whoami
TTIT61:
Process Programming and
Operating
Systems
Alexandru Andrei
Alexandru Andrei, PhD
Embedded Systems Laboratory
Department of Computer and Information Science
Email: alean@ida.liu.se
Phone: 013-322828
alean@ida.liu.se
phone: 013-322828, room: B 3D:439
A. Andrei, Process programming and operating systems, Introduction
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Why Am I Here ?
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Course Material
Process Programming and Operating Systems: TTIT61
http://www.ida.liu.se/~TTIT61
TTIT61=Course+Labs
Course=6 lectures; Exam=2 points
Labs=15 labs; Assignments=2 points
“Resurs”= 4 times (3 sessions dedicated to the labs)
Seventh Edition
Avi Silberschatz
Peter Baer Galvin
Greg Gagne
John Wiley & Sons, Inc.
ISBN 0-471-69466-5
Invited lecture: Thorbjörn Jemander, PhD, Manager
Embedded Platforms, Enea
A. Andrei, Process programming and operating systems, Introduction
A. Andrei, Process programming and operating systems, Introduction
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A. Andrei, Process programming and operating systems, Introduction
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What Is an Operating System?
Lecture Plan
„ Examples of operating systems that you have seen/used.
1. What is an operating system? What are its functions?
Basics of computer architectures. (Part I of the
textbook)
2. Processes, threads, schedulers (Part II , chap. III-V)
3. Synchronization & Deadlock (Part II, chap. VI, VII)
4. Primary memory management. (Part III, chap. VIII, IX)
5. File systems and secondary memory management (Part
IV, chap. X, XI, XII)
6. Security (Part V, chap. XIV)
„
Windows (95, 98, 2000, XP, Vista), DOS
„
UNIX (Solaris, AIX, HP-UX, Linux, BSD, Minix, SunOS)
„
MacOS X
„
OSE, Symbian, RTEMS, RT-Linux, QNX, VxWorks
„
Novell Netware
„ When you buy/get one, what do you get actually?
You get a piece of software!
„ … but when you get Quake, you get a piece of software too! Is Quake an
OS?
A. Andrei, Process programming and operating systems, Introduction
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A. Andrei, Process programming and operating systems, Introduction
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1
Four Components of a Computer System
„ Computer system can be divided into four components
„ Users
† People, machines, other computers
„ Hardware – provides basic computing resources
† CPU, memory, I/O devices
„ Software
† Application programs – define the ways in which the
system resources are used to solve the computing
problems of the users
– Word processors, compilers, web browsers,
database systems, video games
† Operating system
– Controls and coordinates use of hardware among
various applications and users
software
A. Andrei, Process programming and operating systems, Introduction
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Four Components of a Computer System
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Computer System Organization
8
What is an Operating System?
A. Andrei, Process programming and operating systems, Introduction
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Operating System Definition
„ 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
A. Andrei, Process programming and operating systems, Introduction
A. Andrei, Process programming and operating systems, Introduction
„ A program that acts as an intermediary between a user
of a computer or an application and the computer
hardware.
„ Operating system goals:
„ Execute user programs and make solving user
problems easier.
„ Make the computer system convenient to use.
„ Use the computer hardware in an efficient manner.
software
A. Andrei, Process programming and operating systems, Introduction
Computer System Structure
„ OS is a resource allocator
„ Manages all resources
„ Decides between conflicting requests for
efficient and fair resource use
„ OS is a control program
„ Controls execution of programs to prevent
errors and improper use of the computer
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A. Andrei, Process programming and operating systems, Introduction
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2
Operating System Definition (Cont.)
Operating System Definition (Cont.)
„ No universally accepted definition
„ “Everything a vendor ships when you order an operating
system” is good approximation
„ But varies wildly
„ “The one program running at all times on the computer” is
the kernel. Everything else is either a system program
(ships with the operating system) or an application
program
A. Andrei, Process programming and operating systems, Introduction
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Operating System Definition (Cont.)
„ The hardware doesn’t know where the operating system resides
and how to load it
„ Need a special program to do this job – bootstrap loader
„ Typically stored in ROM or EPROM, generally known as
firmware
„ Bootstrap loader locates the OS kernel, loads it into main
memory and starts its execution
„ In some systems, a simple bootstrap loader fetches a more
complex boot program from disk, which in turn loads the kernel
„ GRUB – GRand Unified Bootloader
„ LILO – LInux LOader
„ NTLDR – NT Loader
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Bootstrapping
Bootstrap
loader
RAM
4. Transfers control
to starting location
of operating
system program
with a JMP
instruction.
