1. Where are being used the OS?
Widespread
Invisible
Windows
Mac OS
Linux OS
Routers, switches, … OS
Basic OS
Android OS OS OS OS OS
Internet of Things
Raspbian OS

2. Operating Systems Introduction
This course structure
Sources:
Yale university
UC Berkeley
JHU
My experience

3. Assignments, Project
Student’s should complete programming assignments on “Unix and Windows Processes &Threads programming on C, C++”
Required Textbook:
Abraham Silberschatz, Galvin, Gagne “Operating System Concepts”, 9th edition
Kay A. Robbins, Steven Robbins, Unix Systems Programming, 2003
Recommended Reference Books:
Herbert Schildt. Windows 95 Programming in C and C
Herbert Schildt. Windows 2000 Programming from the Ground Up

4. Handout Content: 1.1. What is an Operating System
1.2. Computer system types and description
Mainframe Computer Systems
Batch Systems
Multiprogrammed Systems
Time Sharing Systems
Desktop Systems
Multiprocessor Systems
Tandem, Symmetric, Asymmetric multiprocessor systems
Distributed Systems
Client Server Systems
Peer-to-Peer Systems
Clustered Systems
Real Time Systems
Handheld Systems
Textbook - Silberschatz, Chapter 1

5. Operating System Purpose
Run user(s’) program(s)
3 main responsibilities
To provide an environment for a computer user to execute programs on computer hardware in a convenient and efficient manner
(Shells, Windows, Terminals, Executable files concept).
To allocate separate resources (memory, processor, disk space, I/O device usage) of the computer as needed to solve the problem given.
The allocation process should be as fair and efficient as possible.
Control the running programs:
supervision of the execution of user programs to prevent errors and improper use of the computer
protection of OS and programs from user programs
management of the operation and control of I/O devices
device drivers, file systems

6. What is an Operating System ?
a program that manages the computer hardware
acts as an intermediary between the user applications and the computer hardware.
provides certain services to programs and to the users of those programs in order to make their tasks possible and easier.

7. What is an Operating System ?

8. Operating-Systems are improved. The principles remain
IoT - The same evolution?
The newest computers repeat the history of old computers starting from the very simple software and growing to full multiprocessor OS.
All OS solutions invented tens of years ago are applicable for newest computers.

9. Early Computer System and OS types. The trends.
Tasks are collected in queues.
CPU takes and runs the parts of tasks from queue giving equal or appropriate time to each of task in order to serve all tasks from the queue.
CPU switches between queue tasks after equal or predefined intervals of time and usually is never idle.
User interaction with the programs is possible
Tasks are collected in similar tasks’ batches
Next task from batch runs when the previous one is finished fully
CPU is dedicated for one task and is often idle
Tasks are collected in queues (pools)
If CPU is idle it takes another (next or previous unfinished) task’s some part to be busy all the time
CPU switches between tasks (programs) when it is idle and usually is busy all the time.

10. Mainframe Computer Systems
Batch Systems
Disadvantage: In this execution environment, the CPU is often idle. Why ? …
Because the speeds of the mechanical I/O devices are intrinsically slower than are those of electronic devices.

11. System Evaluation Criteria
CPU utilization (maximize – keep the CPU as busy as possible) – the time the CPU is busy during some time period
Throughput (maximize) - # of processes that complete their execution per time unit
Turnaround time (minimize)– amount of time to execute a particular process

12. Batch System Evaluation
Task 1
Sec
CPU time. Calculations. 1
I/O time. Input from the HDD 2
Task 2
Sec
CPU time. Calculations. 2
I/O time. Input from the HDD 1
I/O time. Print on Printer.
Task 3
Sec
CPU time. Calculations. 1
I/O time. Output to HDD. 2
Overall time for all 3 tasks to finish
Throughput
Task1 Turnaround time
Task2 Turnaround time
Taks3 Turnaround time
Average Turnaround time for all tasks
CPU utilization 15
3/15 5 11
( )/3 =10.3
8/15 ~53%

13. Computer System types and description
Mainframe Computer Systems
were very huge and expensive.
The expensive system requires the most effective usage of expensive resources - especially the processor.
That was why the main purpose of the MainFrame OS was to utilize the processor by all means.
Thus appear the Multiprogrammed OS.

