OS Lecture 1 Notes : unacademy computer science

 Operating System Lecture 1 Notes



video link : https://youtu.be/By6lWjiPpVI

A. Operating system :

1. it shows us beautiful view of ugly hardware.
 2. interface between user and hardware.
 3. it provides us API's. Set of utilities to simplify application
 development/execution.
 4. Acts like a government
 5. it is a computer program that organizes a number of other programs at the
 same time

➖➖➖

B. Services of O.S


1. Program execution ( the most imp part of os )
 2. user interface
 3. I/O operation
 4. file system manipulation
 5. Communication ( inter process communication : app to app communication )
 6. Error Detection
 7. Resource Allocation ( loading in ram , etc )
 8. Accounting ( we can see in task manager )
9. Protection and Security

➖➖➖


C. Goals of operating system

1. Convenience ( User-friendly )
 2. Efficiency
3. Portability ( OS which can work on other hardware)
 4. Reliability
 5. Scalability ( the ability to install new update without deleting previous one )
 6. Robustness ( ability of a computer system to cope with errors during execution)

➖➖➖

D. Parts of Operating System

1. kernel :
connects the system hardware to the application software. it has all the functionalities of OS.
 2. Shell :
It is used to access (kernel's) OS functionalities. It is an Interface GUI , CLI.

➖➖➖

E. System Call

1. It is a way for programs to interact with the OS
 2. simple def : Calling the system function is system call

➖➖➖

F . Dual Mode of Operation :

used to implement protection.
2 Modes :
1. User Mode ( mode bit = 1 )
2. Kernel / System / Supervisor / Privileged Mode ( mode bit = 0 ) : in this mode - Privileged instruction are executed







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