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Computer Startup
„ No universally accepted definition
„ “Everything a vendor ships when you order an operating
system” is good approximation
„ But varies wildly
„ “The one program running at all times on the computer” is
the kernel. Everything else is either a system program
(ships with the operating system) or an application
program
A. Andrei, Process programming and operating systems, Introduction
A. Andrei, Process programming and operating systems, Introduction
A. Andrei, Process programming and operating systems, Introduction
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What Are the Functions of an OS?
1. When computer is started,
execution begins with bootstrap
loader, permanently stored in
ROM.
2. Bootstrap loader
locates
operating system
program, usually at a
fixed disk location.
3. Loads it into
RAM.
A. Andrei, Process programming and operating systems, Introduction
„ You use your computer to run applications on it. Think of
how you run an application.
The first thing we see at an OS is an interface to run
applications.
„ Could be command line (Unix, DOS) or graphical (MacOS,
Windows). Because it is at the outer layers of an OS, it is
typically called “shell”.
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A. Andrei, Process programming and operating systems, Introduction
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3
User-Operating System Interface:
CLI
User-Operating System Interface:
GUI
„ User-friendly desktop interface
„ Usually mouse, keyboard, and monitor
„ Icons represent files, programs, actions, etc
„ Various mouse buttons over objects in the interface
cause various actions (provide information, options,
execute function, open directory (known as a folder)
„ Invented at Xerox PARC
„ Many systems now include both CLI and GUI interfaces
„ Microsoft Windows is GUI with CLI “command” shell
„ Apple Mac OS X as “Aqua” GUI interface with UNIX
kernel underneath and shells available
„ Solaris is CLI with optional GUI interfaces (Java
Desktop, Gnome, CDE)
„ CLI allows the direct input of commands
„ Sometimes implemented in the kernel, sometimes by
system programs
„ Sometimes multiple flavors implemented – shells
† sh, bash, csh, tcsh (Unix)
„ Primarily fetches a command from user and executes it
† Sometimes commands built-in the shell, sometimes
just names of other programs
– If the latter, adding new features doesn’t require
shell modification
† Shell scripts to automate various jobs (ex. backup,
find specific files and apply a certain command)
A. Andrei, Process programming and operating systems, Introduction
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Starting Applications w/o an OS
„ The OS consists of
„ A user interface for controlling programs (starting,
interrupting)
Addr
Data
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Summary
„ How would we run an application without having an
interface for that?
CPU
A. Andrei, Process programming and operating systems, Introduction
Mem
Ctrl
„ Just put the code of the application in memory at address
X, where X is the address from where the processor starts
to fetch instructions after a power-on.
„ How would we start a second application?
„ Chaining? The first application has to know which is the
second application and has to start it?
A. Andrei, Process programming and operating systems, Introduction
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Hardware Abstraction
A. Andrei, Process programming and operating systems, Introduction
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Hardware Abstraction
„ What means “running an application”? Why do we run
applications?
„ To get some results! On screen, printer, network, files,
soundcard, etc.
„ How does an application put data on the screen, printer,
files, etc., read data from keyboard, network, mouse, etc?
CPU
Mem
HD ctrl
Kbd ctrl
Addr
Data
Ctrl
Network card
ctrl
„ It uses device drivers! (When you buy a network card, you
get a CD with drivers too)
Video card
ctrl
Sound card
ctrl
High-level
Low-level
cmd
cmd
Application code
Device driver
Device controller
High-level response
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Low-level response
A. Andrei, Process programming and operating systems, Introduction
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Device Drivers
Summary
„ How would applications interact with the hardware if there
was no OS?
„ The OS consists of
„ A user interface for controlling programs (starting,
interrupting)
„ A set of device drivers for accessing the hardware
„ The device driver code has to be included in the
application code.
„ Portable applications? What if I change my soundcard?
„ Security? If everyone has access to the whole
hardware, any user could read any hard-disk sector.
„ Safety? What if I make errors in my program?
A. Andrei, Process programming and operating systems, Introduction
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Hardware Abstraction
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System Calls
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h>
#include <sys/types.h>
/* System calls are written in bold italic. Type “man 2 sys_call_name” for info in
Linux or “man –s 2 sys_call_name” in Solaris */
int fd, n;
char buf[1024];
„ The device drivers are part of the OS.
„ The application requests a service from the drivers (OS).
„ Known as “system calls”, in this case device-oriented
system calls.
fd = open(“datafile.txt”, O_RDWR);
n = read(fd, buf, 1024);
printf(“Have read %d bytes: %s\n”, n, buf);
lseek(fd, 0, SEEK_SET);
write(fd, “Some other text”, strlen(“Some other text”) + 1);
write(fd, buf, n);
close(fd);
„ The set of system calls can be seen as the API of the OS.
