Introduction to Operating Systemsdase.ecnu.edu.cn/mgao/OS_2015/slides/1_OS overview.pdf · OS 360:...

Introduction to Operating SystemsLecture 1: Operating system overview

MING GAO

SE@ecnu(for course related communications)

[email protected]

Mar. 2, 2015

Outline

1 What is an Operating Systems?

2 Co-evolution of computer systems and operating systemsCS overviewOS historyOS structures

MING GAO (SE@ecnu) Introduction to Operating Systems Mar. 2, 2015 2 / 56

what

What’s an OS?

A conceptual framework of a computer system


what

Two point-of-views

Machine interface: resource manager

How do programs run on CPUs simultaneously?

Whatif the memory is used off?

How is a file stored and accessed?

Whatif two uses send printing job to the same printer at the sametime?

...

Human (programmer) interface: virtual machine

cont’d in the next slide


what

Two point-of-views

Machine interface: resource manager

Human (programmer) interface: virtual machine

You (a process) have all CPU time and memory

You are the single owner of all devices

Different devices have same interfaces

Device interfaces are more powerful than raw hardware

...


what

Two point-of-views


what

Definitions of OS

“An OS is similar to the government”

“Everything a vendor ships when you order an operating system”

“An operating system implements a virtual machine that is (hopefully)easier and safer to program and use than the raw hardware”

“The one program running at all times on the computer” is thekernel.

Everything else is either a system program (ships with the operatingsystem) or an application program


what

Why do SEI students study OS?

As a programmer

You should know:

What does it meanSegmentation faulthere?

Why does it happen?

How to solve it?


what


As a programmer

And:

Why there is noSegmentation faultnow?


what


As a programmer/QA

How many methods are there to allocate memory/storage?

What are their differences?

Which one is appropriate when you need 1KB, 100KB, 1MB, 100MB,or 1GB storage in a machine with 128MB, 512MB, 1GB, or 4GBmain memory? Why?

This is only a tiny technical issue in coding, and maybe you know theanswer intuitively.

But you need to know OS well to make sure that all your decisionsare reasonable.


what


As a software designer

Given a computer, to determine appropriate functions that can runsmoothly

To design the process/thread structure, memory usage, fileorganization, etc.

Many issues related to performance, availability, robustness etc shouldbe considered based on deep understanding to OS


what


As a system administrator

Hundreds or even thousands of parameters to be setup or tuned

What do “circular logging” mean?

What to do when a system runs overloaded? (graceful degradation)

Buy new hardware?Tune parameters?Limit users’ activities?

It’s not that simple! An inappropriate action may overload the systemfurther.


what


As a manager (tech.-related)

You need solid knowledge and be rational before decision making

You need to be a qualified user and technical worker before being agood manager


CS-OS co-evolution CS overview

An overview of OS

Before that, we need to look close at the computer system.



An overview of a computer system



CS overview: Issues

CPU(s) and I/O devices may execute simultaneously

CPU is expensive

There may be conflicts in memory access and bus

There is speed mismatch

Device start-up or warm-up is usually slow



CPU: A simplified, ideal architecture



CPU issues

One or some CPUs, many programs running simultaneously

Browser (with several windows), MSN/QQ, MS Word, MS OutlookExpress,

Anti Virus, Printer Manager, ... There are conflicts and needcoordination!

When you are writing a program (so you are a programmer now), youdon’t know what other programs will be running with yours



I/O



I/O issues

CPU-I/O, memory-I/O speed mismatch

Various devices: you need a/limited unified interfaces

Mode: character/block, sync/async, buffering...SpeedController/driver details

Limited capabilities: you need some more advanced interfaces

Try to write a program that uses serial port to communicate



Storage hierarchy



Storage issues

Size mismatch

You cannot put all things in to main memory

Even your program (and its data) can, the sum of all programs can’t!

Speed mismatch

You should try to put your data (including programs) as close to theCPU as you can (as high as possible)

Allocation, addressing, and organization

Who will do this for you?


