1. UNIX Chapter 01 Overview of Operating Systems Mr. Mohammad A. Smirat

2. Introduction Many operating systems are available today. Some of these are general to run on any type of computers. Personal computers to mainframes. Others are designed to run on particular types of computer system. Real time systems (robots).

3. What is an Operating System? UNIX shell, Commands, and application programs Language libraries and system call interface Operating System Kernel Computer Hardware Users AUI API Layered view of a Computer System

4. What is an Operating System? ( cont …) A computer system consists of various software and hardware components. The primary purposes of operating systems is to facilitate easy, efficient, fair, orderly, secure use of these resources.

5. Software components Application Software (for ordinary user). Language libraries, system calls, and program generation tools (for programmers use). AUI is glued to the kernel via the language libraries and the system call interface. System call interface comprises a set of function that can be used by the application and library routines to start execution of the kernel code for a particular service.

6. Hardware Components Keyboard, display screen, … Main memory CPU Disk drive Modem, Ethernet, …

7. Operating System Services Execution of a program Input an output operations performed by programs Communication between processes Error detection an reporting Manipulation of all types of files. Management of users and security.

8. Interfaces Or shells Character versus graphical user interfaces. In GUI systems, users use mainly point and click devices (mouse) for issuing commands to the system. (MacOS, OS/2, MW) In GUI systems, users use mainly a keyboard for issuing commands to the system. (Dos, UNIX) GUI makes a computer easier to use. GUI presents an extra layer which make the computer slower. CUI gives you the control of your computer. CUI is more efficient.

9. Types of Operating System (no. of users and processes) Single user, single process system (for PC) Dos, Windows 3.1, and MacOS. Single user, multi-process system (for PC) OS/2 and Windows NT. Multi-user, multi-process system. UNIX, LINUX and Windows NT server. These systems are used to increase resource utilization by multiplexing expensive resources such as the CPU. (Why?) This will increase the throughput of the system.

10. Types of Operating System (cont…) The mechanism of assigning the CPU to another process when the current process is performing I/O is known as multiprogramming. Operating systems that allow their users to interact with their executing programs are known as interactive operating systems. Others that do not allow are called batch operating systems. The multi-user, multiproces, and interactive operating systems are known as time sharing systems.