A. Andrei, Process programming and operating systems, Introduction
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System Calls
A. Andrei, Process programming and operating systems, Introduction
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System Call Execution
USER
Shell
Application
program
System calls interface
File
services
I/O
services
Process
Management
Memory
Management
Computer
hardware
A. Andrei, Process programming and operating systems, Introduction
OS KERNEL
Network
services
Operating
system
Network
hardware
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A. Andrei, Process programming and operating systems, Introduction
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5
Summary
Process Management
„ The OS consists of
„ An user interface for controlling programs (starting,
interrupting)
„ A set of device drivers for accessing the hardware
„ An set of system calls as a program interface to
hardware (a lot more during the labs !)
A. Andrei, Process programming and operating systems, Introduction
„ Can you run two or more programs at the same time on
your computer?
„ Do they really run at the same time (i.e. concurrently)?
„ Many desktop PCs and laptops have 1 CPU, and 1 CPU
may run only one program at a time. The programs run
pseudo-concurrently. A pseudo-parallelism obtained by
execution interleaving (multiprogramming).
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executing
Process 2
I/O
CPU
waiting
executing
Process 3
executing
I/O
executing
„ The OS schedules several processes
„ It manages process data such that
„ Processes may resume their execution from where they
were interrupted
„ Their requests for resources (I/O, memory) do not
interfere
† E.g.: Process A accesses the hard disk through
some system call at time 0. Process B is scheduled
at time 1ms. The hard disk sends an interrupt at time
2ms signalling that it has completed the request
made at time 0. The interrupt should not reach to
process B, just that the hard disk controller knows
nothing about processes.
executing
waiting
executing
executing
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Process Management
Process Execution
Process 1
A. Andrei, Process programming and operating systems, Introduction
I/O
…
A. Andrei, Process programming and operating systems, Introduction
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Process Management
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Summary
„ The OS consists of
„ A user interface for controlling programs (starting,
interrupting)
„ A set of device drivers for accessing the hardware
„ A set of system calls as a program interface to hardware
(and not only, we’ll see later)
„ Process manager (scheduler) that schedules process
execution and manages the process state
„ Could we implement pseudo-concurrent execution without
an OS?
„ Each program would have to know about at least one other
program, to relinquish the processor and to activate the
next program.
„ We would need a way to chain programs. Almost
impossible.
A. Andrei, Process programming and operating systems, Introduction
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A. Andrei, Process programming and operating systems, Introduction
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6
FreeBSD Running Multiple
Programs
Memory in MS-DOS
(a) at system startup
(b) running a program
Memory layout
A. Andrei, Process programming and operating systems, Introduction
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Memory Management
int a[20];
printf(“%d\n”, a[i] – 5);
stack
0xfffffffc
0xfffffff8
0x00
0x08
0x00
0x00
0x00
0x00
0x00
0x40
0x25
0x0f
0x64
0x00
0x05
0x08
0xfffffff4
.data
0x40000000
0x40000004
0x0a
0x00
0x00
0x00
0x40000008
…
0x40000044
0x00
0x00
„ What to remember from the previous slide:
„ Programs are laid out in memory as code, data (read-only,
initialized, not-initialized), and stack segments.
„ Variables in high-level programs correspond to memory
locations
„ Accesses to a variable (for reading and writing them)
corresponds in the code to accesses in the memory at the
address of the memory location that corresponds to the
variable.
„ Items from the memory are accessed using their address
„ How should a compiler decide at which address to put each
variable? How are clashes avoided when there are several
programs that run on the same system?
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Memory Management
A. Andrei, Process programming and operating systems, Introduction
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Summary
„ Naïve solutions to the memory management problem:
„ Only one program in memory at the same time. Whenever the
scheduler selects a new program to execute, the old one is
swapped out on a secondary device (HDD). The memory image
of the new program is swapped in from the secondary device.
„ Pre-allocation by a global authority of the memory space to all
software developers
„ All addresses that appear in the program are relative to a base
address given by the OS upon loading the program in memory.
„ Modern solutions:
„ Programs know about virtual memory and do not know the
physical address that will be put on the address bus
„ Operating system translates virtual addresses to physical
addresses (more during the course and labs).
