Chap01-02-03

CECS 326

• Professor: Mr. Ratana Ngo• Textbook

• Title: Operating Systems, 3rd edition• Author: Gary Nutt• ISBN: 0-201-77344-9

• Assignments and Grading• Programs and homework packets: 25%• Quizzes and Exams: 50%• Final exam: 25%

Purpose and Benefits1. Sharing computing resources

2. Management of computing resources

• CPU, memory, other devices, and software

3. Speed of computation

4. Uniformity and portability• Hardware interface• Software interface

5. Mask system complexity

6. Internetworking

7. Protection, security, and reliability

Copyright © 2004 Pearson Education, Inc.

System Software

(revised) -- Operating Systems: A Modern Perspective, Chapter 1

LoaderLoader

OSOSDatabaseManagement

System

DatabaseManagement

System

WindowSystem

WindowSystem

ApplicationProgrammer

Syst

em S

oft w

are

LibrariesLibrariesCompilerCompiler

Hardware

CommandLine

Interpreter

CommandLine

Interpreter

LibrariesLibraries

Software APISoftware API


Sharing a CPU

• Efficiency: time multiplexing the CPU enables more than one application and more than one user to use the computer system

• Throughput: multiprogramming reduces the time to execute all computing tasks

• Responsiveness: multiprogramming minimizes computational delay

• Multi-tasking raises productivity• Multi-threading improves software


Time and space multiplexing

Using the processor

I/O operation

Time

Process 1

Process 2

Process 3

Process 4

Space-multiplexed Memory

Time-multiplexed CPU

Some considerationsCPU versus I/O (using rough estimates)

• CPU clock: 1 GHz (or 1 nsec/cycle)

• Keyboard: 100 wpm < 3000 char/min < 1 char/sec (or 1000 msec per char)

• Hard disk operation: 10 msec

Conclusion: I/O bound processes – User takes hundreds ofseconds to enter some data, CPU uses nanoseconds to process it. More than 90% of CPU capacity is wasted.

Question: Why are users obsessed with faster CPU?

Homework: Consider a DSL line at 1 Mbps! Estimate thedifference in speed. Where is the bottleneck?


Supporting multiprogramming

OS features needed for multiprogramming:

• Interface with input/output devices• Management of devices• Memory management• CPU scheduling


2

Using the operating system


Client-server example

(server)

loop forever

listen for client connection

spawn new child server

pass connection to child

endloop


The Shell Strategy

Shell ProcessShell Process

Processto executecommand

Processto executecommand

% grep first f3

f3

read keyboard fork a process

read file


OS Design Constraints

• Performance

• reliability

• Protection and security

• Correctness

• Maintainability

• Commercial factors

• Standards and open systems


Reliability

Hardware Resources

OS

OS Resources (OS Interface)

Middleware

Abstract Resources (API)

Application

User Interface

save

coutfwrite

write

print

layout view


Performance

• The OS is an overhead function ⇒ should not use too much of machine’s resources

• Minimum functionality is to implement generic services

• Additional function must be traded off against performance– DOS: single process– UNIX: command line interface and “stream of

bytes”


OS services• Program execution – system capability to load a

program and to run it• I/O operations – user programs are not allowed to

execute I/O operations directly; hence, the OS must provide some means to use I/O devices

• File system manipulation – program capability to read, write, create, and delete files

• Communications – exchange of information between processes executing either on the same computer or on different systems connected together by a network


OS services• Error detection – ensure correct computing by

detecting errors in the CPU and memory hardware, I/O devices, or in user programs

• Additionally:– Resource allocation – allocating resources to

multiple users or multiple jobs executing concurrently

– Accounting – keep track of and record which users use how much and what kinds of computer resources

– Protection – ensuring that all access to system resources is controlled


System calls

• A system call is an OS function provided by the operating system

• Applications use system calls to interface/request services from the OS

• Abstract all devices to a few interfaces: read, write, seek, ioctl, etc.

• Benefits: security, reliability, stability, uniformity/portability


System calls

• Process control – create, terminate, load, execute, allocate/deallocate memory, suspend, resume, etc.

• Device management – request, release, read, write, seek, mount/unmount, get/set attributes

• File management – create, delete, open, close, read, write, seek, get/set attributes

• Networking/communications – create/delete resources, send/receive data, attach/detach resources

• Information maintenance – get/set time/date, get/set system data, get/set process/file/device attribute, etc.


