Download 1.1. OS Introduction Operating System Types

Operating System Principles
AUA CIS331
Albert Minasyan
Operating Systems Principles (Introduction)
The purpose of the operating system is to run the user program on the computer.
Nowadays everywhere are being used different types of computers for different purposes. All they
need operating systems to perform their tasks.
Starting from very small computers inside the handheld devices and finishing with huge
supercomputers in data centers have their operating systems. But surprisingly all those different
operating systems have the same basic principles.
This course describes that basic principles and allows to understand the differences between the
operating systems and the reasons why this or that operating system is being used on different
computers or computer systems.
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Operating System Principles
AUA CIS331
Albert Minasyan
Sources:
•
•
•
•
This course structure
OS Introduction
Processes, Threads,
Scheduling, Synchronization
Memory management
I/O systems
Interrupts
Operating
Systems
Yale university
UC Berkeley
JHU
My experience
File Systems
Protection and Security
Distributed Processing
Networks
Different OS comparison
Exercises, Assignments, Project (C, C++)
WinAPI
Linux API
Windows OS
Real
Workstation
Linux OS
Virtual
Machine
Student’s should complete programming assignments on “Unix and Windows Processes and Threads
programming on C, C++”
Required Textbook:
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.
 Kate Gregory. Using Visual C++ 6.
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Operating System Principles
AUA CIS331
Albert Minasyan
Goal of this handout: to teach the differences of main types of OS and the evaluation criteria of OS.
Outcome: Students should distinguish the different types of OS/computer systems and be able to apply the
evaluation criteria to different types of OS and evaluate different systems’ performance.
Handout Content:
 1.1. What is an Operating System
 1.2. Computer system types and description
o 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
o 1.2.2. Desktop Systems
o 1.2.3. Multiprocessor Systems
 Tandem, Symmetric, Asymmetric multiprocessor systems
o 1.2.4. Distributed Systems
 1.2.4.1. Client Server Systems
 1.2.4.2. Peer-to-Peer Systems
o 1.2.5. Clustered Systems
o 1.2.6. Real Time Systems
o 1.2.7. Handheld Systems
Textbook Silberschatz, Chapter 1
1.1. What is an Operating System
The purpose of the operating system is to run the user program(s).
The three main responsibilities of an operating system:
 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 the 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.
 As a control program it serves two major functions:
o supervision of the execution of user programs to prevent errors and improper use of
the computer (protection of OS and programs from user programs).
o management of the operation and control of I/O devices (device drivers, file systems)

An operating system is a program that manages the computer hardware and acts as an
intermediary between the user applications and the computer hardware.
The operating system must ensure the correct operation of the computer system. To prevent user
programs from interfering with the proper operation of the system, the hardware must provide
appropriate mechanisms.
The operating system provides certain services to programs and to the users of those programs in
order to make their tasks possible and easier.
The services differ from one operating system to another, but we identify and explore some common
classes of these services.
An operating system is an important part of almost every computer system. A computer system can be
divided roughly into four components: the hardware, the operating system, the application
programs, and the users.
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Operating System Principles
AUA CIS331
User 1
Albert Minasyan
User 2
Compiler
Assembler
User 3
User n
Text editor
Database System
System and application programs
Operating System
Computer Hardware
Abstract view of the components of a computer system.
The hardware - the central processing unit (CPU), the memory, and the input/output (I/O) devices provides the basic computing resources.
The application programs-such as word processors, spreadsheets, compilers, and web browsers define the ways in which these resources are used to solve the computing problems of the users.
The operating system controls and coordinates the use of the hardware among the various application
programs for the various users.
The operating system provides the means for the proper use of the resources of the computer system.
User Application
Programs
Trying to use Computing
Resources
Using ready solutions is
possible (is effective)
API to OS for User
Applications
Operating System
Device drivers
Direct usage is possible (but
is not effective)
Control API to Hardware
Computing
Resources
are provided by
Computer Hardware
(CPU, Memory, I/O
devices)
An application programming interface (API) is a set of functions, procedures, methods or classes that
an operating system, library or service provides to support requests made by computer programs.
The operating system is similar to a government. Like a government, it performs no useful function
by itself. It simply provides an environment within which other programs can do useful work.
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Operating System Principles
AUA CIS331
Albert Minasyan
1.2. Computer System types and description
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.
1.2.1. Mainframe Computer Systems
Mainframe computer systems were the first computers used to tackle many commercial and scientific
applications. They grew of from simple batch systems, where the computer runs one - and only oneapplication, to time-shared systems, which allow for user interaction with the computer system.
Mainframe Computer
Systems
Desktop Computer
Systems
Operating Systems
Batch Systems
Multiprogrammed
Systems
Time Sharing
Systems
 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.
 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
OS improves
 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
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Operating System Principles
AUA CIS331
Albert Minasyan
1.2.1.1 Batch Systems
Early computers were physically enormous machines run from a console. The common input devices
were card readers and tape drives. The common output devices were line printers, tape drives, and
card punches.
