1. Lecture 3: Basic OS Concepts

2. Review: Operating Systems History
: Batch Systems – Cards
: Spooling Batch Systems – Tapes
1960- : Multiprogramming
1970- : Timesharing
1990- : Real-time, Distributed
2005-: WebOS (Web2.0, etc)
2007-: Mobile OS
All programming was done in absolute machine language, vacuum tubes vs transistor

3. Review: The Operating System Zoo
Personal computer operating systems
Single user (usually)
MS-DOS, Windows, Linux
Server operating systems
Focus on networking
Linux, SunOS, Windows NT
Multiprocessor operating systems
Real-time operating systems
Hard versus soft real-time OS
Embedded operating systems
Memory, power constraints
Smart card operating systems
Extreme resource constraints
Mobile Operating Systems
Android, iOS, Android Wear

4. Review: Computer Hardware
Monitor
Bus
Components of a simple personal computer

5. Overview of this lecture
Process
File systems
System calls

6. Program vs. Process A process is a program in execution
Program is a piece of code
Process has “state” (what could this state be?)
There could be multiple processes all simultaneously executing the same program
Coordinate accesses and sharing of resources
Sharing in time – CPU cycles
Sharing in space – Memory

7. Processes Process = program in execution
Address space
Program (text), data, stack
Registers
Program counter, stack pointer, etc
Processes can be created, suspended, restarted, killed (!)
Process scheduler decides which process to run next among all the current processes

8. Process Creation
In UNIX, there is a way for one process to “spawn” more processes
A process tree
Process A created two child processes, B and C
Process B created three child processes, D, E, and F

9. Processes: Memory Sharing
Operating System
Physical memory

10. Inter process communication (UNIX)
A pipe is like a pseudo file.
Processes set up a pipe in advance.
Processes read from or write to a pipe.

11. Mounting Files (UNIX) Before mounting, After mounting floppy on b,
files on floppy/CD-ROM are inaccessible
After mounting floppy on b,
files on floppy/CD-ROM are part of file hierarchy

12. File Permissions Example
% ls -lR .:
total 2
drwxr-x--x 2 guan adm Dec 17 13:34 A
drwxr guan adm Dec 17 13:34 B
./A:
total 1
-rw-rw-rw- 1 guan adm Dec 17 13:34 x
./B:
-r--rw-rw- 1 guan adm Dec 17 13:34 x
-rw----rw- 1 trina adm Dec 17 13:45 y
Show an example, man, ls, chmod
Copyright © 2002 Thomas W. Doeppner. All rights reserved.

13. Setting File Permissions
#include <sys/types.h>
#include <sys/stat.h>
int chmod(const char *path, mode_t mode)
only the owner of a file and the superuser may change its permissions
nine combinable possibilities for mode (read/write/execute for user, group, and others)
S_IRUSR (0400), S_IWUSR (0200), S_IXUSR (0100)
S_IRGRP (040), S_IWGRP (020), S_IXGRP (010)
S_IROTH (04), S_IWOTH (02), S_IXOTH (01)
Symbolic mode
Chmod o-x file
Copyright © 2002 Thomas W. Doeppner. All rights reserved.

14. Structure of UNIX
Shell
User Input
Kernel (OS)

15. System Calls
Interface between the user and the operating system (kernel)
Handle processes, files, directories, time, input/output
Switch processor from user to kernel mode
In User mode, some instructions are forbidden
In Kernel mode, all instructions are allowed

16. Example Read from file n = read(fd, buffer, nbytes);
Change directory s = chdir(dirname);
Get time s = time(&seconds);

17. System Calls For File Management

18. System Calls For Directory Management

19. System Calls For Miscellaneous Tasks

20. Quick Questions Does this belong in the OS?
Text editor
Compiler
Web browser
Shell
client
Program which copies files
Device driver (program which controls a hardware device)