Adapted from the slides prepared by Alan Feuer Some material from Operating System Concepts by Silberschatz et. al. and Modern Operating Systems by Tanenbaum

Adapted from the slides prepared by Alan FeuerSome material from Operating System Concepts by Silberschatz et. al. and Modern Operating Systems by Tanenbaum 1

CS U480: Systems & Networks

1. Introduction

Donghui Zhang


Syllabus

Instructor: Donghui Zhang

Class page linked from my home page:

http://www.ccs.neu.edu/home/donghui


Your Background

CSU380: Computer organization System architecture: Processors, memory, I/O devices Processor architecture: ALU, instruction execution Assembly-level programming

C/C++ programming Familiarity with the C language and the standard C library

Please consult with me if you are unsure your background is sufficient


Why Programming

For CS: must. A pilot must know how to fly an airplane.

For IS: also important. A project manager needs to have technical

background. Bill Gates used to be a superb programmer. Guest speaker: Prof. Hafner.


Why C (and not Java)

Talked with Mr. Feuer and Prof. Hafner. We provide guidance to what you should learn.

(If you say “give us A without any exam or project”…)

Most OS are implemented in C. Java hides many low-level details. This is a place to strengthen your C skills.


What is an Operating System?

An operating system is a program that acts as an intermediary between a user of a computer and the computer hardware.

Goals: Execute user programs and make solving user problems easier. Make the computer system convenient to use.

Performance measures: Throughput: The total amount of work done over a period of time. Turnaround: The total time it takes to complete a job.


Concept Map

CPU ALU Registers

Peripherals Disks Keyboard Mouse Display

Applications GUI Console

OS

Memory


Software Layers

A

Applicationc = getc()

Libraryread(…)

Operating System kb_driver_read(…)

Device driverread_device(…)


Compilation vs. Execution During compilation, statements in higher-level

languages are converted into machine code During execution, machine code is interpreted by a

processor

Memory

Compiler

High-level language program

Assembly language

Assembler

Machine code

Link editor

Libraries ofMachine code

Executable

SharedLibraries

OperatingSystem

DeviceDrivers


Evolution of the OS

In the beginning Whirlwind at MIT PDP-1 from DEC Altair from MITS

Program stored in a hardware patch board or toggled in using switches

Program can access all of memory Program starts at location zero

Loading programs by hand is slow and error-prone and painful, so . . .

Memory

Program

0

n


Create a very short program to load longer programs Toggle in bootstrap loader Primitive loader may load in

program or a more complex loader to read from cards or tape

Loading from cards is very slow, often took longer to load than to run, wasting (expensive) processor cycles, so . . .

Memory

Loader

Program

0

n

Evolution of the OS: The Loader


Jobs are spooled on tape While one batch of jobs is

running, card reader writes next batch of jobs on tape

Jobs are read sequentially from tape into memory

Tape is still relatively slow compared to processing

Memory

Batch Loader

Program

0

n

Evolution of the OS: Batch Processing


With the introduction of programming languages, a translator is needed to convert a program into machine code• When a program is stored on cards in the

programming language, e.g., assembler or Fortran, it must be translated before it can be run

• Example: To run a program written in Fortran

1. Load (machine code for) Fortran compiler

2. Run compiler:

Compiler reads program, writes machine code

3. Load (machine code for) program

4. Run program

The Concept of a Job


Load next program while previous program is running

But now both programs can’t begin at address zero (in fact, starting address isn’t known in advance)

Solutions? Programs that perform lots of I/O

waste (expensive) processor cycles

Memory

Loader

Program 1

Program 2

0

n

Evolution of the OS: Multiprogramming


Share execution time among programs

When one program starts I/O, let the other run.

What is needed to switch from one program to another?

A program bug in one program can overwrite another program, or the system programs and data, so . . .

Memory

Loader + scheduler

Program 1

Program 2

System data

0

n

Evolution of the OS: Multitasking


Run programs in separate address spaces

System programs need to cross address spaces.

