Important Points to remember for Operating System

Test and Set Operation:

This operation reads the memory block. If the memory is allocated, then it keep the bit 1 otherwise it allocates the memory and set the bit from 0 to 1

It works as TestAndSet(a,b)

1. Read the value of b
2. Value of b goes to a
3. b=True

It can be used for locking and unlocking memory

System Calls: The System Call is the Request for Running any Program and for Performing any Operation on the System. 

Scheduler:

• Long term scheduler: determines which programs should be admitted for execution and when and which ones should be exited
• Middle Term scheduler transfers data from secondary memory to primary memory and vice versa
• Short time scheduler: timely allocates CPU to ready processes.

Fork System Calls: 

• Successful: returns ParentID-> childPID and ChildProcess->0
• Unsuccessful: returns ParentID ->1

Threads: Light weight process because they share code and data. However, every thread have its own register and stack.