CS-OS co-evolution OS history

Moore’s Law



My own experience



CS-OS co-evolution

1948 - 1970 hardware expensive, human cheap

1970 - 1985 hardware cheaper, human expensive

1985 - hardware very cheap, human very expensive

1989 - distributed systems

1995 - mobile systems



1948 - 1970:Hardware expensive (M$), human cheap

Aim: Optimize for more efficient use of the hardware

OS Batch monitor

Load program, run, printNo protection

Users Wait when the program is running



Interrupts

Obervations

The behavior of programs: “compute, I/O, compute, ...”

CPU is much faster than I/O

Must CPU wait when I/O is processing?

CPU time is expensive!

Ideas

I/O can be completed asynchronously

Trap: Software-generated interrupt caused either by an error or a userrequest.

An OS is interrupt-driven



Interrupts



Interrupts

Interrupt handling

Interrupt transfers control to the interrupt service routine, throughthe interrupt vector, which contains the addresses of all the serviceroutines.

Interrupt architecture must save the address of the interruptedinstruction.

The OS preserves the state of the CPU by storing registers and theprogram counter.

Incoming interrupts are disabled while another interrupt is beingprocessed to prevent a lost interrupt.

Interrupts may be nested (based on priorities)



Multi-programming

Observations

The behaviors of programs: “compute, I/O, compute, ...”

When one program is waiting I/O, should other ones wait too?

CPU time is expensive!

How?

Idea Several programs run simultaneously

Issue Need memory protection between programs and/or OS



Complexity of OS

Multics: announced in 1963, ran in 1969

1777 people “contributed to Multics” (30-40 core dev)

Turing award lecture from Fernando Corbato (key researcher): “Onbuilding systems that will fail”

OS 360: released with 1000 known bugs (APARs)

“Anomalous Program Activity Report”

OS finally becomes an important science

How to deal with complexity?



1970 - 1985:HW cheaper (104$), human expensive

Observations

Users need to debug, edit, and use email online, simultaneouslyResponse time is important for user experience

Idea Time-sharing

Use cheap terminals (K$) to let multiple users interactwith the system at the same timeSacrifice CPU time to get better response time

Issue Thrashing

Performance varies non-linearly w.r.t. loadCaused by many factors including swapping andqueueing



1985 - :HW very cheap (K$), human very expensive

Observations

Requirements and possibilities of personal computing

Limited hardware resource initially

PCs become powerful eventually (Moore’s Law)

Ideas

OS as a subroutine library (DOS, CP/M) for limited HW

Less protection for PC?

OS regains all the complexity of a big OS



1989 - : Distributed systems

Observations

Networking (Local Area Networking, LAN)

Ideas: Distributed OS vs. Network OS

Resource (computing, file storage, devices, services) sharing

Client-Server (C/S) model

Web Server, file server, printer server, database server, . . .

Peer-to-Peer (P2P) computing

Web-based computing

Considering Google Apps. (Gmail, Gtalk, G-Office suite, G-notebook,G-pages, G-reader, G-calendar, G-groups, ...) that emulates afull-featured desktop



1995 - : Mobile systems

Observations

Ubiquitous mobile devices with limited capabilities: Laptops, PDAs, mobilephones, . . .Wireless/Wide-area networking

Ideas

Resource (computing, file storage, devices, services) sharing

Handheld systems and OS

P2P computing

Web-based computing



More on CS/OS co-evolution

Real-time embedded systems : Real-time OS, Embedded OS

Multimedia systems

Multiprocessor systems :

For high throughput, scalability and reliabilityMulti-core CPUsParallel computing

Clustered systems :