Common OS components

• Process management• Main memory management• Secondary management• File management• Device management• Networking/communications• Protection and security


Process management - overview

• A process is a program in execution. A process needs resources: CPU time, memory, files, I/O devices, etc. to complete its task.

• The OS is responsible for:– Process creation and deletion– Process suspension and resumption– Mechanism for

• Process synchronism• Process communication


Main memory management - overview

• Memory is a large array of bytes/words, each with its own address. It stores data shared by the CPU and I/O devices.

• Main memory is volatile.• The OS is responsible for:

– Keep track of which parts of memory are currently being used and by whom

– Decide which processes to load when memory space becomes available

– Allocate and deallocate memory space as needed


Secondary storage management - overview

• Since main memory is too small to accommodate all data and programs, the computer system provides secondary storage to back up main memory

• Modern computer systems use disks as primary on-line storage medium of data and programs

• The OS is responsible for:– Free space management– Storage allocation– Disk scheduling


File management - overview

• A file is a collection of related information defined by its creator. Commonly, files represent programs (both source and object forms) and data.

• The OS is responsible for:– File creation and deletion– Directory creation and deletion– Support of primitives for manipulating files and

directories– Mapping files onto secondary storage– File backup on stable storage media


Device management - overview

• The OS abstracts devices to a few common interfaces (see system calls)

• The I/O device system consists of:– Device allocation– Data buffering– Data caching– Device drivers


Networking/communications - overview

• A distributed system is a collection of processors that do not share memory or a clock.

• The computers in the system are connected through a communication network

• Communication takes place via a protocol• A distributed system provides users access to

various resources– Computational speed up– Increased data availability– Enhanced reliability


Protection and security - overview

• Protecting directory and file, CPU, I/O devices, memory, etc.

• Protection refers to a mechanism for controlling access by programs, processes, or users to both system and user resources

• The protection mechanism must:– Distinguish between authorized and unauthorized usage– Specify the controls to be imposed– Provide a means of enforcement

• Security policy defines strategies for sharing resources and is separate from mechanism


Basic Operating System Organization


Processor(s) Main Memory Devices

Process, Thread &Resource Manager

MemoryManager

DeviceManager

FileManager


CPU Modes

• Mode bit: Supervisor/monitor or User mode

• Supervisor mode– Can execute all machine instructions– Can reference all memory locations

• User mode– Can only execute a subset of instructions– Can only reference a subset of memory

locations


Kernels

• The critical part of the OS • trusted code that executes without any

constraints• essential that the kernel is correct• Executes in supervisor mode


LibrariesLibraries CommandsCommands

Device DriverDevice Driver

The UNIX ArchitectureInteractive User

ApplicationPrograms

ApplicationPrograms

OS System Call Interface



Dri

ver

Inte

rfac

eD

rive

r In

terf

ace

…Monolithic Kernel Module•Process Management•Memory Management•File Management•Device Mgmt Infrastructure

Trap Table

…


Linux architecture

• monolithic design to minimize the overhead of message passing• Linux kernel services include: CPU scheduling, process management,

memory management, interprocess communication

• loadable kernel modules can be loaded or unloaded as needed. these modules include file systems, device drivers, networking, etc.

• non-kernel OS services are implemented as system library functions


Microkernel Organization


Device managerDevice managerMicrokernelMicrokernel


LibrariesLibraries

ProcessProcess

ProcessProcess

ProcessProcess

File systemFile system SchedulerScheduler NetworkingNetworking

User

Supervisor


Windows NT Organization



LibrariesLibraries

ProcessProcess

ProcessProcess

ProcessProcess

SubsystemSubsystemUser

Supervisor

SubsystemSubsystem SubsystemSubsystem

Hardware Abstraction LayerHardware Abstraction LayerNT Kernel

NT ExecutiveI/O SubsystemI/O Subsystem

TT

TT

TT T T

T

Process ManagementMemory ManagementFile ManagementDevice Mgmt Infrastructure


Virtual Machines

• Each virtual machine is isolated from all other virtual machines • CPU scheduling can create the appearance that users have their

own processor• Spooling and a file system can provide virtual card readers and

virtual line printers

• A normal user time sharing terminal servers as the virtual machine operator’s console

Chap01-02-03

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