Chapter 1: Introductioncse.snu.ac.kr/scsc/sites/default/files/운영체제의... · 2018. 8....

Silberschatz, Galvin and Gagne 2010 1.1

Chapter 1: Introduction

What Operating Systems Do

Computer-System Organization

Operating-System Structure and Operations

Process Management

Memory and Storage Management

Protection and Security

Distributed Systems

Special-Purpose Systems


Objectives

To provide a grand tour of the major operating systems

components

To provide coverage of basic computer system

organization

Silberschatz, Galvin and Gagne 2010 1.3 Operating System Concepts

What is an Operating System?

A program that acts as an intermediary between

a user and the computer hardware.

Operating system goals:

Execute user programs

Make solving user problems easier.

Make the computer system convenient to use.

Use hardware in an efficient manner.

“Performance”

Throughput --- jobs / sec. system oriented

Utilization --- % of time busy system oriented

Response time --- sec / job user oriented

user oriented index conflicts with system oriented indices

User

OS

HW

Other Programs

OS

Hardware


Computer System Components

1. Hardware –

provides basic computing resources

(CPU, memory, I/O devices, …).

2. Operating system –

controls and coordinates the use of the hardware among

the various application programs for the various users.

3. Applications programs –

define the ways in which the system resources are used

to solve the computing problems of the users

(compilers, database systems, games, business programs).

4. Users

(people, machines, other computers).

Other Programs

OS

Hardware


Abstract View of System Components

Other Programs

OS

Hardware


Operating System Definitions

Definition 1 -- Resource allocator

manages and allocates resources.

Definition 2 -- Control program

controls the execution of user programs and operations of

I/O devices

.

Definition 3 -- Kernel

one program running at all times

memory resident all the time

all else depend on this program.

Other Programs

OS

Hardware


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


Computer Startup

bootstrap program is loaded at power-up or reboot

Typically stored in ROM or EEPROM, generally known as

firmware

Initializates all aspects of system

Loads operating system kernel and starts execution


Computer-System Operation

I/O devices and the CPU can execute concurrently.

Each I/O device controller

is in charge of a particular device type. (control reg, status reg.)

has a local buffer. (data register)

CPU moves data from/to main memory to/from local buffers

I/O is from the device to local buffer.

Device controller informs CPU that it has finished its operation

by causing an interrupt.

memory


Interrupt

enable, disable Intr.

PC←PC+4

Interrupt request bit

Instr. fetch

Instr. decode

Execution

Read data

Write Back

PC ← address of

interrupt handler

Save register

CPU

I’m Done

Next I/O

Please

PC: Program Counter Register

main()

----------

----------

----------

do-I/O;

----------

----------

----------

----------

----------

----------

----------

Intrp_handler()

-----------------

-----------------

-----------------

-----------------

-----------------


PC←PC+4


Instr. fetch

Instr. decode

Execution

Read data

Write Back

PC ← address of

interrupt handler

Save register

CPU

Various

devices

PC: Program Counter Register

main()

----------

----------

----------

do-I/O;

----------

----------

----------

----------

----------

----------

----------

Intrp_handler()

-----------------

disk:-----------

-----------------

-----------------

mouse:--------

-----------------

-----------------

printer:---------

-----------------

-----------------


Interrupt Vector

INTerrupt

Request

(INTR)

PC←PC+4

Interrupt bit set?

Instr. fetch

Instr. decode

Execution

Memory

Write Back

NO

PC

Intrp_Vector[Dev Code]

Save register

YES

CPU

Device

Code

main()

----------

----------

----------

do-I/O();

----------

----------

----------

----------

----------

----------

----------

Intrp_tty()

-----------------

-----------------

-----------------

-----------------

-----------------

Intrp_disk()

-----------------

-----------------

-----------------

-----------------

-----------------

Intrp_mouse()

-----------------

-----------------

-----------------

-----------------

-----------------


Interrupt v.s. Trap(Exception)

enable, disable Intr.

PC←PC+4


Instr. fetch

Instr. decode

Execution

Read data

Write Back

PC ← address of

interrupt handler

Save register

CPU

Exception

illegal address

illegal opcode

divide by zero


Interrupts vs. Trap(exception)

Interrupt Exception

Cause: external to CPU Cause: CPU internal - while

executing current instruction

eg I/O devices, timer eg Programming error

Anomalous conditions

Current instruction completes Current instruction

may not complete

Asynchronous to clock Synchronous to clock


Common Functions of Interrupt handling

Interrupts transfer control to the interrupt service routine(ISR)

generally, through the interrupt vector, which contains the addresses

of all the service routines.

Interrupt architecture must save the address of the interrupted

instruction.

Incoming interrupts are disabled while another interrupt is being

processed to prevent a lost interrupt.

