CS403: Operating System : Lec 6 OS Structure.pptx

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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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!!!