Operating System Concepts

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Operating System Concepts

Tei-Wei Kuo

ktw@csie.ntu.edu.tw

Dept. of Computer Science and Information Engineering

National Taiwan University

Syllabus

授課教授: 郭大維 @ Room 315.資工系. NTU.TW

助教: 陳雅淑 (yashc@mail2000.com.tw) 張原豪 (d93944006@ntu.edu.tw )

上課時間: Wednesday 14:20-17:20

教室:資 103

教科書：

Silberschatz, Galvin, and Gagne, “Operating System Principles,” 7th Edition, John Wiley

& Sons, Inc..

成績評量：(subject to changes.):

期中考(40%), 期末考(40%), 作業(20%)

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Projects – Nachos 4.0

Not Another Completely Heuristic Operating System

Written by Tom Anderson and his students at UC Berkeley

http://www.cs.washington.edu/homes/tom/nachos/

It simulates an MIPS architecture on host systems

(Unix/Linux/Windows/MacOS X)

User programs need a cross-compiler (target MIPS)

Nachos appears as a single threaded process to the host operating system.

Chapter 1. Introduction

Introduction

What is an Operating System?

A basis for application programs

An intermediary between users and hardware

Amazing variety

Mainframe, personal computer (PC), handheld computer, embedded

computer without any user view Convenient vs Efficient

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Computer System Components

OS – a government/environment provider

Application Programs Operating System

Hardware

User User ... User

CPU, I/O devices, memory, etc.

compilers,

word processors, spreadsheets, browsers, etc.

User View

The user view of the computer varies by the interface being used!

Examples:

Personal Computer Æ Ease of use

Mainframe or minicomputer Æ

maximization of resource utilization

Efficiency and fair share

Workstations Æ compromise between individual usability & resource utilization

Handheld computer Æ individual usability

Embedded computer without user view Æ run without user intervention

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System View

A Resource Allocator

CPU time, Memory Space, File

Storage, I/O Devices, Shared Code, Data Structures, and more

A Control Program

Control execution of user programs

Prevent errors and misuse

OS definitions – US Dept.of Justice against Microsoft in 1998

The stuff shipped by vendors as an OS

Run at all time

System Goals

Two Conflicting Goals:

Convenient for the user!

Efficient operation of the computer system!

We should

recognize the influences of operating systems and computer architecture on each other

and learn why and how OS’s are by

tracing their evolution and predicting what they will become!

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UNIX Architecture

terminal controller, terminals,

physical memory, device controller, devices such as disks, memory, etc.

CPU scheduling, signal handling, virtual memory, paging, swapping,

file system, disk drivers, caching/buffering, etc.

Shells, compilers, X, application programs, etc.

UNIX Kernel interface

to the hardware System call interface

useruser user useruser user User user

interface

Computer-System Structure

Objective: General knowledge of the structure of a computer system.

printer CPU

printer controller

memory controller

disk controller

memory

tape-drive controller

disks

tape drivers

Device controllers: synchronize and manage access to devices.

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Booting

Bootstrap program:

Initialize all aspects of the system, e.g., CPU registers, device

controllers, memory, etc.

Load and run the OS

Operating system: run init to initialize system processes, e.g., various

daemons, login processes, after the kernel has been bootstrapped.

(/etc/rc* & init or /sbin/rc* & init)

Interrupt

Hardware interrupt, e.g. services requests of I/O devices

Software interrupt, e.g. signals, invalid memory access, division by zero, system calls, etc – (trap)

Procedures: generic handler or interrupt vector (MS-DOS,UNIX)

process execution

interrupt

handler return

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Interrupt Handling Procedure

Saving of the address of the interrupted instruction: fixed locations or stacks

Interrupt disabling or enabling issues: lost interrupt?!

prioritized interrupts Æ masking

interrupted process

system stack fixed address

per interrupt type

interrupted address, registers ...

handler

Interrupt Handling Procedure

Interrupt Handling

Î Save interrupt information

Î OS determine the interrupt type (by polling) Î Call the corresponding handlers

Î Return to the interrupted job by the restoring important information (e.g., saved return addr. Æ program counter)

indexed by a unique

device number

Interrupt Vector

0 1

n

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

--- ---

--- --- ---

Interrupt Handlers (Interrupt Service Routines)

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Storage Structure

Access time: a cycle

Access time:

several cycles

Access time: many cycles

memory

Magnetic Disks registers

cache

CD-ROMs/DVDs

Jukeboxes Tertiary Storage

• removable media

Secondary Storage

• nonvolatile storage

HW-Managed

SW-Managed

Primary Storage

• volatile storage

CPU

* Differences:

Size, Cost,

Speed, Volatility

Memory

Processor can have direct access!

