1. Chapter 1 Introduction 1.1 What is an operating system
1.2 History of operating systems
1.3 The operating system zoo
1.4 Computer hardware review
1.5 Operating system concepts
1.6 System calls
1.7 Operating system structure

2. Introduction A computer system consists of hardware system programs
application programs

3. What is an Operating System
It is an extended machine
Hides the messy details which must be performed
Presents user with a virtual machine, easier to use
It is a resource manager
Each program gets time with the resource
Each program gets space on the resource

4. History of Operating Systems (1)
First generation
vacuum tubes, plug boards
Second generation
transistors, batch systems
Third generation – 1980
ICs and multiprogramming
Fourth generation 1980 – present
personal computers and workstations (Network operating systems and distributed operating systems)

5. History of Operating Systems (2)
Early batch system
bring cards to 1401
read cards to tape
put tape on 7094 which does computing
put tape on 1401 which prints output

6. History of Operating Systems (3)
Structure of a typical FMS job – 2nd generation

7. History of Operating Systems (4)
Multiprogramming system
three jobs in memory – 3rd generation

8. Fourth generation 1980 – Present
Operating systems for personal computers
CP/M (Control Program for Microcomputers)
DOS (Disk Operating System)  MS-DOS
GUI (Graphical User Interface)
Windows  Windows 95/98/Me
Windows NT  Windows 2000 Windows XP
UNIX:
X Windows, Motif
Linux, Gnome, KDE

9. The Operating System Zoo
Mainframe operating systems
Example: OS/390, OS/360
Server operating systems
Example: UNIX, Windows 2000, Linux
Multiprocessor operating systems
Personal computer operating systems
Windows 98, 2000, XP, Macintosh, Linux
Real-time operating systems
Hard real-time system: the action absolutely must occur at a certain moment.
Embedded operating systems
PalmOS, Pocket PC for PDA
Smart card operating systems
Java Virtual Machine (JVM)

10. Computer Hardware Review (1)
Monitor
Bus
Components of a simple personal computer

11. Computer Hardware Review (CPU)
(a) A three-stage pipeline
(b) A superscalar CPU

12. Computer Hardware Review (Memory)
Typical memory hierarchy
numbers shown are rough approximations

13. Computer Hardware Review (disk)
Structure of a disk drive

14. Computer Hardware Review (5)
One base-limit pair and two base-limit pairs

15. Computer Hardware Review (I/O)
(b)
(a) Steps in starting an I/O device and getting interrupt
(b) How the CPU is interrupted

16. Computer Hardware Review (Buses)
Structure of a large Pentium system

17. Operating System Concepts (Processes)
A process is a program in execution.
The information about a process is stored in an operating system table called the process table.
A process called the command interpreter or shell read commands from a terminal.
If a process can create one or more other process (child processes) and these process create child processes, we can build them in a tree structure.
In UNIX, there is a parent process for all processes.

18. Operating System Concepts (Processes)
A process tree
A created two child processes, B and C
B created three child processes, D, E, and F

19. Processes Tree on a UNIX System

20. Operating System Concepts (Processes)
The communication to cooperate and synchronize processes is called interprocess communication.
A signal causes the process to suspend and run a special signal handling procedure.
Each person authorized to use a system is assigned a UID (User IDentification). A process is assigned a PID (Process IDentification).
Users can be members of groups, each of which has a GID (Group IDentification).
The superuser (root in UNIX) has special privilege to violate many of the protection rules.

21. Operating System Concepts (Deadlocks)
When two or more processes get themselves into a stalemate situation, they are in deadlock.
(a) A potential deadlock. (b) an actual deadlock.

22. Operating System Concepts (Memory & Files)
In virtual memory the operating system keeps part of the address space in main memory and part on disk.
A file system provides users with a nice, clean abstract model of device-independent files.
A directory is used to group files together.
A path name can specify the location of a file.
A root directory is the top of the directory hierarchy. In Unix, / is the root directory.
Each process has a current working directory (pwd).

23. Operating System Concepts (Files)
File system for a university department

24. Operating System Concepts (Files)
If a file access is permitted, the system return small integer called a file descriptor to use in subsequent operations.
In UNIX the mounted file system is used to deal with removable media (mount).
Two kinds of special files exist in UNIX under the /dev directory: block special files (disks) and character special files (printers, modems).
A pipe is a sort of pseudo file that can be used to connect two processes (ps –aef | more).

25. Operating System Concepts (Files)
Before mounting,
files on floppy are inaccessible
After mounting floppy on b,
files on floppy are part of file hierarchy

26. Operating System Concepts (Pipes)
Two processes connected by a pipe

27. Operating System Concepts (Security & Shell)
Files in UNIX are protected by a 9-bit binary protection code.
The protection code consists of three 3-bit fields, one for owner, one for group, and one for others.
Each field has a bit for read, a bit for write, and a bit for execute. They are known as rwx bits.
The UNIX command interpreter is called the shell.
Many shells exist, including sh, csh, ksh, and bash.
The user can use < and > to redirect the standard input and output. The ampersand (&) can be put after a command to start it as a background job.

28. System Calls
System calls provide the interface between a running program and the operating system.
Generally available as assembly-language instructions.
Languages defined to replace assembly language for systems programming allow system calls to be made directly (e.g., C, C++).

