Modern Operating Systems
B.Ramamurthy
Chapter 2, Section 2.4
Topics
 New developments and influences
 Microkernel Architecture
 Multithreading
 Symmetric Multiprocessing
 Distributed Systems
 Object-oriented design
 Windows NT architecture
 Traditional Unix Kernel
 Summary
New Developments
Hardware : increased machine speed,
high speed network attachments,
increased size of memory storage, lower
cost
Application : multimedia, internet,
intranet, Web computing, client/server
computing
Software : Object Oriented design and
programming
Influences on OS
Wide range of design approaches:
1. Microkernel architecture
2. Multithreading
3. Symmetric multiprocessing
4. Distributed Operating Systems
5. Object-oriented design
Microkernel Architecture
 Essential services such as address space management,
interprocess communications, and basic scheduling are
done by the kernel.
 For the rest of the services special servers are designed
separately.
 Flexibility in design and for support of distributed
system.
 Highly suited for customizing services for various
environments.
 Example: Mach system, CTRX realtime kernel for 8051
Multithreading
A thread is dispatchable unit of work.
Many threads can execute the code in the same
process space.
Code for multithread should be re-entrant :
What is reentracy?
Also known as lightweight process since the
overhead in thread switching and control is
much less compared to process control
switching.
Example: Windows NT , Solaris
Symmetric
Multiprocessing (SMP)
Many of today’s systems have multiple
microprocessors
The architecture is known as SMP if the
processors share the same main memory and
IO space and can be used interchangeably. (do
the same functions)
For performance and reliability (availability,
maintainability, scalability, fault-tolerance).
Ex: Windows NT and Solaris
Distributed Systems
A distributed system is a collection of
independent computers that appear to the users
of the system as a single computer.
In this age of geographically distributed data
sources and clients this model works very well.
Question is : network connected, networktransparent, network-centric model, or clusters?
Object Oriented Design
Lends discipline to the process of extending
small kernels.
Customization of the operating system
without disrupting system integrity.
Forms the basis for remote location of
services, mobility, accountability, security
etc.
Supports Client-server paradigm of computing.
Example: Windows NT
Features of Windows NT (
Fig.2.13)
User mode and Kernel mode : Separation
of user and kernel functions.
Modified microkernel architecture.
Windows NT Executive: Executive services
HAL : Hardware Abstraction Layer :
abstract unberlying machine (alpha, intel,
etc.)
System services (user interface)
Features of Traditional
Unix kernel
User level kernel level
System call subsystem
User programs may access kernel thru’
libraries or directly thru’ system calls:
Which one preferred and why?
File Subsystem, Process Control
subsystem
Study Fig 2.17 (modern unix kernel
functions)
Summary
Major OS Topics include: Process
management, File management,
scheduling, IO management, concurrency,
memory management, security.
Keep up with recent developments.
Distribution of services and resources is
an very critical topic.