Lecture 1-Kernel

Question 1

Whats is a Computer System Structure?

Answer 1

A computer system consists of hardware and software.

Software: application software and system software.

Operating system is the most important system software.

Question 2

What is a Operating system?

Answer 2

A computer program that mediates between hardware and application programs.

Consists of many loosely related parts handling
Memory management
I/O management
CPU Scheduling
Communications?
Multitasking/multiprogramming?

Principles:
Keep user programs from Crashing OS and each other
Allocate resources eciently and fairly

We will study algorithms run by these parts.
Assumption: single-processor computer

Question 3

What is a Network?

Answer 3

A network is two or more computers connected by a physical

medium.

Question 4

Distributed systems?

Answer 4

Distributed system is a program than runs on two or more computers.

We will implement a simple distributed system based on the client-server architecture.

Detailed discussion of the subject is oered by the “Distributed system” module.

Question 5

What is a Interrupt System?

Answer 5

Interrupt is a key technique for OSs
Interrupt alerts the OS when some event occurs, e.g.,
When an I/O occurs, execution of one program is suspended.
CPU could be switched to execute another program.
When the I/O completes, an interrupt will occur, which diverts.
execution to the interrupt handling routine
The suspended program may restart.

Interrupt enables OSs to oversee programs and I/O events simultaneously

Question 6

What are the types of interrupts?

Answer 6

I/O Interrupt: by I/O devices to signal completion or error

Timer: by a clock within the CPU; used to alert the OS at pre-set intervals on time critical activities

Hardware Error: by hardware faults

Program: by error conditions within user programs, e.g., division by zero

Question 7

What is Kernel Mode?

Answer 7

OS needs to protect users from each other for security

If a user had access to all machine instructions, then the user could do anything an OS can

The solution is for the CPU to have a special operating mode, the kernel or supervisor mode, which can only be invoked by the OS

In the kernel mode, OS can execute certain privileged instructions,
e.g., I/O operation and system data modication, which are not available to normal program (user mode)