1. Basic UNIX Concepts

2. Why We Need an Operating System (OS) OS interacts with hardware and manages programs. A safe environment for programs to run is required. Programs not expected to know which hardware they will run on. Must be possible to change hardware without changing the programs.

3. In Computing Today It Is Desirable To Be Multiprogramming: Multiple programs can be in memory. Multiuser: Multiple users can be on system. Multitasking: One user can run multiple programs.

4. What an OS Does When a Program Runs on a Computer OS loads program from disk and allocates memory and CPU. Instructions in program are run on CPU and OS keeps track of last instruction executed. If program needs to access the hardware, OS does the job on its behalf. OS saves the state of the program if program has to leave CPU temporarily. OS cleans up memory and registers after process has completed execution.

5. A Little UNIX History 1969 Richie/Thompson at Bell Labs (AT&T) invent UNIX BSD UNIX from Berkeley created from AT&T version Fragmentation grows: Solaris, AIX, HP-UX, Tru64 UNIX System V from AT&T (SVR4) attempts unification AT&T -> Novell -> X/OPEN -> The Open Group (own trademark)

6. A Little UNIX History (continued) Early 80’s: BSD UNIX contains TCP/IP spurring growth of Internet Early 80’s: MIT develops X Windows, a windowing system for UNIX 1991: Linus Torvalds develops Linux, a free UNIX implementation IEEE POSIX – Portable Operating System Interface (for UNIX) –Defines standardized UNIX computing environment –OSs based on UNIX can claim conformity 2001: Single UNIX Specification Version 3 (SUSV3)

7. What Makes Unix Special It is written in a high-level language, C. Everything in the system is represented as a file – containers for information. Work gets done by processes – representations of programs in execution. Workload shared by two separate programs, the kernel and the shell Kernel - the core OS Shell – the interface between user and kernel (command line interpreter) Kernel uses system calls to do most of the work.

8. What Makes Unix Special (continued) It is multiprogramming, multitasking, and multiuser. UNIX ships with many useful tools (e.g., compilers, interpreters, filters, …). “Small is beautiful” philosophy. Pipes connect output of one command to the input of another command (e.g., who | wc ). UNIX provides strong pattern matching features (e.g., *.c) The shell is also a programming language (shell scripts) Online help is provided through the man command..

9. UNIX Architecture: The Kernel Loaded by the bootstrap program at startup. Program always resides in memory. Has direct access to the hardware. Handles file I/O. Manages processes. One copy shared by all users.

10. UNIX Architecture: The Shell Everyone has a login id/ password assigned by an administrator. After the user logs in, a shell program is invoked. The shell accepts user input, options, and parameters. The shell makes calls to the kernel to execute the user request. At least one shell is invoked by every user. User has a choice of shells: Bourne, C, Korn, Secure, Bash, …

11. A Typical UNIX Session