This document contains the syllabus and topics covered in Lecture 6 of an Operating Systems course. It discusses different operating system structures including simple batch systems, multiprogrammed systems, time-shared systems, personal computer systems, parallel systems, and distributed systems. It describes the simple structure of MS-DOS and the non-simple structure of UNIX. It also covers layered operating system approaches and microkernel system structures, comparing examples like Mach and the Darwin kernel in Mac OS X. The final topics to be covered in the next lecture are listed as operating system properties.

1. OPERATING SYSTEM
(R18 II(II Sem))
Department of computer science and engineering (AI & ML)
LEC 6
by
Asst.Prof.M.Gokilavani
VITS
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2. Syllabus
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3. 6/11/2023 Department of CSE (AI/ML) 3

4. TEXTBOOK:
• Operating System Principles- Abraham Silberchatz, Peter B. Galvin, Greg
Gagne 7th Edition, John Wiley.
• Advanced programming in the UNIX environment, W.R. Stevens, Pearson
education.
REFERENCES:
• Operating Systems – Internals and Design Principles Stallings, Fifth Edition–
2005, Pearson Education/PHI.
• Operating System A Design Approach- Crowley, TMH.
• Modern Operating Systems, Andrew S. Tanenbaum 2nd edition, Pearson/PHI.
• UNIX programming environment, Kernighan and Pike, PHI/ Pearson Education.
• UNIX Internals -The New Frontiers, U. Vahalia, Pearson Education
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5. Topics covered in Lec 6
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UNIT – I: Operating System - Introduction, Structures - Simple Batch,
Multiprogrammed, Time-shared, Personal Computer, Parallel, Distributed
Systems, Real-Time Systems, System components, Operating System
services, System Calls.

6. Operating System Structure
• General-purpose OS is very large program
• Various ways to structure ones
• Simple structure – MS-DOS
• More complex -- UNIX
• Layered – an abstraction
• Microkernel -Mach
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7. Simple Structure -- MS-DOS
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• MS-DOS – written to provide the most functionality in the least space
• Not divided into modules
• Although MS-DOS has some structure, its interfaces and levels of
functionality are not well separated.

8. Non Simple Structure -- UNIX
• UNIX – limited by hardware functionality, the original UNIX operating
system had limited structuring.
• The UNIX OS consists of two separable parts
• Systems programs
• The kernel
• Consists of everything below the system-call interface and above the
physical hardware
• Provides the file system, CPU scheduling, memory management, and
other operating-system functions; a large number of functions for one
level.
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9. Traditional UNIX System Structure
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10. Layered Approach
• The operating system is divided into a number of layers (levels), each built on top
of lower layers.
• The bottom layer (layer 0), is the hardware; the highest (layer N) is the user
interface.
• With modularity, layers are selected such that each uses functions (operations) and
services of only lower-level layers.
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11. Microkernel System Structure
• Moves as much from the kernel into user space
• Mach example of microkernel
• Mac OS X kernel (Darwin) partly based on Mach
• Communication takes place between user modules using message passing
Benefits:
• Easier to extend a microkernel
• Easier to port the operating system to new architectures
• More reliable (less code is running in kernel mode)
• More secure
Demerits:
• Performance overhead of user space to kernel space communication
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12. Microkernel System Structure
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Application
Program
File
System
Device
Driver
Interprocess
Communication
memory
managment
CPU
scheduling
messages
messages
microkernel
hardware
user
mode
kernel
mode

13. Topics to be covered in next Lec 7
•Operating System Properties
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Thank you!!!