Intermediate storage for data in the registers of device controllers

Memory-Mapped I/O (PC & Mac) (1) Frequently used devices

(2) Devices must be fast, such as video controller, or special I/O instructions is used to move data between

memory & device controller registers

Programmed I/O – polling

or interrupt-driven handling

R1 R2

R3 . . .

Memory

Device Controller

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Magnetic disks

Transfer Rate

Random- Access Time

Seek time in x ms

Rotational latency in y ms

60~200 times/sec spindle

sector

cylinder

platter

r/w head

disk arm arm assembly track

Magnetic Disks

Disks

Fixed-head disks:

More r/w heads v.s. fast track switching

Moving-head disks (hard disk)

Primary concerns:

Cost, Size, Speed

Computer Æ host controller Æ disk controller Æ disk drives (cache ÅÆ disks)

Floppy disk

slow rotation, low capacity, low density, but less expensive

Tapes: backup or data transfer bet machines

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Storage Hierarchy

register

Main Memory Electronic Disk

Magnetic Disk Optical Disk

Cache

Magnetic Tape

Cost

High hitting rate

• instruction & data cache

• combined cache

Faster than magnetic disk – nonvolatile?!

Alias: RAM Disks

Sequential Access XX GB/350F

Speed

Volatile Storage

I/O Structure

Device controllers are responsible of moving data between the peripheral devices and their local buffer storages.

printer

CPU printer

controller

memory controller

DMA

memory

tape-drive controller

disk

tape drivers

registers buffers registers buffers

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I/O Structure

I/O operation

a. CPU sets up specific controller registers within the controller.

b. Read: devices Æ controller buffers Æ memory

Write: memory Æ controller buffers Æ devices

c. Notify the completion of the operation by triggering an interrupt

DMA

Goal: Release CPU from handling excessive interrupts!

E.g. 9600-baud terminal

2-microsecond service / 1000 microseconds

High-speed device:

2-microsecond service / 4 microseconds

Procedure

Execute the device driver to set up the registers of the DMA controller.

DMA moves blocks of data between the memory and its own buffers.

Transfer from its buffers to its devices.

Interrupt the CPU when the job is done.

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Single-Processor Systems

Characteristics: One Main CPU

Special-Purpose Processors, e.g., Disk-Controller Microprocessors.

Examples:

Personal Computers (Since 1970’s), Mainframes.

Operating Systems

Batching Æ Multiprogramming Æ Time-Sharing

Parallel Systems

Tightly coupled: have more than one

processor in close communication sharing computer bus, clock, and sometimes

memory and peripheral devices

Loosely coupled: otherwise

Advantages

Speedup – Throughput

Lower cost – Economy of Scale

More reliable – Graceful Degradation Æ Fail Soft (detection, diagnosis, correction)

• A Tandem or HP-NonStop fault-tolerance solution

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Parallel Systems

Symmetric multiprocessing model: each processor runs an identical copy of the OS

Asymmetric multiprocessing model: a master- slave relationship

~ Dynamically allocate or pre-allocate tasks

~ Commonly seen in extremely large systems

~ Hardware and software make a difference?

Trend: the dropping of microporcessor cost Î OS functions are offloaded to slave

processors (back-ends)

Parallel Systems

The Recent Trend:

Hyperthreading Processors

Multiple Cores over a Single Chip

N Standard Processors!

Loosely-Coupled Systems

Processors do not share memory or a clock

Blade Servers

Each blade-processor board boots independently and runs its own OS.

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Clustered Systems

Definition: Clustered computers which share storage and are closely linked via LAN networking.

Advantages: high availability, performance improvement, etc.

Types

Asymmetric/symmetric clustering

Parallel clustering – multiple hosts that access the same data on the shared storage.

Distributed Lock Manager (DLM)

Oracle

Operating-System Structure

Simple batch systems

Resident monitor – Automatically transfer control from one job to the next

Spooling (Simultaneous Peripheral Operation On-Line)

Replace sequential-access devices with random-access device

card reader

disks

CPU

disks

printer

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Operating-System Structure

Multiprogramming increases CPU utilization by organizing jobs so that the CPU always has one to execute – Early 1960

Job scheduling and CPU scheduling

Goal : efficient use of scare resources

disk OS job1 job2 job3

Operating-System Structure

Time sharing (or

multitasking) is a logical extension of

multiprogramming!

