Advanced Operating Systems: Lecture 1 - Mr. Farhan Zaidi

Advanced Operating 
Systems
Introduction and Overview


Instructor’s introduction
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MS (Computer Science) University of Southern California, USA
BS Electrical Engineering, University of Engineering and Technology Lahore,
Pakistan
Over 15 years of professional experience in US and Pakistan industry as system
software architect, designer and developer in the field of embedded systems,
operating systems and computer networks.
Worked as senior software architect and team lead in Nortel Networks California
USA, Philips Semiconductors California USA, Zhone Technologies California
USA, Enabling Technologies Islamabad and CresSoft Inc. Islamabad Pakistan.
Designed and implemented embedded software for network routers, including
protocol stacks in real-time operating system kernels, switches, DSL access
multiplexers, TCP/IP core protocol and routing engines, multimedia software for
video conferencing and video encoding/decoding.
Currently working as the CTO of MediaRoutes Inc, where I am developing a SIP
(Session Initiation Protocol) based highly scalable state-full server for call proxy,

routing and registrations. The system is built on an asynchronous, event-driven
framework I have designed that can scale the SIP server to handle more than
100,000 concurrent SIP sessions. The framework will soon be available as
open-source under GNU public license.


Overview of today’s lecture
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Course Objectives and Pre-requisites
Introduction to what an operating system is?
Issues involved in the design of an operating system
Different types of operating systems
Re-cap of the lecture


Course objectives
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In depth treatment of topics from design
perspective.
Consider why things are done in a certain way
instead of just how they are done.
Consider design alternatives.
Be able to tell the difference between a good design
and a bad design.
Also consider engineering tradeoffs involved in the
design process.


Course Objectives (cont’d)
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Practical aspects from a computer scientist’s
perspective.
These include:
1. A case study throughout the course of a real
commercial operating system kernel. We will
present Linux kernel for this purpose. We will also
make comparisons to other operating systems e.g.
Windows where applicable.
2. Hands on training as a programmer on using
operating system services in relatively complex
programs. I will assign 4 to 5 programming
assignments for this purpose.


Course Objectives (cont’d)
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Research perspective
We will also look at some contemporary and
classical research on operating system topics in the
research literature. For this purpose, I will assign a
few readings from the literature on operating
systems.


Course Pre­requisites
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C/C++ programming. This is an essential prerequisite since without this, you won’t be able to do
the assignments.
An undergraduate first course on data structures.
This should include implementation of elementary
data structures e.g. lists, stack, queues, trees etc. in
a high level language like C or C++ etc.
A first course on operating systems would be helpful
but not strictly required since we will cover the
basics of each topic before diving into the deeper
stuff.


What is an operating system?
Top-down view

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Provides an extended or virtual machine abstraction to user
programs

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Easier to program than the underlying hardware.
All services are invoked and accomplished through system calls.

Bottom-up view
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Acts as a resource manager of a complex system
Resources consist of processors, memories, timers, disks,
mice, keyboard, network interfaces, printers etc.
OS manages allocation of these resources to user programs in
an orderly and controlled manner


Resource multiplexing
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OS multiplexes resources in two ways:
In time, In space
Time multiplexing involves different programs taking turns in
using the resource. Example: CPU scheduling, printer sharing.

Space multiplexing involves different program getting part of the
resource possibly at the same time. Example: memory is divided
into several running programs.


The major OS issues
Structure: how is the OS organized?
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Sharing: how are resources shared across users?
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Naming: how are resources named (by users or programs)?
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Security: how is the integrity of the OS and its resources
ensured?
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Protection: how is one user/program protected from another?
Performance: how do we make it all go fast?
Reliability: what happens if something goes wrong
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(either with hardware or with program)?
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Extensibility: can we add new features?
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Communication: how do programs exchange information,
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including across a network?
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More OS issues

Concurrency: how are parallel activates (computation and I/O
created and controlled?
Scale: what happens as demands or resources increase?
Persistence: how do you make data last longer than program executions?
Distribution: how do multiple computers interact with each other?
Accounting: how do we keep track of resources usage, and perhaps charge for it?


Protection and security as an example
None
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OS from my program
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Your program from my program
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My program from my program
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Access by intruding individuals
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Access by intruding programs
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Denial of service
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Distributed denial of service
Spoofing
Spam
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Worms
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Viruses

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Stuff you download and run knowingly (bugs, Trojan horses)
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Stuff you download and run unknowingly (cookies, spyware)
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Type of Operating Systems
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Main frame operating systems
Huge amounts of I/O activity. 1000s of disks not unusual
Provide batch, transaction and time sharing services.
Batch processing is routine non-interactive jobs. e.g. claims
processing, sales reporting etc.
Transaction processing systems handle large number of small
requests e.g. check processing in banks, air line reservations
etc.
Time-sharing systems allow multiple remote users to run jobs
at the same time e.g. querying a database.
OS Optimized for these tasks. Example is OS/390

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Server operating systems
Run on very large PCs, workstations or even main-frames.
They serve multiple users over a network simultaneously and
allow them to share hardware and software. Examples are web
servers, database transaction servers etc. Examples of OS in
this class are Win2K, XP and flavors of UNIX.

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Multiprocessor operating systems
OS is basically a variation to server operating systems
with special provisions for connectivity and
communication management between different CPUs.

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PC operating systems
OS provides a nice interface to a single user. Typically
used for word processing, spread sheets, Internet
access etc.


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Real-time operating systems
Characterized by time as the key parameter. Real-time response
to internal and external events is more important than any other
design goal. Classified into two sub-categories: Hard and Soft
real-time
Example applications include Industrial process control, robotics and
assembly lines, air traffic control, network routers and
telecommunication switches, multi-media systems etc.

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Embedded operating systems
Embedded in small devices e.g. palm-top computers e.g. PDA,
TV sets, micro-wave ovens, mobile phones. They have
characteristics of real-time systems (mainly soft real-time) but
also have restraints on power consumption, memory usage etc.
Examples include PalmOS and Windows CE. Height of this type
is smart-card systems.


Distributed Systems
Distribute the computation among several physical
processors.

Loosely coupled system – each processor has its
own local memory; processors communicate with one
another through various communications lines, such as
high-speed buses or telephone lines.

Advantages of distributed systems
Resources

Sharing
Computation speed up – load sharing
Reliability
Communications


Parallel Systems
Multiprocessor systems with more than on CPU in
close communication.

Tightly coupled system – processors share
memory and a clock; communication usually takes
place through the shared memory.

Advantages of parallel system:
Increased throughput
Economical
Increased

reliability
graceful degradation
fail-soft systems