Batch of Tasks (Jobs)
CPU
Input
Task #1
Input
Calculation
Output
Save Result
Task #2
Input
Calculation
Output
Save Result
Task #3
Read
Calculation
Output
Save Result
Output
Read
Save
Disks
Tapes
The user did not interact directly with the computer systems. Rather, the user
prepared a job-which consisted of the program, the data, and some control
information about the nature of the job (control cards)-and submitted it to the
computer operator. The job was usually in the form of punch cards. At some
later time (after minutes, hours, or days), the output appeared. The output
consisted of the result of the program, as well as a dump of the final memory
and register contents for debugging.
The operating system in these early computers was fairly simple. Its major
task was to transfer control automatically from one job to the next. The
operating system was always resident in memory.
To speed up processing, operators batched together jobs with similar needs
and ran them through the computer as a group.
Memory layout for
batch system
Disadvantage: In this execution environment, the CPU is often idle, because the speeds of the
mechanical I/O devices are intrinsically slower than are those of electronic devices.
Even a slow CPU works in the microsecond range, with thousands of instructions executed per
second. A fast card reader, on the other hand, might read 1200 cards per minute (or 20 cards per
second). Thus, the difference in speed between the CPU and its I/O devices may be three orders of
magnitude or more.
Over time, of course, improvements in technology and the introduction of disks resulted in
faster I/O devices. However, CPU speeds increased to an even greater extent, so the problem was
not only unresolved, but exacerbated.
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Operating System Principles
AUA CIS331
Albert Minasyan
1.2.1.2 Multiprogrammed Systems




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.
The most important aspect of job scheduling is the ability to multiprogram. A single user cannot, in
general, keep either the CPU or the I/O devices busy at all times.
Advantage: Multiprogramming increases CPU utilization by organizing jobs so that the CPU
always has one to execute.
CPU Scheduling
Task #1
CPU
Input
Read
Calculation
Output
Output
Read
Task #2
Jobs in
memory
Input
Calculation
Output
Save
W
Disks
Tapes
Task #3
Job Scheduling
Read Wait
Calculation
Output
W
Job pool
on Disk
Memory management
Resource Protection
The idea is as follows: The operating system keeps several jobs in
memory simultaneously. This set of jobs is a subset of the jobs kept in
the job pool-since the number of jobs that can be kept simultaneously
in memory is usually much smaller than the number of jobs that can be
in the job pool.
The operating system picks and begins to execute one of the jobs in the
memory. Eventually, the job may have to wait for some task, such as
an I/O operation, to complete.
In a non-multiprogrammed system, the CPU would sit idle.
In a multiprogramming system, the operating system simply switches
to, and executes, another job.
When that job needs to wait, the CPU is switched to another job, and
so on. Eventually, the first job finishes waiting and gets the CPU back.
As long as at least one job needs to execute, the CPU is never idle.
Memory layout for
multiprogramming system
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Operating System Principles
AUA CIS331
Albert Minasyan
Multiprogramming is the first instance where the operating system must make decisions for the users.
Multiprogrammed operating systems are therefore fairly sophisticated. All the jobs that enter the
system are kept in the job pool. This pool consists of all processes residing on disk awaiting allocation
of main memory. If several jobs are ready to be brought into memory, and if there is not enough room
for all of them, then the system must choose among them. Making this decision is job scheduling,
which is discussed later.
When the operating system selects a job from the job pool, it loads that job into memory for
execution. Having several programs in memory at the same time requires some form of memory
management.
In addition, if several jobs are ready to run at the same time, the system must choose among them.
Making this decision is CPU scheduling.
Finally, multiple jobs running concurrently require that their ability to affect one another be limited in
all phases of the operating system, including process scheduling, disk storage, and memory
management.
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.
1.2.1.3. Time Sharing Systems
Time sharing (or multitasking) is a logical extension of multiprogramming.
Advantage: 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.
Processes in Physical Memory
CPU
Process #1
Input
Calculation
Input
Output
Calculation
Output
Save Result
CPU time sharing
Process concurrent execution
Input
Process #2
Input
Calculation
Output
Save Result
Output
Process #3
Read
Calculation
Output
Physical
Save Result
Memory
Read
Save
Disks
File system
Users
Security
Memory management
and protection
Paging
Virtual
Memory
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Operating System Principles
AUA CIS331
Albert Minasyan
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.
An interactive (or hands-on) computer system provides direct communication between the user and
the system. The user gives instructions to the operating system or to a program directly, using a
keyboard or a mouse, and waits for immediate results. Accordingly, the response time should be short
typically within 1 second or so.
A time-shared operating system allows many users to share the computer simultaneously. Since each
action or command in a time-shared system tends to be short, only a little CPU time is needed
for each user. As the system switches rapidly from one user to the next, each user is given the
impression that the entire computer system is dedicated to her use, even though it is being shared
among many users.
A time-shared operating system uses CPU scheduling and multiprogramming to provide each user
with a small portion of a time-shared computer.