A trap is a software-generated interrupt caused either by an error or a

user request.

operating system is interrupt driven.

Device interrupt

code vector pointers

ISR

ISR

O S “2nd

Device Interrupts”

700


Interrupt Handling

1.The operating system preserves the state of the CPU

by storing registers and the program counter.

2. Determines which type of interrupt has occurred by:

polling or

vectored interrupt (HW provides code)

3. Separate segments of code determine what action

should be taken for each type of interrupt

(ISR: Interrupt Service Routine)

Device interrupt

code vector pointers

ISR

ISR

O S disk

network

mouse

1.17 Silberschatz, Galvin and Gagne © 2005 Operating System Concepts

Interrupt Timeline


Direct Memory Access (DMA)

Structure

High-speed I/O devices such as disks are

able to transmit information at close to memory speeds.

Device controller transfers blocks of data from buffer storage

directly to main memory without CPU intervention.

Instead of interrupting every byte interrupt once when the

whole has been moved

CPU

memory

device

CPU involves in every data word movement?

CPU (central CPU) is too expensive for every byte I/O

I/O does not need BIG CPU, many complex instructions

store data

inc address small specialized (I/O purpose) CPU

loop test

DMA


Computer System Architecture

Single-Processor system.

Multiprocessor system.

Increased throughput

Economy of scale

Increased reliability

Symmetric vs. Asymmetric multiprocessing

Multi-core chip

Clustered system

High availability


Operating System Structure

Multiprogramming needed for efficiency

Single user cannot keep CPU and I/O devices busy at all times

Multiprogramming organizes jobs (code and data) so CPU always has one to execute

A subset of total jobs in system is kept in memory

One job selected and run via job scheduling

When it has to wait (for I/O for example), OS switches to another job


Memory Layout for a Single User System

Monitor

I/O was slower than CPU

While I/O is in progress

CPU was idle

But CPU was expensive


Memory Layout for Multiprogrammed

System

CPU + Tape

CPU +

CPU

Network


OS Features Needed for Multiprogramming

I/O routine supplied by the system.

Memory management –

the system must allocate the memory to several jobs.

Size of allocation , …

CPU scheduling –

must choose among several jobs ready to run on CPU

Allocation of devices.


Time-Sharing Systems–Interactive Computing

(multi-user system)

CPU is multiplexed among several jobs (batch-gcc-batch-mail-…)

Users are given illusion that he is using the whole system(interactive).

when the operating system finishes the execution of one command,

OS asks next “control statement” from the user’s keyboard.

Eg ppt, word, ….

Telephone

bill

gcc

mail

Windows

UNIX

Linux


Operating System Structure

Timesharing (multitasking) is logical extension in which CPU switches jobs so frequently that users can interact with each job while it is running, creating interactive computing

Response time should be < 1 second

Each user has at least one program executing in memory process

If several jobs ready to run at the same time CPU scheduling

If processes don’t fit in memory, swapping moves them in and out to run

Virtual memory allows execution of processes not completely in memory


Operating-System Operations

Interrupt driven by hardware

Software error or request creates exception or trap

Division by zero, request for operating system service

Other process problems include infinite loop, processes modifying each other or the operating system


Operating-System Operations

Dual-mode operation allows OS to protect itself and other system components

User mode and kernel mode

Mode bit provided by hardware

Provides ability to distinguish when system is running user code or kernel code

Some instructions designated as privileged, only executable in kernel mode

System call changes mode to kernel, return from call resets it to user


Dual-Mode Operation

Sharing system resources requires operating system to ensure

that an incorrect program cannot cause other programs to

execute incorrectly.

Provide hardware support to differentiate between at least two

modes of operations.

1. User mode – execution done on behalf of a user.

2. Kernel mode (or monitor-supervisor-system mode)

– execution done on behalf of operating system.


Dual-Mode Operation (Cont.)

Mode bit added to computer hardware to indicate the

current mode: kernel (0) or user (1).

When an interrupt or fault occurs hardware switches

to kernel(or protection) mode.

Privileged instructions can be used only in kernel mode.

Kernel

(OS) user

Interrupt / fault

CPU sets this bit

OS sets to user mode


Mode Transition


I/O Protection

All I/O instructions are privileged instructions.

Must ensure that a user program could never gain control of the computer in monitor mode

Given the I/O instructions are privileged, how does the user

program perform I/O?

System call – user process requests I/O action to OS Usually takes the form of a trap to a specific location in the interrupt

vector.

Control passes through the interrupt vector to

a (trap or system call) service routine in the OS,

and the mode bit is set to monitor mode by interrupt HW.

The monitor verifies that the parameters are correct and legal, executes the I/O request,

and returns control to the instruction following the system call.


