1 Sec (3.2) Operating System Architecture OS

2 Software dividing into two categories: 1. Application software 2. System Software  Operating System  Translators Application software: Consists of programs for performing tasks particular to machine's utilization System Software: Performs those tasks that are commonly to computer systems in general

3 Components of Operating System: 1. An operating system must be able to communicate with users, the portion of operating system that handles this communicate is called Shell = Graphical User Interface (GUI) Shell is the interface between a user and the real heart of the OS An important component within the GUI shells is Window Manager Which allocates block of space on the screen, call windows and keeps track of which application is associated with each window

4 Shell = Graphical User Interface (GUI)

5 2) The other component of OS is called Kernel: which contains those software components that perform the very basic functions required by the computer installation. The components of kernel is : 1. File Manager 2. Device drivers 3. Memory Manager 4. Scheduler 5. Dispatcher

6 1) File manager: Whose job is to coordinate the use of the machine's mass storage facilities.  The file manager maintains records of all the files stored in mass storage, including where each file is located, which users are allowed to access the various files and which portion of mass storage are available for new files or extensions to existing files.  Those records are kept on the individual storage medium containing the related files

7 1) File manager:  So is placed on-line for each time, the file manager can retrieve them and thus know what is stored in that particular medium  File managers allow files to be grouped into a bundle called directory or folder  Directory path: a chain of directions within directions  File descriptor: if the file manager approves the requested access, it provides the information needed to find and manipulate the file. this information is stored an area of main memory called file descriptor

8 2) Device Drivers: The another component of kernel, which are the software units that communicates with the controllers to carry out operations on the peripheral devices attached to the machine. Each device driver is uniquely designed for its particular type of device (printer, disk drive, monitor) and translate generic requests into the more technical steps required by the device assigned to that driver.

9 3) Memory Manager:  Which is charged with the task of coordinating the machine's use of main memory  Such duties are minimal in an environment in which a computer is asked to perform only one task at a time  In these cases, the program for performing the current task is placed at a predetermined location in main memory, executed and then replaced by the program for performing the next task

10 3) Memory Manager: In multi-user or multitasking environments in which the computer is asked to address many needs at the same time  The duties of the memory manager are extensive.  In these cases, many programs and blocks of data must reside in main memory concurrently.  Thus, the memory manager must find and assign memory space for these needs and ensure that the actions of each program are restricted to the program's allocated space.

11 3) Memory Manager:  Moreover, as the needs of different activities comes and go, the memory manager must keep track of those memory areas no longer occupied  The task of the memory manager is complicated further when total main memory space required exceeds the space actually available in the computer.

12 3) Memory Manager:  In this case the memory manager may create the illusion of additional memory space by rotating programs and data backs and forth between main memory and mass storage (a technique called paging)  Virtual memory: the large memory space created by the paging

13 Time sharing: Which is the technique of dividing time into intervals and then restricting the execution of a job to only one interval at a time. At the end of each interval, the current job is temporarily set aside and another is allowed to execute during the next interval by rabidly shuffling. The jobs executing simultaneously is crated Time-sharing is used in single-user as well as multi-user

14 Time-sharing between process A and process B

15 Continue: Multitasking = multiprogramming: Using the idea of time share in single user to execute multi program Multi-user: It is to make user feel that he is the only user. This system is to some how serve several users simultaneously. this happens by specifying a time slice which according to it the user is served and then switched to another user till the user is finished.

16 4) + 5) Scheduler and Dispatcher : Scheduler : determines which activities are to be considered for execution (in time-sharing system) Dispatcher : controls the allocation of time to these activities

17 Booting process: The program stored in ROM called Bootstrap

18 The booting process: