Transcript Abstract View of System Components

Books Recommended:
1.Tanenbaum, A. S., “Operating Systems”, Prentice-Hall.2001
2.Nutt, G., “Operating Systems”, Addison-Wesley.2004
3.Penumuchu, C.V., “Simple Real-Time Operating System: A Kernel Inside
View”, Trafford Publishing. 2007
4.Singhal, M and Shivaratri, N.G., “Advanced Concepts in Operating
Systems”, McGraw-Hill.1994
5. George Colouris, Jean Dollimore, Tim Kinderberg, “Distributed Systems:
Concepts and Design”, 4th edition, Pearson. 2006
6. Pradeep K. Sinha, “Distributed Operating Systems: Concepts and Design”,
Pearson. 2009
7. William Stallings, “Distributed Operating Systems”
8. Dietel and Dietel, “Distributed Operating Systems”
9. Journal and Conference papers
10. Weblinks, Case Studies
Chapter 1: Introduction
•
•
•
•
•
•
•
•
What is an Operating System?
Mainframe Systems
Desktop Systems
Multiprocessor Systems
Distributed Systems
Clustered System
Real -Time Systems
Handheld Systems
Operating System Concepts
What is an Operating System?
• A program that acts as an intermediary
between a user of a computer and the
computer hardware.
• Operating system goals:
– Execute user programs and make solving user
problems easier.
– Make the computer system convenient to
use.
• Use the computer hardware in an
efficient manner.
Operating System Concepts
Operating System Revisited
USER
FILE
MANAGEMENT
DISK
MANAGEMENT
MEMORY
MANAGEMENT
KERNEL
File system and
directory
implementation,
access methods etc.
I/O , Disk
Scheduling etc.
Swapping,
Paging,
Segmentation,
Demand
Paging, Page
replacement,
Trashing etc.
Threads,
Processes, IPC,
Synchronization,
CPU Scheduling,
Deadlocks etc.
Computer System Components
1. Hardware – provides basic computing resources
(CPU, memory, I/O devices).
2. Operating system – controls and coordinates the
use of the hardware among the various
application programs for the various users.
3. Applications programs – define the ways in which
the system resources are used to solve the
computing problems of the users (compilers,
database systems, video games, business
programs).
4. Users (people, machines, other computers).
Operating System Concepts
Abstract View of System
Components
Operating System Concepts
Operating System Definitions
• Resource allocator – manages and
allocates resources.
• Control program – controls the
execution of user programs and
operations of I/O devices .
• Kernel – the one program running at all
times (all else being application
programs).
Operating System Concepts
Mainframe Systems
• Reduce setup time by batching similar
jobs
• Automatic job sequencing – automatically
transfers control from one job to another.
First rudimentary operating system.
• Resident monitor
– initial control in monitor
– control transfers to job
– when job completes control transfers pack to
monitor
Operating System Concepts
Memory Layout for a Simple Batch System
Operating System Concepts
Multiprogrammed Batch Systems
Several jobs are kept in main memory at the same time, and the
CPU is multiplexed among them.
Operating System Concepts
OS Features Needed for Multiprogramming
• I/O routine supplied by the system.
• Memory management – the system
must allocate the memory to several
jobs.
• CPU scheduling – the system must
choose among several jobs ready to
run.
• Allocation of devices.
Operating System Concepts
Time-Sharing Systems–Interactive Computing
• The CPU is multiplexed among several jobs that
are kept in memory and on disk (the CPU is
allocated to a job only if the job is in memory).
• A job swapped in and out of memory to the
disk.
• On-line communication between the user and
the system is provided; when the operating
system finishes the execution of one command,
it seeks the next “control statement” from the
user’s keyboard.
• On-line system must be available for users to
access data and code.
Operating System Concepts
Desktop Systems
• Personal computers – computer system
dedicated to a single user.
• I/O devices – keyboards, mice, display screens,
small printers.
• User convenience and responsiveness.
• Can adopt technology developed for larger
operating system’ often individuals have sole
use of computer and do not need advanced
CPU utilization of protection features.