14. Computer System types and description
Mainframe Computer Systems
Multiprogrammed Systems
Advantage: Multiprogramming increases CPU utilization by organizing jobs so that the CPU always has one to execute. How ? …
Disadvantage: Multiprogrammed, batched systems provided an environment where the various system resources (for example, CPU, memory, peripheral devices) were utilized effectively, but it did not provide for user interaction with the computer system.
Problems: Job and CPU scheduling, Memory management , different tasks resources protection issues should be taken in account to keep the system effective.
Time

15. MultiProgrammed System Evaluation
Task 1
Sec
CPU time. Calculations. 1
I/O time. Input from the HDD 2
Resource Usage Table
Multiprogrammed System
The resource is dedicated if it’s free
and if there is a request
Overall time for all 3 tasks to finish
Throughput
Task1 Turnaround time
Task2 Turnaround time
Taks3 Turnaround time
Average Turnaround time for all tasks
CPU utilization 15
3/15 5 11
( )/3 =10.3
8/15 ~53%
Task 2
Sec
CPU time. Calculations. 2
I/O time. Input from the HDD 1
I/O time. Print on Printer.
Seconds
CPU
HDD
Printer
CPU queue 1 T1
T2,T3 2 T2 T3 3 4 5 6 7 8 9 10
Task 3
Sec
CPU time. Calculations. 1
I/O time. Output to HDD. 2
Overall time for all 3 tasks to finish
Throughput
Task1 Turnaround time
Task2 Turnaround time
Task3 Turnaround time
Average Turnaround time for all tasks
CPU utilization 9
3/9 6 8
(6+9+8)/3=7.67
8/9~89%

16. Multitasking (time sharing) Systems
The CPU executes multiple jobs by switching among them, but the switches occur so frequently that the users can interact with each program while it is running.
Advantage: Users can interact with each program while it is running. How ? …
Time
Disadvantage: Time-sharing operating systems are even more complex (difficult, expensive) than multiprogrammed operating systems.
Problems: Job and CPU scheduling, Memory management, User and Security management, Protection issues should be taken in account to keep the system effective.

17. Time Sharing System Evaluation
For external devices if the task takes the resource it keeps the resource until completing the operation with it.
Task 1
Sec
CPU time. Calculations. 1
I/O time. Input from the HDD 2
Resource Usage Table
Seconds
CPU
HDD
Printer
CPU queue
HDD queue 1 T1
T2,T3 2 T2 T3 3 4 5 6 7 8 9 10
Task 2
Sec
CPU time. Calculations. 2
I/O time. Input from the HDD 1
I/O time. Print on Printer.
Task 3
Sec
CPU time. Calculations. 1
I/O time. Output to HDD. 2
Overall time for all 3 tasks to finish
Throughput
Task1 Turnaround time
Task2 Turnaround time
Task3 Turnaround time
Average Turnaround time for all tasks
CPU utilization 10
3/10 7 6
(7+10+6)/3 =7.67
8/10 ~80%

18. Evaluation of the systems by Criteria
Seconds
CPU
HDD
Printer
CPU queue 1 T1
T2,T3 2 T2 T3 3 4 5 6 7 8 9
Task 1
Sec
CPU time. Calculations. 1
I/O time. Input from the HDD 2
Seconds
CPU
HDD
Printer 1 T1 2 3 4 5 6 T2 7 8 9 10 11 12 T3 13 14 15
Task 2
Sec
CPU time. Calculations. 2
I/O time. Input from the HDD 1
I/O time. Print on Printer.
Seconds
CPU
HDD
Printer
CPU queue
HDD queue 1 T1
T2,T3 2 T2 T3 3 4 5 6 7 8 9 10
Task 3
Sec
CPU time. Calculations. 1
I/O time. Output to HDD. 2
Overall time for all 3 tasks to finish
Throughput
Task1 Turnaround time
Task2 Turnaround time
Task3 Turnaround time
Average Turnaround time for all tasks
CPU utilization
Batch 15
3/15 5 11
( )/3=10.3
8/15 ~53%
Multiprogrammed 9
3/9 6 8
(6+9+8)/3=7.67
8/9~89%
Time Sharing 10
3/10 7
(7+10+6)/3=7.67
8/10~80%