Started in 1960s and

become common in 1970s.

An interactive (or hand-on) computer system

Multics, IBM OS/360

Virtual Memory

Physical Address

disk

on-line file system virtual memory

sophisticated CPU scheduling job synchronization

protection & security ...

and so on

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Operating-System Operations

An Interrupt-Driven Architecture for Modern OS’s

Events are almost always signaled by the occurrence of an interrupt or a trap (or an exception).

Protection of User Programs and OS

Multiprogramming

Sharing of Hardware and Software

Hardware Protection

Goal:

Prevent errors and misuse!

E.g., input errors of a program in a simple batch operating system

E.g., the modifications of data and code segments of another process or OS

Dual-Mode Operations – a mode bit

User-mode executions except those after a trap or an interrupt occurs.

Monitor-mode (system mode, privileged mode, supervisor mode)

Privileged instruction:machine instructions that may cause harm

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Hardware Protection

System Calls – trap to OS for executing privileged instructions.

Resources to protect

I/O devices, Memory, CPU

I/O Protection (I/O devices are scare resources!)

I/O instructions are privileged.

User programs must issue I/O through OS

User programs can never gain control over the computer in the system mode.

Hardware Protection

Memory Protection

Goal: Prevent a user program from modifying the code or data structures of either the OS or other users!

Instructions to modify the memory space for a process are privileged.

kernel job1

……

job2

…… Limit register

Base register Ù Check for every memory address by hardware

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Hardware Protection

CPU Protection

Goal

Prevent user programs from sucking up CPU power!

Use a timer to implement time-sharing or to compute the current time.

Instructions that modify timers are privileged.

Computer control is turned over to OS for every time-slice of time!

Terms: time-sharing, context switch

System Components – Process Management

Process Management

Process: An Active Entity

Physical and Logical Resources

Memory, I/O buffers, data, etc.

Data Structures Representing Current Activities:

Program Counter Stack

Data Section CPU Registers

….

And More

Program

(code) +

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System Components – Process Management

Services

Process creation and deletion

Process suspension and resumption

Process synchronization

Process communication

Deadlock handling

System Components – Main- Memory Management

Memory: a large array of words or bytes, where each has its own address

OS must keep several programs in memory to improve CPU utilization and user response time

Management algorithms depend on the hardware support

Services

Memory usage and availability

Decision of memory assignment

Memory allocation and deallocation

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System Components – File- System Management

Goal:

A uniform logical view of information storage

Each medium controlled by a device

Magnetic tapes, magnetic disks, optical disks, etc.

OS provides a logical storage unit: File

Formats:

Free form or being formatted rigidly.

General Views:

A sequence of bits, bytes, lines, records

System Components – File- System Management

Services

File creation and deletion

Directory creation and deletion

Primitives for file and directory manipulation

Mapping of files onto secondary storage

File Backup

* Privileges for file access control

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System Components –

Secondary-Storage Management

Goal:

On-line storage medium for programs & data

Backup of main memory

Services for Disk Management

Free-space management

Storage allocation, e.g., continuous allocation

Disk scheduling, e.g., FCFS

System Components –Tertiary Storage Devices

Goals:

Backups of disk data, seldom-used data, and long-term archival storage

Examples:

Magnetic tape drives and their tapes, CD &

DVD drives and platters.

Services – OS Supports or Applications’

Duty

Device mounting and unmounting

Exclusive allocation and freeing

Data transfers from tertiary devices to secondary storage devices.

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System Components – I/O System Management

Goal:

Hide the peculiarities of specific hardware devices from users

Components of an I/O System

A buffering, caching, and spooling system

A general device-driver interface

Drivers

Caching

register

Main Memory Electronic Disk

Magnetic Disk Optical Disk

Cache

Magnetic Tape

Cost

High hitting rate

• instruction & data cache

• combined cache

Faster than magnetic disk – nonvolatile?!

Alias: RAM Disks

Sequential Access XX GB/350F

Speed

Volatile Storage

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Caching

CD/Tape Disk

Memory Cache

Backup by

OS OS

Hardware Compiler

Managed by

20 – 150 1000 – 5000

5000 – 10,000 20,000 –

100,000 Bandwidth

(MB/s)

5,000,000 80 – 250

0.5 – 2.5 0.25 – 0.5

Access Time (ns)

Magnetic Disks CMOS DRAM

On-chip or off- chip CMOS SRAM Custom memory

with multiple ports, CMOS

Implementat ion Strategy

> 100GB

> 16GB

> 16MB

< 1KB Typical Size

Disk Memory

Cache Registers

Name

4 3

2 1

Level

Caching

Information is copied to a faster storage system on a temporary basis

Assumption: Data will be used again soon.