System runs in privileged mode. The more programs in memory,

the less memory available for each program, so . . .

Memory

Loader, scheduler, memory mgr

Program 1

Program 2

System data

Program 3

0

n

Evolution of the OS: Protection


Address space implemented in both main and secondary memory

Broken into pages A program’s address space is

a set of pages. The address space for a program

may be larger than main memory! Pages are swapped in and out of

main memory as needed.

Memory

Loader, scheduler, memory mgr, resource mgr

Disk0

n

Evolution of the OS: Virtual Memory


OS Diversity

Great diversity of programmable hardware Super computers: simulation, scene generation, data mining Servers: database, web, video Personal: desktop, laptop Embedded: PDA, phone, media device

Nature of the OS depends on Application mix Hardware capability Real-time requirements

With the proliferation of embedded systems, most processors do not run a general purpose OS


OSes are complex programs developed over many years by many people

They confront common problems that reappear in other contexts The problems have been formalized A variety of solutions have been proposed and implemented Choosing a solution requires evaluating tradeoffs of space,

time, and complexity OSes are a rich source of well-designed sample programs

We will study OSes by exploring common components Understand the motivation for each component Understand the tradeoffs for each implementation


Common System Components

Process Management Main-Memory Management File System I/O System Network Management

Let’s take a high-level tour of these components


Process Management

A process is a program in execution To accomplish its task, a process needs certain resources:

CPU time Memory Files I/O devices.

The OS is responsible for the following activities in connection with processes:

Process creation and deletion Process suspension and resumption Mechanisms for:

Process synchronization Inter-process communication


From Program to Process

Memory

Compiler

High-level language program

Assembly language

Assembler

Machine code

Link editor

Libraries ofMachine code

Executable

SharedLibraries

OperatingSystem

DeviceDrivers

ProgramProcess


Memory Management

Main memory is a large array of words Each word (or, often byte) has its own address Data in memory is shared by the CPU and I/O devices

Main memory is (usually) volatile It loses its contents in the case of system failure.

The OS is responsible for the following activities in connection with memory management:

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.


Memory Management (cont.)

Memory

Loader, scheduler, memory mgr

Program 1

Program 2

System data

Program 3

0

n


Secondary-Storage Management

Secondary storage is (usually) a large array of blocks Each block has its own address Data is moved between main memory and secondary storage in

units of blocks

Secondary storage is non-volatile and can be very large Disks are the most common in general purpose systems Memory cards and stick are common on portable devices

The OS is responsible for the following activities in connection with secondary storage management:

Free space management Storage allocation For disks, scheduling of block transfers


Secondary-Storage Management (cont.)

Memory

Loader, scheduler, memory mgr, resource mgr

Disk0

n


File Management

A file is a collection of related information Files are stored within a file system From the view of most systems, a file is an array of bytes

The OS is responsible for the following activities in connections with file management:

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 (nonvolatile) storage media


I/O System Management

Input/Output refers to the movement of data between main memory and peripheral devices

Devices vary widely in their operation and behavior Devices are partitioned into classes to factor common

behavior A device driver translates between general OS operations

and device-specific commands

I/O managements consists of A buffer-caching system A general device-driver interface Drivers for specific hardware devices


I/O System Management (cont.)


Network Management

Networking allows distinct computer systems to exchange data

Communication takes place using a protocol Networked computers vary widely in their degree of coupling:

They may share a common OS and processes may be visible across systems

They may share nothing except a communication port

Networking allows users to access to non-local resources, allowing:

Computation speed-up, through special purpose hardware or parallel processing

Availability of data from other systems Enhanced reliability through redundancy


Network Management (cont.)

Documents

Adapted from the slides prepared by Alan Feuer Some material from Operating System Concepts by Silberschatz et. al. and Modern Operating Systems by Tanenbaum