Introduction to computer science course Fall_2018

1. +
Dr Ramadan Babers
Faculty of Science - Helwan University
Fall-2018
Introduction
to
Computer
LEC - 6

2. +
Operating Systems
2

3. Chapter 6 Outlines
 Introduction
 What is an Operating System?
 Components of an Operating System
3

4. 1- Introduction
4
Operating system (OS) was just the basic
piece of software that ruled the machine
and allowed it to manipulate files.
The job of the OS is to provide for an
orderly and controlled allocation of the
processors, memories, and I/O devices
among the various programs competing
for them.
Sometimes, OS is defined as an Extended
Machine because it presents to the user an
extended or virtual machine that is easier
to program and hide hardware details
from the programmer.

5. 2- What is an Operating System?
5
The OS separates the users with their
applications from the hardware of the
computer.
Applications programs – define the ways in
which the system resources are used to solve the
computing problems of the users (compilers,
database systems, video games, business
programs).
Users (people, machines, other computers).
The Operating System controls and coordinates
the use of the hardware among the various
application programs for the various users.
Hardware – provides basic computing resources
(CPU, memory, I/O devices).

6. 3- Components of an Operating System
6
The main components of an operating system could be
summarized in:
1) Process Management
2) Memory Management
3) File Management
4) I/O System Management
5) Protection (security) System
6) Networking (Distributed Systems)

7. 3-1 Process Management
7
Process Definition:
is a program in execution;
process execution must
progress in a sequential
fashion. A process may be a
CPU process or an I/O
process.

8. 3-1-1 Process States
8
As a process executes, it changes state as follows (shown in figure)
1. New: The process is being created.
2. Running: Instructions are being executed.
3. Waiting: The process is waiting for some event to occur.
4. Ready: The process is waiting to be assigned to a processor.
5. Terminated: The process has finished execution.

9. 3-2 Memory Management
9
Most computers have a memory
hierarchy with:
1. ROM
is a small amount of memory (in size)
is very fast,
is expensive,
nonvolatile cache memory
2. RAM
Hundreds or thousands of megabytes
medium-speed,
medium–price,
volatile main memory

10. 3-2 Memory Management (Cont.)
10
Most computers have a memory
hierarchy with:
3. Hard Disk HD
Hundreds or thousands of gigabytes
slow,
cheap
nonvolatile disk storage
NB:
Volatile here means that: we lose data if we shut down the device (computer or mobile)
Nonvolatile here means that: we did not lose data if we shut down the device

11. 3-2 Memory Management
11
It is the job of the operating system to coordinate
how these memories are used. The part of the
operating system that manages the memory
hierarchy is called the Memory Manager.