Slides detailing about the structure of an operating system.

1. OS STRUCTURE

2. Things we should know,
Before we start :
1. What is an Operating System?
2. Why do we need it ?

3. What is an Operating System ?
1.A programt hat manages a comput er
s ys t ems hardware.
2.An envi ronment / f oundat i on f or
appl i cat i on programs t o run on.
3.A bri dge t hat enabl es eas y connect i ons
bet ween comput er hardware and us er.
Mai n Goal : To be Conveni ent and Ef f i ci ent
t o us e.

4. Why Do We Need an Operat i ng
Syst em ?
-> To conveniently and efficiently utilize the resources that the
computer provides us. To dig it out all.
-> Without an OS it would be time consuming as well as a mental
harassment for the user to get the computer to complete a task.

5. OS StructureOS Structure
Multiprogramming:Multiprogramming:
Loopholes in Multiprogramming Systems:Loopholes in Multiprogramming Systems:
Several processes are kept on the disk (job pool) awaiting memory allocation. TheSeveral processes are kept on the disk (job pool) awaiting memory allocation. The
OS picks and starts executing processes. If a process needs to wait i.e. I/O operation, then,OS picks and starts executing processes. If a process needs to wait i.e. I/O operation, then,
instead of letting CPU to be idle the OS switches to the execution of another process, andinstead of letting CPU to be idle the OS switches to the execution of another process, and
so on.so on.
If an earlier process has finished waiting, then that process gets back the main memoryIf an earlier process has finished waiting, then that process gets back the main memory
again. Therefore, the CPU does not remain idle until and unless no processes are left foragain. Therefore, the CPU does not remain idle until and unless no processes are left for
execution.execution.
•Does not provide user interaction with the computer system.Does not provide user interaction with the computer system.

6. Time Sharing/Multitasking
Systems
 CPU executes multiple job by frequently switching among them so that the
user can interact with each program.
 The system should be interactive so that the user can give instructions to the
process directly and wait for immediate result, with a very short response
time.
 The privilege of TSOS is that it can provide many users to work on the
system simultaneously with their processes running as if they were the only
one using the system.
 Only a small amount of CPU time is needed for each user.

7. Operating System Structure
• Monolithic Systems (Simple Structure)
• Layered Structure
• Microkernel System

8. Monolithic OS Structure
• These are the earliest operating system structuresThese are the earliest operating system structures
which had to manage very few peripherals.which had to manage very few peripherals.
• All the components of the OS were integrated under aAll the components of the OS were integrated under a
single unit Kernel address.single unit Kernel address.
• Programs and data were stored in the memory.Programs and data were stored in the memory.
• This type of structure was used in few popularThis type of structure was used in few popular
Operating Systems like OS/360, VMS and Linux.Operating Systems like OS/360, VMS and Linux.

10. Layered Structure
1. In this approach the OS consists of several layers where each layer has a well defined
functionality, And can be altered and tested independently.
2. These are arranged in ascending order of abstraction, the lowest layer deals with the
hardware and the topmost layer provides an interface to the application program and user
process.
3. Each layer relies on the services of the underlying layer. The communication takes place
only between adjacent layers.
Which one
do I have ?

12. Microkernel Structure
1. Designed to solve the lacking of Monolithic Kernel.
2. Microkernel architecture provides the abstraction for complete
OS designing and implementation along with minimum
functionalities residing in the kernel.
3. Most of the functionalities are executed from separate server.
Which occupies separate memory space.
4. The user process acts as a client.
5. The microkernel uses IPC (inter process communication) to
send request to a specific server.

13. Hardware

14. Do you still have a question ?
Okay then ! Go for it.