For high availabilityGoogle File System/Map-Reduce


CS-OS co-evolution OS structures

OS components

Process management

Main memory management

I/O system management

File management

Networking

User interfaces



OS services

Helpful to users

User interfaces

Program execution

I/O operations

File-system manipulation

Communications

Error detection

Helpful to the system itself



OS services

Helpful to users

Helpful to the system itself

Error detection & recovery

Resource allocation

Accounting

Protection and security



User/OS interfaces

CLI (Command Line Interface)

Sometimes in kernel, sometimes provided by system program (shells)

For built-in features (in kernel) or external programs

GUI (Graphical User Interface)

User-friendly desktop metaphor interface

With help of mouse, keyboard, and monitor

Invented at Xerox PARC

System calls



System calls

Programming interface to the services provided by the OS

Typically written in a high-level language (C or C++)

Mostly accessed by programs via a high-level Application ProgramInterface (API) rather than direct system call use

Typically, a number associated with each system call

System-call interface maintains a table indexed according to thesenumbersWith parameter-passing (via register, block/table, or stack)



System calls



Dual-mode operation



OS structures

Simple Only one or two levels of code

Layered Lower levels independent of upper levels

Microkernel OS built from many user-level processes

Modular Core kernel with dynamically loadable modules



MS DOS: Simple structure

MS DOS

Written to provide the most function-ality in the least space

Not divided into modules

Interfaces and levels offunctionality not well separated



UNIX: Also simple structure

UNIX - limited by hardware functionality

Original UNIX operating system consists of two separable parts:

Systems programs

The kernel :

Consists of everything below the system-call interfaceand above the physical hardware;Provides the file system, CPU scheduling, memorymanagement, and other operating-system functions;Many interacting functions for one level



Layered structure

The operating system is divided into a number of layers (levels),

Each built on top of lower layers.

The bottom layer (layer 0), is the hardware;

The highest (layer N) is the user interface.

With modularity, layers are selected such that each uses functions(operations) and services of only lower-level layers

Not always possible

There are machine dependant layers and independent layers



Layered structure



Micro-kernel structure

Ideas

Moves as much from thekernel into “user” space

Small core OS running atkernel level

OS services built frommany independentuser-level processes

Communication betweenmodules with message passing

Benefits

1 Easier to extend amicro-kernel

2 Easier to port OS to newarchitectures

3 More reliable (less code isrunning in kernel mode)

4 Fault Isolation (parts ofkernel protected from otherparts)

5 More secure

Detriments

Performance overhead severe for naive implementation



Module-based structure

Most modern operating systems implement kernel modules

Uses object-oriented approach

Each core component is separate

Each talks to the others over known interfaces

Each is loadable as needed within the kernel

Overall, similar to layers but with more flexible



Virtual machines

What? It takes the layered approach to its logical conclusion. Ittreats hardware and the operating system kernel as thoughthey were all hardware

How? The OS creates the illusion of multiple processes, eachexecuting on its own processor with its own (virtual) memory

Why? Benefits:

Programming simplicityFault isolationProtection and portability



Virtual machines

VMWare



OS implementation issues

Policy vs. Mechanism: Should be separated, since both change

Policy: What do you want to do?Mechanism: How are you going to do it?

Algorithms used

Linear, Tree-based, Log Structured, etc . . .

Event models used

threads vs. event loops

Backward compatibility issues

System generation/configuration

How to make generic OS fit on specific hardware


Take-home msg.

Terms and their Chinese translations


Take-home msg.

Take-aways

Two point-of-views

CS-OS co-evolutionOS design: Application-driven

Dual-mode operation

Some important concepts

Everything exist with a reason!


Take-home msg.

Acknowledgement

Many slides are copied or adapted from:

Slides provided by authors of the textbook(http://codex.cs.yale.edu/avi/os-book/os7/)

Prof. Anthony D. Joseph’s slides for course CS162 (2006) atEECS@UCBerkeley (http://inst.eecs.berkeley.edu/~cs162)(Copyright @ 2008 UCB)


http://codex.cs.yale.edu/avi/os-book/os7/

http://inst.eecs.berkeley.edu/~cs162

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