Department of Computer Science Operating Systems OPS621S Semester 2

Course Coordinator Mr. Nasimane Ekandjo Department of Computer Science IT House, 5 Storch Phone: (office) address: Consultation: Appointment via  Please do not come give me excuses that you did not find me in the office. Send me an !

Venues Full Time Lectures: Monday (09:30) Lecture venue : Aud. 3 Laboratories: Monday (15:00), Thursday (09:30) Friday (07:30) Lab venue: Office Building, SIT Labs Part Time Lectures: Monday (17:15) Lecture venue : Room 212 Laboratories: Wednesday (18:35) Lab venue : Office Building, SIT Labs 3

Course Overview  Broad understanding and knowledge of operating systems  Examine the way operating system works  Detailed functions of operating systems  Various operating systems and their functions  Algorithms and policies used in operating systems

How this course is taught  The course covers 120 Notional hours –Theory lecture (15 hours) –Guided Practical tutorials (30 hours) –Self study and Assessments (75 hours)  The course is offered in blended e–learning mode. The e–learning part is on: –1) Submit your exercises –2) Write a test (probably) –3) Download course outline, slides, further material –4) Discuss subject questions

What to do in order to pass  Always attend theory lectures  Always attend laboratories & self studies  Make use of the Self Studies & tutorials  Complete all homework and exercises  Utilize your notional hours  Use APA Referencing / Citing Guide for your assignments / case studies

Let the business begin!

Lecture Objectives  What is an operating system  Computer system components  Types of computer programs  Components of operating system Memory Processor Device File  Types of operating systems  Features of operating systems  Homework

What is an Operating System?  Computer system: –Hardware (tangible machine/electronic components) –System programs (software) –Application programs  Operating system: –Chief software componet –Part of computer system –Manages all hardware and software –Acts as an interface between user and system –Organised set of programs –Schedule tasks and it manage storage –Control and manage computer resources –Making computer system convenient to use in effective manner.

Components of Operating System 1.Hardware – provides basic computing resources (CPU, memory, I/O devices). 2.Operating system – controls and coordinates the use of the hardware among the various application programs for the various users. 3.Applications programs – define the ways in which the system resources are used to solve the computing problems of the users (compilers, database systems, video games, business programs). 4.Users (people, machines, other computers).

Three types of program  User / application program –Programs used by users to perform tasks  System program –Interface between user and computer  Driver program –Communicate I/O device with the computer

Four sub-system managers of OS  Memory manager  Processor manager  Device manager  File manager  “Network manager”

Four sub-system managers of OS (cont.) (figure 1.1) This pyramid represents an operating system on a stand-alone computer unconnected to a network. It shows the four subsystem managers and the user interface. © Cengage Learning 2014

User Command Interface  Provides user communication –User issues commands to operating system  Unique to each operating system –May vary between versions  Essential managers provide support  Two primary types: o Graphical User Interface (GUI) o Command Line Interface

Subsystems must work with each other

Operating System Managers  Each manager: –Works closely with other managers –Perform a unique task  Tasks of a Manager: –Monitor its resources continuously –Enforce policies determining: Who gets what, when, and how much –Allocate the resource (when appropriate) –De-allocate the resource (when appropriate)

Network Manager  Coordinates the services required for multiple systems to work cohesively together  Shared network resources: Memory space, processors, printers, databases, applications, etc.

Memory Management In charge of main memory (RAM) Preserving space in main memory occupied by operating system Checking validity and legality of memory space request Allocate memory to processes and de-allocate when they are done Setting up memory tracking table o Tracks usage of memory by sections o Needed in multiuser environment

Processor Management In charge of allocating Central Processing Unit (CPU) Tracks process status A process is a program in execution Handle jobs as they enter the system Handled by Job Scheduler Manages creation and deletion of processes Manage each process within those jobs Handled by Process Scheduler

Device Management In charge of monitoring all resources peripheral devices Devices, channels, and control units Choosing most efficient resource allocation method Printers, ports, disk drives, etc. Based on scheduling policy Allocating and de-allocating devices Consists of policies and procedures for handling I/O devices Accepts input from user and give corresponding output

File Management A file is a collection of related information Manages files stored on disk In charge of tracking every file in the system Data files, program files, compilers, application programs Controlling user/program modification restrictions Read-only, read-write, create, delete Enforcing user/program resource access restrictions Uses predetermined access policies Allocating resources (opening files) and de-allocating (closing files)

Cooperation Issues  No single manager performs tasks in isolation  Each element of an operating system –Performs individual tasks and –Harmoniously interacts with other managers Incredible precision required for operating system to work smoothly More complicated when networking is involved

Cloud Computing  Practice of using Internet-connected resources –Performing processing, storage, or other operations  Operating system maintains responsibility –Managing all local resources and coordinating data transfer to and from the cloud  Role of the operating system –Accessing resources –Managing the system efficiently

Types of Operating System Batch processing Time-sharing Hybrid OS Real time OS Distributed OS Embedded OS Interactive OS Two distinguishing features: o Response time o How data enters into the system Multi-programmingMulti- processingMulti-tasking Read these types on your own!!

Features of Operating System  Multiprocessing –Allows parallel program execution –Two or more CPUs handle jobs  Multitasking –To handle two or more programs at the same time from a user’s perception –CPU can only perform one task at the same time, however, it runs so fast that two or more jobs seems to execute at the same time.  Multiprogramming –Two or more programs stored in main memory at the same time –When one job needs to wait (e.g. I/O operation), CPU will switch to another job to execute –When the first job finishes waiting, CPU will get back to the first job to execute –Efficiently utilize all computing resources

Program, Job, Process and thread  A program is a non-active set of instructions stored on disk.  A program becomes a job from the moment it is selected for execution until it has finished running and becomes a program again.  A process is a program in execution. It is a program that has started but has not finished.  A thread => multiple actions that can be executed at the same time. In other words, a process can be made up of several threads.

Homework  Read history of machine hardware –Memory chips –Input/output devices (monitor, keyboard, printer, etc.) –Storage devices (disks, magnetic tape, card readers, drums, etc.) –Central Processing Unit (Arithmetic Logic Unit, registers, internal control, bus control, etc.)  Read history of operating system development  You are required to make a summary of what you have read and submit it via e-poly. 1-3 pages should be fine. End