Chapter 15The Internal Operating System – Part 1 15.1-4 Network Services File management Device management / Resource allocation Memory management / Scheduling Monitor IOCS I/O control

Chapter 15 – Part 1

The Internal Operating System

The Architecture of Computer Hardware

and Systems Software:

An Information Technology Approach

3rd Edition, Irv Englander John Wiley and Sons 2003

Target Model

Chapter 15

The Internal Operating System – Part 1 15.1-4

Network Services File management

Device management / Resource allocation

Memory management / Scheduling

Monitor

IOCS (I/O control system)

Translates logical file

requests

Load programs into MM

Allocates execution time

Provides overall system

control

Loading and Executing a Program

Multi-Tasking System

memory, I/O) to multiple processes

 Different scheduling routines are used for different objectives

Chapter 15

The Internal Operating System – Part 1 15.1-6

Processes

 Process: basic unit of work in the OS

 A program together with all the resources that are associated with it as it is executed

 Program: a file or listing

 Process: a program being executed

 Independent vs cooperating processes

 PID (process ID): a unique identifier for each process

 Process creation: user vs system

 Forking, spawning, cloning a new process

 Parent and child processes

Process Control Block

 A block of data for

each process in the

system

 Contains all relevant

information about the

process

 Typical process

control block on the

right 

Chapter 15

The Internal Operating System – Part 1 15.1-8

Two Processes Sharing a

Single Program

 Dispatching - Move from ready state to running state

 Wake-up - Move from blocked state to ready state

 Time-out - Move from running state to ready state

 Process completion

 Additional states – suspend, swap

 Resumption – Move from suspended state to ready state

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The Internal Operating System – Part 1 15.1-10

Process State Diagram

 Advantage of process/thread families over

multiple independent processes:

 Reduced OS overhead for resource allocation and process management

 Substantially less information than a normal PCB

(dispatcher)

Deciding which process shall be executed next by the processor Mid-level scheduling Swapping processes

I/O scheduling Deciding which process’s pending

I/O request shall be handled by an available I/O device

Dispatching Objectives

response time

 Prevent starvation

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The Internal Operating System – Part 1 15.1-14

Nonpreemptive Dispatching

 First in, first out (FIFO)

 Unfair to short processes and I/O based

processes

 Shortest Job First (SJF)

 Longer jobs can be starved

 Priority Scheduling

 Dispatcher selects among jobs with the

same priorities

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The Internal Operating System – Part 1 15.1-16

Preemptive Dispatching

 Multilevel feedback queues

 Favors short jobs, I/O bound jobs

 Each level assigns more CPU time

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The Internal Operating System – Part 1 15.1-18

Memory Overlays

Virtual Memory

 Virtual memory increases the apparent

amount of memory by using far less

expensive hard disk space

 Provides for process separation

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The Internal Operating System – Part 1 15.1-20

Frames and Pages

Amount # of bits in instruction word Installed memory

Frames and Pages

Binary Paging

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The Internal Operating System – Part 1 15.1-22

Dynamic Address Translation

Disk

Page Frame

Pages not in main memory:

page fault when accessed

10 1 2 7

Page Table

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The Internal Operating System – Part 1 15.1-26

Page Replacement Algorithms

 Page fault - page is not in memory and must

be loaded from disk

 Algorithms to manage swapping

 First-In, First-Out FIFO – Belady’s Anomaly

 Least Recently Used LRU

 Least Frequently Used LFU

 Not Used Recently NUR

 Second Chance Replacement algorithms

 Thrashing

 too many page faults affect system performance

Virtual Memory Tradeoffs

Disadvantages

 SWAP file takes up space on disk

 Paging takes up resources of the CPU

Advantages

 Programs share memory space

 More programs run at the same time

 Programs run even if they cannot fit into

memory all at once

 Process separation

Chapter 15

The Internal Operating System – Part 1 15.1-28

Virtual Memory vs Caching

Secondary Storage Scheduling

 First-Come, First-Served

 Shortest Distance First

 Indefinite postponement problem

 Scan

 Middle of disk gets serviced twice

 N-Step C-Scan

 Disk seek in only one direction

 Return after last request in queue served

 Two queues

Chapter 15

The Internal Operating System – Part 1 15.1-30

Other OS Issues

 Two processes have one another’s

resources that the other needs in order to proceed

 Prevention

 Avoidance

 Detection and recovery

Java Virtual Machine