Programmable registers, instr. cache, etc.

Cache Management

Cache Size and the Replacement Policy

Movement of Information Between Hierarchy

Hardware Design & Controlling Operating Systems

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Caching

Coherency and Consistency

Among several storage levels (vertical)

Multitasking vs unitasking

Among units of the same storage level , (horizontal), e.g. cache coherency

Multiprocessor or distributed systems

Memory Cache CPU

Memory cache CPU

Protection and Security

Goal

Resources are only allowed to be accessed by authorized processes.

Definitions:

Protection – any mechanism for controlling the access of processes or users to the resources defined by the computer system.

Security – Defense of a system from

external and internal attacks, e.g., viruses, denial of services, etc.

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Protection and Security

Protected Resources

Files, CPU, memory space, etc.

Protection Services

Detection & controlling mechanisms

Specification mechanisms

Distinguishing of Users

User names and ID’s

Group names and GID’s

Privilege Escalating, e.g., Setuid in Unix

To gain extra permissions for an activity.

Remark: Reliability!

Distributed Systems

Definition: Loosely-Coupled Systems –

processors do not share memory or a clock

Heterogeneous vs Homogeneous

Advantages or Reasons

Resource sharing: computation power, peripheral devices, specialized hardware

Computation speedup: distribute the computation among various sites – load sharing

Reliability: redundancy Æ reliability

Communication: X-window, email

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Distributed Systems

Distributed systems depend on networking for their functionality.

Networks vary by the protocols used.

TCP/IP, ATM, etc.

Types – distance

Local-area network (LAN)

Wide-area network (WAN)

Metropolitan-area network (MAN)

Small-area network – distance of few feet

Media – copper wires, fiber strands, satellite wireless transmission, infrared communication,etc.

Real-Time Embedded Systems

Embedded Computers – Most Prevalent Form of Computers

Have a wide variety ranged from car engines to VCR’s.

General-purpose computers with standard OS’s, HW devices with or without embedded OS’s

Standalone units or members of networks and the Web

Tend to have specific tasks and almost always run real-time operating systems.

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Real-Time Embedded Systems

Definition: A real-time system is a computer system where a timely

response by the computer to external stimuli is vital!

Hard real-time system: The system has failed if a timing constraint, e.g.

deadline, is not met.

All delays in the system must be bounded.

Many advanced features are absent.

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Real-Time Embedded Systems

Soft real-time system: Missing a

timing constraint is serious, but does not necessarily result in a failure

unless it is excessive

A critical task has a higher priority.

Supported in most commercial OS.

Real-time means on-time instead of fast

Multimedia Systems

Multimedia Data

Audio and video files and conventional files

Multimedia data must be delivered

according to certain time restrictions (e.g., 30 frames per second)

Variety on Platforms

Desktop personal computers, Personal Digital Assistant (PDA), cellular

telephones, etc.

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Handheld Systems

E.g., Personal Digital Assistant (PDA) and cellular phones.

New Challenges – convenience vs portability

Limited Size and Weight

Small Memory Size (e.g., 512KB ~ 128MB)

No Virtual Memory

Slow Processor

Battery Power

Small display screen

Web-clipping

Computing Environments

Evolving Environments

Transition from the period of scarce

resources to the period of ubiquitous access!

In the past, portability is achieved by laptops!

Remote access is supported in a limited way.

Mainframes are prevalent!

Now, PC’s, PDA, and various equipments are connected!

High speed networks are available at home and office! Web-computing is popular

(e.g.,portals).

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Computing Environments

Client-Server Systems

Trend: The functionality of clients is improved in the past decades.

Categories:

Compute-server systems

File-server systems

Network Operating Systems

Autonomous computers

A distributed operating system – a single OS controlling the network.

Computing Environments

Peer-to-Peer Systems

Characteristics: Client and server roles depend on whether who is requesting or providing a service.

Network connectivity is an essential component.

Service Availability and Discovery

Registration of services: a centralized lookup service or not

A discovery protocol

Issues:

Legal problems in exchanging files.

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Computing Environments

Web-Based Computing

Web Technology

Portals, network computers, etc.

Network connectivity

New categories of devices

Load balancers

Embedded Computing

Car engines, robots, VCR’s, home automation

Embedded OS’s often have limited features.

Operating System Concepts