I/O – only by system call

My a.out (parameters)

chmodk

Kernel a.out

trap

user_mode Kernel read( ) checks permission first

sys call

system

call

invocation

“change mode to kernel” is privileged instrucion

and is not allowed in user mode

trap()

read()


Use of a System Call to Perform I/O

sys call

handler


CPU Protection

Timer – interrupts computer after specified period to

ensure operating system maintains control.

Timer to prevent infinite loop / process hogging resources

Timer is decremented every clock tick.

When timer reaches the value 0, an interrupt occurs.

Timer is commonly used to implement time sharing.

Timer is also used to compute the current time.

Load-timer is a privileged instruction.


Process Management

A process is a program in execution. It is a unit of work within the system.

Program is a passive entity,

process is an active entity. Process needs resources to accomplish its task

CPU, memory, I/O, files

Initialization data Process termination requires reclaim of any reusable

resources


Process Management

Single-threaded process has one program counter

Process executes instructions sequentially, one at a time, until completion

Multi-threaded process has one program counter per thread

Typically system has many processes, some user, some operating system running concurrently on one or more CPUs

Concurrency by multiplexing the CPUs among the processes / threads


Process Management Activities

The operating system is responsible for the following

activities in connection with process management:

Creating and deleting both user and system processes

Suspending and resuming processes

Providing mechanisms for process synchronization

Providing mechanisms for process communication

Providing mechanisms for deadlock handling


Memory Management

All data in memory before and after processing

All instructions in memory in order to execute

Memory management determines what is in memory

when

Optimizing CPU utilization and computer response to users

Memory management activities

Keeping track of which parts of memory are currently being

used and by whom

Deciding which processes (or parts thereof) and data to

move into and out of memory

Allocating and deallocating memory space as needed


Storage Management

OS provides uniform, logical view of information storage

Abstracts physical properties to logical storage unit - file

Each medium is controlled by device (i.e., disk drive, tape drive)

Varying properties include

– access speed,

– capacity,

– data-transfer rate,

– access method (sequential or random)


File System Management

File-System management

Files usually organized into directories

Access control on most systems to determine who can access what

OS activities include

Creating and deleting files and directories

Primitives to manipulate files and directories

Mapping files onto secondary storage

Backup files onto stable (non-volatile) storage media


Mass-Storage Management

Usually disks used to store data that does not fit in main

memory or data that must be kept for a “long” period of

time.

Proper management is of central importance

Entire speed of computer operation depends on disk

subsystem and its algorithms

OS activities

Free-space management

Storage allocation

Disk scheduling

Some storage need not be fast

Tertiary storage includes optical storage, magnetic tape

Still must be managed

Varies between WORM (write-once, read-many-times) and

RW (read-write)


Performance of Various Storage

Movement between levels of storage hierarchy can be

explicit or implicit


I/O Subsystem

One purpose of OS is to hide peculiarities of hardware

devices from the user

I/O subsystem responsible for

Memory management of I/O including

buffering (storing data temporarily while it is being

transferred),

caching (storing parts of data in faster storage for

performance),

spooling (the overlapping of output of one job with input

of other jobs)

General device-driver interface

Drivers for specific hardware devices



Protection – any mechanism for controlling access to resources defined by the OS

Security – defense of the system against internal and external attacks

Huge range, including denial-of-service, worms, viruses, identity theft, theft of service



Systems generally first distinguish among users, to determine who can do what

User identities (user IDs, security IDs) include name and associated number, one per user

User ID then associated with all files, processes of that user to determine access control

Group identifier (group ID) allows set of users to be defined and controls managed, then also associated with each process, file

Privilege escalation allows user to change to effective ID with more rights


Many CPU

Tightly Coupled Loosely Coupled

Bus

(share clock, memory)

Board, Room

Network

Campus, Building, City

Parallel

Processing Multi-

Processing

Distributed

Processing

Network

Operating

System

P

CPU

CPU

CPU

CPU

P CPU

CPU

CPU

CPU

P

P

P

User/Program network

aware

User/Program

Not aware

of network


Distributed Systems

Distribute the computation among several physical

processors.

Loosely coupled system –

each processor has its own local memory;

processors communicate with one another through various

communication lines,

such as high-speed buses or telephone lines.

Advantages of distributed systems.

Resources Sharing

illusion that there is only one OS

Computation speed up – load sharing

Reliability

Communications


Distributed Systems (cont)

Requires networking infrastructure.

Local area networks (LAN) or Wide area networks (WAN)

Network Operating System

Different from distributed system

Each node (processor + OS) is autonomous

Aware of network


Parallel Systems

Multiprocessor system: Many CPU’s in close communication.

