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

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

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. 2012 Kay A. Robbins, Steven Robbins, Unix Systems Programming, 2003 Recommended Reference Books: Herbert Schildt. Windows 95 Programming in C and C++. 1995 Herbert Schildt. Windows 2000 Programming from the Ground Up. 2000.

Handout Content: 1.1. What is an Operating System 1.2. Computer system types and description 1.2.1. Mainframe Computer Systems 1.2.1.1. Batch Systems 1.2.1.2. Multiprogrammed Systems 1.2.1.3. Time Sharing Systems 1.2.2. Desktop Systems 1.2.3. Multiprocessor Systems Tandem, Symmetric, Asymmetric multiprocessor systems 1.2.4. Distributed Systems 1.2.4.1. Client Server Systems 1.2.4.2. Peer-to-Peer Systems 1.2.5. Clustered Systems 1.2.6. Real Time Systems 1.2.7. Handheld Systems Textbook - Silberschatz, Chapter 1

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

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.

What is an Operating System ?

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.

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.

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.

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

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 (15+11+5)/3 =10.3 8/15 ~53%

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.

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

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 (15+11+5)/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%

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.

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%

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 (15+11+5)/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%