• May run several different types of operating
systems (Windows, MacOS, UNIX, Linux)
Operating System Concepts
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
Operating System Concepts
Parallel Systems (Cont.)
• Symmetric multiprocessing (SMP)
– Each processor runs and identical copy of the
operating system.
– Many processes can run at once without
performance deterioration.
– Most modern operating systems support SMP
• Asymmetric multiprocessing
– Each processor is assigned a specific task; master
processor schedules and allocated work to slave
processors.
– More common in extremely large systems
Operating System Concepts
Symmetric Multiprocessing Architecture
Operating System Concepts
Distributed Systems
Operating System Concepts
Distributed Systems (cont)
• Requires networking infrastructure.
• Local area networks (LAN) or Wide
area networks (WAN)
• May be either client-server or peer-topeer systems.
Operating System Concepts
General Structure of Client-Server
Operating System Concepts
Clustered Systems
• Clustering allows two or more systems to
share storage.
• Provides high reliability.
• Asymmetric clustering: one server runs the
application while other servers standby.
• Symmetric clustering: all N hosts are running
the application.
Operating System Concepts
Real-Time Systems
• Often used as a control device in a
dedicated application such as
controlling scientific experiments,
medical imaging systems, industrial
control systems, and some display
systems.
• Well-defined fixed-time constraints.
• Real-Time systems may be either hard
or soft real-time.
Operating System Concepts
Real-Time Systems (Cont.)
• Hard real-time:
– Secondary storage limited or absent, data
stored in short term memory, or readonly memory (ROM)
– Conflicts with time-sharing systems, not
supported by general-purpose operating
systems.
• Soft real-time
– Limited utility
in industrial control of
Operating System Concepts
Handheld Systems
• Personal Digital Assistants (PDAs)
• Cellular telephones
• Issues:
– Limited memory
– Slow processors
– Small display screens.
Operating System Concepts
Similar Issues for
•Distributed OS
•Real Time OS
•Multimedia OS
•Security Aspects
•Case studies : Classical and Mobile OS
History of Commercial OS
Google OS for Handheld Devices : Android
Nokia OS for Handheld Devices : Symbian
Apple Mac OS for Handheld Devices : iPhone OS or iOS
Windows pocket PC :
Windows Mobile
2009 – 2010 : Microsoft Windows 7, Apple’s Mac “ Snow Leopard”, Google Chrome OS
2006 :
Microsoft Windows Vista
2002 - 2004 :
Red Hat, Solaris, Debian, Fedora Core, Suse, Ubuntu
1954 : MIT’s OS for UNIVAC 1103
1955 : GM OS for IBM 701
1964 : DOS for IBM Mainframes
1969 : AT&T designed Unix
1977 : Berkley Software Distribution, variant of Unix
1981 : IBM PC ( IBM + Microsoft ) and MS-DOS came up
1983 : Apple Lisa by Apple Inc.
1987 : Microsoft and IBM fall apart .
Microsoft : Graphical OS in 1993 : Windows NT, Windows 95, 98, Me etc. IBM : OS\2
1991 : Linux : Unix like OS Kernel
1996 : Macintosh system and its OS : Mac OS
1995 : Apple buys NeXT (released by Steve, ex-employee of Apple Inc.)
2001 : Apple abandons its OS and introduces Mac OS X ( Nod to X Window and X OS).
Windows responds by releasing Windows XP family
• Distributed Systems vs. Computer Networks
• Distributed System is collection of independent
computers that appears to its users as a single
coherent system.
• A software built on top of computer networks to
give it high degree of coherence and transparency
• There is a layer on top of operating system called
MIDDLEWARE for providing coherence.
• Eg. In WWW everything looks like a web document
Definition of a Distributed System (1)
A distributed system is:
A collection of independent computers that
appears to its users as a single coherent
system.
2 aspects of the definition:
•Hardware: machines are autonomous
•Software: users think of system as a single computer
Definition of a Distributed System (2)
Characteristics :
•The difference between various computers and way in which they
interact is hidden from users.
•Easy to expand and scale.
•Continuously available (w.r.t. faults)
•MIDDLEWARE to support heterogenous systems.
1.1
A distributed system organized as middleware.
Note that the middleware layer extends over multiple machines.
