1. Operating Systems Salihu Ibrahim Dasuki (PhD) CSC102 INTRODUCTION TO COMPUTER SCIENCE

2.  Aim ◦ Introduce the concepts of operating systems  Purpose ◦ To understand how the resources within a computer, including processor, memory, peripherals and user interfaces, are managed CSC102 INTRODUCTION TO COMPUTER SCIENCE

3.  Early computers could execute only one program, one job, at a time: ◦ The programmer gave the job to the operator ◦ The operator entered the job into the computer ◦ The operating system executed the job ◦ The operator gave the output to the programmer CSC102 INTRODUCTION TO COMPUTER SCIENCE

4.  Later, a set of jobs could be entered onto the computer at the same time  The jobs were held in a queue  The operating system took the jobs off the queue, one at a time, and executed them  Less human intervention CSC102 INTRODUCTION TO COMPUTER SCIENCE

6.  A drawback of batch processing: ◦ the user cannot interact with the program ◦ important for word processing, airline reservations, game playing, and other applications  New operating systems were developed to enable the user to carry on a dialogue with the program via a remote terminal CSC102 INTRODUCTION TO COMPUTER SCIENCE

8.  A single user could interact with the computer via newer interactive operating systems CSC102 INTRODUCTION TO COMPUTER SCIENCE

9.  Later operating systems sought to allow multiple users to access the same computer simultaneously ◦ The operating system needs to share the computer resources between users/jobs  To handle this, these operating systems use multiprogramming CSC102 INTRODUCTION TO COMPUTER SCIENCE

10.  In multiprogramming, time is divided into intervals  Each program is restricted to execute in only one interval at a time  When all have executed (partially), the procedure is repeated  The illusion is given that the programs are executing simultaneously CSC102 INTRODUCTION TO COMPUTER SCIENCE

11.  Multiple users could now interact with different programs running on the same computer CSC102 INTRODUCTION TO COMPUTER SCIENCE

12. Subsequent to this, multitasking operating systems were developed – each user can execute multiple programs at the same time CSC102 INTRODUCTION TO COMPUTER SCIENCE

13.  How does Operating System compare with other computer software?  Computer software comprise application and system software  System software comprises utility software and the operating system ◦ Utility software supports the operating system  The operating system comprises the user interface and the kernel CSC102 INTRODUCTION TO COMPUTER SCIENCE

15.  The user interface supports communication with the user  Older interfaces were text-based, keyboard entry  Newer interfaces are graphical user interfaces, including point and click, touch screens, game consoles, and more CSC102 INTRODUCTION TO COMPUTER SCIENCE

16.  The window manager is responsible for managing application windows displayed on the computer screen  Applications get access to the screen via requests to the window manager  The window manager intercepts user input, passing information back to the application ◦ E.g. the position and movement of the mouse CSC102 INTRODUCTION TO COMPUTER SCIENCE

17.  The kernel is the core of an operating system.  The components of the kernel are: ◦ File Manager ◦ Memory Manager ◦ Scheduler ◦ Dispatcher ◦ Device Drivers CSC102 INTRODUCTION TO COMPUTER SCIENCE

18.  Coordinates the use of the computer’s mass storage – i.e. hard disks  Maintains records of all files – these are retrieved from the mass storage device, and updated when necessary  Allows files to be organized into directories; directories can contain sub-directories  Controls the access to files by “application software” CSC102 INTRODUCTION TO COMPUTER SCIENCE

19.  Coordinates the use of main memory  Finds and allocates memory space for programs and data – remember, multiple users, multiple programs  Keeps track of memory no longer being used  If main memory exceeded, it uses mass storage CSC102 INTRODUCTION TO COMPUTER SCIENCE

20.  A program that is executing on a computer is called a process  The scheduler maintains a record of all processes, in the process table  It introduces new processes, adding an entry in the process table  And it removes completed processes, removing their entry from the process table CSC102 INTRODUCTION TO COMPUTER SCIENCE

21.  The dispatcher oversees the execution of processes  It accomplishes this using multiprogramming: ◦ Dividing time into short segments called time slices ◦ Switching the processes in and out so each is allowed to execute for one time slice CSC102 INTRODUCTION TO COMPUTER SCIENCE

22.  Device drivers are programs that communicate with the controllers that control peripheral devices ◦ E.g. Printers, disk drives, monitors  The device driver is installed when the peripheral device is added to the computer system ◦ It may be downloaded from the Internet CSC102 INTRODUCTION TO COMPUTER SCIENCE

23.  Operating systems are the cornerstone of computer systems  They come in many forms: Microsoft Windows 7, Linux, Unix, Mac OS, etc.  With many different user interfaces  But all share important features in common CSC102 INTRODUCTION TO COMPUTER SCIENCE

24.  What are the names of operating systems used in mobile phones?  What is a smartphone?  What is the Samsung Galaxy Note? Why is it distinct from the standard smartphone? Have any other phones displayed this uniqueness  What is the Cloud? What is Cloud Computing?  Is a laptop a multiprogramming or a multitasking system, or both?  Due Date: 12/09/2015 CSC102 INTRODUCTION TO COMPUTER SCIENCE