1.5 Operating-System Operations

--Modern OS is interrupt driven.


1.5.1 Dual-Mode Operation

--To ensure the proper execution of the OS,the OS code and the user’s code must be distinguished.


--User Mode and Kernel Mode.


--At system boot time, the hardware startsin kernel mode.


--Whenever the OS gains control of thecomputer, it is in the kernel mode.


--It protects the OS from errant users.


--The privileged instructions only executedin kernel mode.


--Switch between user mode and kernel modevia aninterrupt, a trap, or a system call.


1.5.2 Timer

--A timer can be set to interrupt thecomputer after a specified period.


--We can use the timer to prevent a userprogram from running too long.


1.6 Process Management

--Process is an active entity.


--activities:
Scheduling processes andthreads on the CPUs.

Creating and deleting bothuser and system processes.

Suspending and resumingprocesses.

Synchronization andCommunicating.


1.7 Memory Management

--activities
Keeping track of which partsof memory being used and by whom.


Deciding whichprocess and data to move in and out of memory.


A and D memoryspaces.