Each user has at least one separate program in memory. A program loaded into memory and executing
is commonly referred to as a process. When a process executes, it typically executes for only a short
time before it either finishes or needs to perform I/O. I/O may be interactive; that is, output is to a
display for the user and input is from a user keyboard, mouse, or other device. Since interactive I/O
typically runs at "people speeds," it may take a long time to complete. Input, for example, may be
bounded by the user's typing speed; seven characters per second is fast for people, but incredibly slow
for computers.
Rather than let the CPU sit idle when this interactive input takes place, the operating system will
rapidly switch the CPU to the program of some other user.
In both, several jobs must be kept simultaneously in memory, so the system must have memory
management and protection.
To obtain a reasonable response time, jobs may have to be swapped in and out of main memory to the
disk that now serves as a backing store for main memory. A common method for achieving this goal
is virtual memory, which is a technique that allows the execution of a job that may not be completely
in memory. The main advantage of the virtual-memory scheme is that programs can be larger than
physical memory. Further, it abstracts main memory into a large, uniform array of storage,
separating logical memory as viewed by the user from physical memory. This arrangement frees
programmers from concern over memory-storage limitations.
Time-sharing systems must also provide a file system (as should be done by any OS). The file system
resides on a collection of disks; hence, disk management must be provided. Also, time-sharing
systems provide a mechanism for concurrent execution, which requires sophisticated CPU-scheduling
schemes. To ensure orderly execution, the system must provide mechanisms for job synchronization
and communication, and it may ensure that jobs do not get stuck in a deadlock, forever waiting for one
another.
The idea of time sharing was demonstrated as early as 1960, but since time-shared systems are
difficult and expensive to build, they did not become common until the early 1970s. Although some
batch processing is still done, most systems today are time sharing. Accordingly, multiprogramming
and time sharing are the central themes of modern operating systems, and they are the central themes
of this course.
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Operating System Principles
AUA CIS331
Albert Minasyan
System Evaluation Criteria
CPU utilization (maximize) – keep the CPU as busy as possible
Throughput (maximize) - # of processes that complete their execution per time unit
Turnaround time (minimize)– amount of time to execute a particular process



CPU utilization: the time the CPU is busy during some time period. We want to keep the CPU as
busy as possible. CPU utilization may range from 0 to 100 percent. In a real system, it should
range from 40 percent (for a lightly loaded system) to 90 percent (for a heavily used system).
Throughput: If the CPU is busy executing processes, then work is being done. One measure of
work is the number of processes completed per time unit, called throughput. For long processes,
this rate may be 1 process per hour; for short transactions, throughput might be 10 processes per
second.
Turnaround time: From the point of view of a particular process, the important criterion is how
long it takes to execute that process. The interval from the time of submission of a process to the
time of completion is the turnaround time. Turnaround time is the sum of the periods spent
waiting to get into memory, waiting in the ready queue, executing on the CPU, and doing I/O.
Task 1
Resource Usage Table
Batch System
Seconds
CPU
HDD
Prin
ter
1 T1
2
T1
3
T1
4 T1
5 T1
6 T2
7 T2
8
T2
9 T2
10
T2
11
T2
12 T3
13
T3
14
T3
15 T3
Sec
CPU time. Calculations.
I/O time. Input from the HDD
CPU time. Calculations.
1
2
2
Task 2
Sec
CPU time. Calculations.
I/O time. Input from the HDD
CPU time. Calculations.
I/O time. Print on Printer.
2
1
1
2
Task 3
Sec
CPU time. Calculations.
I/O time. Output to HDD.
CPU time. Calculations.
1
2
1
Resource Usage Table
Time Sharing System
For external devices if the task takes the resource it keeps
the resource until completing the operation with it.
Seconds
1
2
3
4
5
6
7
8
9
10
CPU
T1
T2
T3
T2
T1
T3
T1
T2
HDD
CPU
queue
T2,T3
T2,T3
T2,T3
T2,T3
T2,T3
T3
T3
T3
T3
T3
T3
Printer
T1
T1
T3
T3
T2
CPU
queue
T2,T3
T3
T2
T1
HDD
queue
T2
T1
T2
T2
T2
Resource Usage Table
Multiprogrammed System
The resource is dedicated if it’s free
and if there is a request
Seconds
CPU
HDD
Printer
CPU
queue
T2,T3
1 T1
T1
T3
2 T2
T1
T3
3 T2
T2
T1
4 T3
T3
T2
5 T1
T3
T2
6 T1
T3
7 T2
T2
8 T3
T2
9
10
10
Operating System Principles
AUA CIS331
Batch
Multiprogr
ammed
Time
Sharing
Albert Minasyan
Overall time
for all 3 tasks
to finish
15
9
Throu
ghput
Task2
Turnaround
time
11
9
Task3
Turnaround
time
15
8
Average
Turnaround time
for all tasks
(15+11+5)/3=10.3
(6+9+8)/3=7.67
CPU
utilization
3/15
3/9
Task1
Turnaround
time
5
6
10
3/10
7
10
6
(7+10+6)/3=7.67
8/10~80%
8/15 ~53%
8/9~89%
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