A. Andrei, Process programming and operating systems, Introduction
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Memory Management
.section .rodata
.lc0: .string “%d\n”
.comm i,4
.comm a,80
%esp .text
subl $8, %esp
movl .lc0, (%esp)
%d\n
movl i, %eax
i
movl a(,%eax,4), %eax
a[0]
subl $5, %eax
a[i]
movl %eax, 4(%esp)
call printf
A. Andrei, Process programming and operating systems, Introduction
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„ The OS consists of
„ A user interface for controlling programs (starting,
interrupting)
„ A set of device drivers for accessing the hardware
„ A set of system calls as a program interface to hardware
(and not only, we’ll see later)
„ Process scheduler that schedules process execution
and manages the process state
„ Memory management
A. Andrei, Process programming and operating systems, Introduction
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7
File System
Summary
„ The OS consists of
„ A user interface for controlling programs (starting,
interrupting)
„ A set of device drivers for accessing the hardware
„ A set of system calls as a program interface to hardware
(and not only, we’ll see later)
„ Process scheduler that schedules process execution
and manages the process state
„ Memory management
„ File system
„ The organization of a HDD as it comes from the
manufacturer is given in C/H/S (cylinders, heads, sectors)
„ Unsuitable for a hierarchical file system
„ The OS abstracts away the C/H/S and presents to the user
a file-system interface
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Other Functions
„ The OS consists of
„ A user interface for controlling programs (starting,
interrupting)
„ A set of device drivers for accessing the hardware
„ A set of system calls as a program interface to hardware
(and not only, we’ll see later)
„ Process scheduler that schedules process execution
and manages the process state
„ Memory management
„ File system
„ Others
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Operating System Design and
Implementation
A. Andrei, Process programming and operating systems, Introduction
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Simple Structure
„ Design and Implementation of OS not easy, but some
approaches have proven successful
„ Internal structure of different Operating Systems can vary
widely
„ Start by defining goals and specifications
„ Affected by choice of hardware, type of system
„ User goals and System goals
„ User goals – operating system should be convenient to
use, easy to learn, reliable, safe, and fast
„ System goals – operating system should be easy to
design, implement, and maintain, as well as flexible,
reliable, error-free, and efficient
A. Andrei, Process programming and operating systems, Introduction
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Summary
„ Support for inter-process communication (message
queues, synchronization mechanisms, shared memory
segments)
„ Support for security (system of access control lists,
capability lists, etc.)
„ Interfaces for performance estimation, profiling, debug,
statistics, board configurations, on-board sensor
monitoring, etc. (see the /proc file system on Linux for
example)
„ Support for fault-tolerance (RAID arrays)
„ Support for various optimizations (battery life, for example)
A. Andrei, Process programming and operating systems, Introduction
A. Andrei, Process programming and operating systems, Introduction
„ MS-DOS – written to provide the most functionality in the
least space
„ Not divided into modules
„ Although MS-DOS has some structure, its interfaces
and levels of functionality are not well separated
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A. Andrei, Process programming and operating systems, Introduction
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8
MS-DOS Layer Structure
Layered Approach
„ 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
A. Andrei, Process programming and operating systems, Introduction
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Layered Operating System
A. Andrei, Process programming and operating systems, Introduction
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UNIX
„ UNIX – limited by hardware functionality, the original
UNIX operating system had limited structuring. The
UNIX OS consists of two separable parts
„ Systems programs
„ The kernel
† Consists of everything below the system-call
interface and above the physical hardware
† Provides the file system, CPU scheduling,
memory management, and other operatingsystem functions; a large number of functions
for one level
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UNIX System Structure
A. Andrei, Process programming and operating systems, Introduction
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Microkernel
„ Minimum essential functionality in the kernel, the rest
implemented as system services
„ Client-server system on same system
„ Clients request services from microkernel which
passes message onto appropriate server
A. Andrei, Process programming and operating systems, Introduction
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Microkernel System Structure
Modules
„ Moves as much from the kernel into “user” space
„ Communication takes place between user modules using
message passing
„ Benefits:
„ Easier to extend a microkernel
„ Easier to port the operating system to new architectures
„ More reliable (less code is running in kernel mode)
„ More secure
„ Detriments:
„ Performance overhead of user space to kernel space
communication
A. Andrei, Process programming and operating systems, Introduction
„ 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
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Solaris Modular Approach
A. Andrei, Process programming and operating systems, Introduction
A. Andrei, Process programming and operating systems, Introduction
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Windows XP Architecture
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Solaris Kernel Overview
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Reading
„ Silberschatz, Galvin, Gagne, 7th edition, Part I
„ Chapter 1: 1.1-1.9
„ Chapter 2: 2.1-2.7, 2.10
Richard McDougall, James Mauro at LISA’06
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