Tightly coupled system –

processors share memory and a clock;

communication usually takes place through the shared memory.

Advantages of parallel system:

Increased throughput (# of jobs / second)

Economical

Increased reliability

graceful degradation

fail-soft systems (fault tolerance – fault avoidance)

Terminology fault -- flaw, defect, wrong action itself

error – result of fault


Parallel Systems (Cont.)

Symmetric multiprocessing (SMP)

Each processor runs identical copy of the operating system.

Many processes can run at once without performance

deterioration.

Most modern operating systems support SMP

Asymmetric multiprocessing

Each processor is assigned a specific task;

master processor:

schedules and allocates work to slave processors.

More common in extremely large systems


Real-Time Systems

Rigid response time requirement (milli-seconds or faster)

Eg: missile control, medical equipment control system.

sensor

system computer

control

Deadline -- either hard or soft real-time.

Hard realtime must - atomic power plant

Soft realtime best effort - MP3 player, …

eg Robot

Missle

Atomic power plant


Real-Time Systems (Cont.)

Hard real-time:

Secondary storage limited or absent

(disk access time is not predictable)

data stored in memory

OS has to be different

(other OS -- no response time guarantee)

general-purpose operating systems.

Timesharing Systems

Soft real-time

Limited utility in industrial control of robotics

Useful in some applications (multimedia, virtual reality) .


Handheld Systems

Personal Digital Assistants (PDAs)

Cellular telephones

Issues:

Limited memory

Small display screens

Limited power

Slow processors

Smartphone


Desktop (PC) Systems

Personal computers

computer system dedicated to a single user.

I/O devices

keyboards, mice, display screens, personal printer

(from old system’s card readers, shared line printers)

Goal change:

From Maximum hardware utilization

To User convenience and responsiveness (Single user).

Do not need protection (Single user system)

Among users

Among user and system (minimum system is in ROM)

Vulnerable to worm, virus, etc.

PC operating systems (Windows, MacOS, Linux)


Computing Environments

Traditional computer

Blurring over time

Office environment

PCs connected to a network, terminals attached to

mainframe or minicomputers providing batch and

timesharing

Now portals allowing networked and remote systems

access to same resources

Home networks

Used to be single system, then modems

Now firewalled, networked


Computing Environments (Cont.)

Client-Server Computing

Dumb terminals supplanted by smart PCs

Many systems now servers, responding to requests generated by clients

Compute-server provides an interface to client to request services (i.e. database)

File-server provides interface for clients to store and retrieve files


Peer-to-Peer Computing

Another model of distributed system

P2P does not distinguish clients and servers

Instead all nodes are considered peers

May each act as client, server or both

Node must join P2P network

Registers its service with central lookup service on

network, or

Broadcast request for service and respond to requests

for service via discovery protocol

Examples include Napster and Gnutella


Web-Based Computing

Web has become ubiquitous

PCs most prevalent devices

More devices becoming networked to allow web access

New category of devices to manage web traffic among

similar servers: load balancers

Use of operating systems like Windows 95, client-side,

have evolved into Linux and Windows XP, which can be

clients and servers

Cloud computing


IDC: Windows Server still rules the server roost

By Mary Jo Foley | June 3, 2010, 7:17am PDT

Q1 2010 units Windows 1,379,487 (75.3%) Unix 65,451 (3.6%) Linux 380,429 (20.8%)

Q4 2009 units

Windows 1,434,225 (73.9%) Unix 84,851 ( 4.4%) Linux 412,041 (21.2%)

Q1 2010 dollars Windows $5.1 billion (48.9%) Unix $2.3 billion (22.2%) Linux $1.7 billion (16.2%)

Q4 2009 dollars

Windows $5.4 billion (41.6%) Unix $3.9 billion (29.9%) Linux $1.9 billion (14.7%)

http://www.zdnet.com/search?q=mary+jo+foley


Desktop OS Market Share

Windows 92.05%

Mac 6.39%

Linux 1.26%

SUN OS 0.00%


Major OS Issues

structure: how is the OS organized?

sharing: how are resources shared across users?

naming: how are resources named (by users or programs)?

security: how is the integrity of the OS and its resources ensured?

protection: how is one user/program protected from another?

performance: how do we make it all go fast?

reliability: what happens if something goes wrong – hardware or software

extensibility: can we add new features?


Major OS Issues

communication: how do programs exchange information

concurrency: how are parallel activities created and controlled?

scale: what happens as demands or resources increase?

persistence: how do you make data last longer than program executions?

distribution: how do multiple computers interact with each other?

accounting: how do we keep track of resource usage, and charge for it?

Chapter 1: Introductioncse.snu.ac.kr/scsc/sites/default/files/운영체제의... · 2018. 8....

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