29. Steps in Making a System Call
There are 11 steps in making the system call
read (fd, buffer, nbytes)

30. Types of System Calls Process management File management
Directory or Device management
Miscellaneous
Information maintenance
Communications
Some POSIX (Portable Operating System Interface) are listed as follows.

31. Some System Calls For Process Management

32. Some System Calls For File Management

33. Some System Calls For Directory Management

34. Some System Calls For Miscellaneous Tasks

35. System Calls for Process
Process management
File management
Directory or Device management
Miscellaneous
Information maintenance
Communications
Some POSIX (Portable Operating System Interface) are listed as follows.

36. System Calls for Process
Fork creates a duplicate of the original process.
UNIX examples (Fig4-8.c)
fork system call creates new process.
exec system call used after a fork to replace the process’ memory space with a new program.
wait system call used to move the parent process off the ready queue until the termination of the child.
Exit system call is used when a process is finished executing.
Try the ps command.

37. System Calls (Process)
A stripped down shell:
while (TRUE) { /* repeat forever */
type_prompt( ); /* display prompt */
read_command (command, parameters) /* input from terminal */
if (fork() != 0) { /* fork off child process */
/* Parent code */
waitpid( -1, &status, 0); /* wait for child to exit */
} else {
/* Child code */
execve (command, parameters, 0); /* execute command */ }

38. Forking Processes /* fork processes */ main() { int i, pid;
for (i=1; i<=3; i++) {
if ((pid = fork()) == 0) {
printf("In child %d. \n", i); }

39. Forking Processes P
I = 1
I = 2
I = 3
I = 2
I = 3
I = 3
I = 3

40. System Calls for Process
Processes in UNIX have their memory divided up into three segments:
The text segment (the program code)
The data segment (the variables) grows upwards.
The stack segment (functions) grows downwards.

41. System Calls (Process)
Processes have three segments: text, data, stack

42. System Calls (Directory)
link(“/usr/jim/memo”, “/usr/ast/note”);
(a) Two directories before linking /usr/jim/memo to ast's directory
(b) The same directories after linking

43. System Calls (Device) mount(“/dev/fd0”, “/mnt”, 0)
(a) File system before the mount
(b) File system after the mount

44. System Calls (Win32)
Some Win32 API calls

45. Operating System Structure
Monolithic System - "the big mess". All operating system operations are put into a single file. The operating system is a collection of procedures, each of which can call any of the others.
Layered System - The operating system is organized as a hierarchy of layers of processes.
THE operating system
Virtual Machine - The operating system is a timesharing system that provides: (a) multiprogramming and (b) an extended machine.
MS-DOS virtual mode
JVM (Java Virtual Machine)

46. Operating System Structure (Monolithic)
Simple structuring model for a monolithic system

47. Operating System Structure (Layer)
Structure of the THE operating system

48. Operating System Structure
Exokernels - The only job of the operating system is to securely allocate the hardware resources.
Transmeta ?
Client-server Model - The operating system is collection of servers that provide specific services; e.g., file server, etc.
Advantages of client-server model:
Servers are running in user mode. If they crash, the system won’t crash.
Adapt to use in distributed systems.

49. Operating System Structure (Virtual Machine)
Structure of VM/370 with CMS

50. Operating System Structure (Client-server)
The client-server model

51. Operating System Structure (Client-Server)
The client-server model in a distributed system

52. Research on Operating Systems
Most of the papers cited in the research sections were published
ACM –
the IEEE Computer Society –
USENIX –
Microkernel can be made flexible and dependable. It is the current trend.

53. Metric Units
The metric prefixes are typically abbreviated by their first letters, with the units greater than 1 capitalized.
m is for milli and µ is for micro.
For memory, Kilo means 210. For communication, 1-Kbps means 1000 bits per second.

54. Summary: Operating System Components
Main operating system components:
process manager
memory manager
file system

55. Summary: Operating System Components
A process manager controls the creation, execution, and deletion of processes. A process is a program in execution, consisting of:
the executable program,
the program's data and stack,
PC, SP, and other CPU registers,
all other information needed to run the program.

56. Summary: Operating System Components
A process table is a data structure in the operating system that is used to store information about processes – register contents and all other information needed to run the process.
Try experiments Ex1.c and Ex2.c in programs.
Compile using: cc -o forever Ex1.c
cc -o sleepy Ex2.c
Execute in the background: forever &
Print the manual entry for ps: man ps | col -b | lpr –P1 and check the process status for forever.
Print the manual entry for kill and kill the forever process.

57. Summary: Operating System Components
For Ex2.c, look at /usr/include/sys/signal.h.
Note that SIGALRM=14, so we can kill sleepy early by sending signal 14 to process sleepy: kill -14 <pid> where <pid> is the process id of sleepy found by executing ps.
The memory manager manages memory allocation and deallocation.
Most operating systems support multiprogramming to improve CPU efficiency. Multiprogramming simply means that several processes are in memory at the same time.
The memory manager uses swapping and paging to decide which processes (or parts of processes) core images to move between memory and disk.
The motivation is to allow processes which do not fit in memory to be executed anyway and to allow multiprogramming.

58. Summary: Operating System Components
The file system controls access to files on external storage devices, such as disks. Directories are used to organize files. Security and protection is attained by:
assigning each user a unique ID, called a user id (UID),
assigning owners (users) to processes and files, and
using a protection mechanism, such as Access Control Lists (ACL) or Capabilities, to restrict access to processes and files.