Examples of Distributed Systems:
• Network of workstations in university :If whole
system looks like single processor time sharing
system (multi – user).
• Workflow information system that supports
automatic processing of order
• WWW : URL based gigantic centralized document
system
Advantages of distributed systems
over centralized systems
• Economics: microprocessors offer a better
price/performance than mainframes
• Speed: distributed system may have more total
computing power than mainframe.
• Inherent distribution: some applications involve
spatially separated machines
• Reliability: if one machine crashes, the system as a
whole can still survive
• Incremental growth: Computing power can be
added in small increments
Disadvantages of distributed systems
• Software: little software exists for such systems
today
• Networking: the network can saturate or cause
other problems
• Security: easy access also applies to secret data
Goals
• Connecting users to resources : Eg. web documents,
printers, Groupware etc.
• Transparency : DS should be able to present its users that it
is a single computer system.
• Openness : System that offers services according to
standard rules that describe syntax and semantics of those
services.
In DS services specified through interfaces written in
Interface Definition Language (IDL) (analogous to protocols
in networks)
A process needs a certain interface to talk to another
process that provides that interface.
Scalability
Transparency in a Distributed System
Transparency
Description
Access
Hide differences in data representation and how a resource is
accessed. Eg. big endian vs little endian, various file naming
conventions etc.
Location
Hide where a resource is located. Achieved by assigning
logical names in url like www.hotmail.com/home.html
Migration
Hide that a resource may move to another location
Relocation
Hide that a resource may be moved to another location while
in use
Replication
Eg Mobile users with wireless laptops.
Concurrency
Hide that a resource may be shared by several competitive
users. Eg. Cooperative sharing (networks) vs. competitive
sharing (two users having same file server)
Failure
Hide the failure and recovery of a resource. For eg. “ Web
page unavailable” : Busy web server or server really down ?
Persistence
Hide whether a (software) resource is in memory or on disk
Different forms of transparency in a distributed system.
Scalability Problems
Concept
Example
Centralized services
A single server for all users
Centralized data
A single on-line telephone book
Centralized algorithms
Doing routing based on complete information
Examples of scalability limitations.
Distributed Algorithm :
1. No m/c has complete information about system state
2. Machines make decisions based on local information
3. Failure of a m/c do not ruin algorithm
4. There is no implicit assumption that clock exists
Scaling Techniques (1)
Asynchronous comm., replication (hiding comm latencies), distribution,
caching
1.4
The difference between letting:
a)
a server or
b)
a client check forms as they are being filled
Scaling Techniques (2)
1.5
An example of dividing the DNS name space into zones.
Flexibility
System should provide services in a flexible manner, preferably
by using a microkernel, as shown below (Amoeba o/s)
User
File
Directory
Process
Server
server
server
______________ __________________________
Microkernel | microk | microk |
microkernel
------------------------------------------------------------------Network
Microkernel
• The microkernel has a small footprint and only provides basic or
minimal services like, ipc, some memory management, low-level
scheduling (dispatching) and low level I/O .
• All other services should be implemented as user level services.
• This makes the system highly modular, with well-defined interfaces to
each of the services, so that each service is available to every client,
independent of location.
• It also makes it easy to implement, install and debug new services,
i.e., without stopping the system or booting a new kernel.
• Other alternative: Use a monolithic kernel, as in Sprite, where kernel
provides all service, this is faster, but less flexible.
Reliability
• issues of availability, consistency, security and fault-tolerance
• Availability is the fraction of time the system is usable. This can be
enhanced by designing such that it does not require the simultaneous
functioning of a substantial number of critical components.
Redundancy of key components also increases availability.
• Consistency implies that if file redundancy is there, thus all copies of
the file on different servers must have the same data. This is difficult
if updates are frequent.
• Security must be provided in the form of protection from
unauthenticated users and unauthorized usage – more difficult in
distributed systems.
• Fault-tolerance is to be provided so that when failures occur, they will
be transparent to users. A degraded service should still be available if
some servers go down.
Performance
• Efficient and speedy performance is a major
requirement, but difficult to achieve.
• Issues of response time, throughput, system
utilization and amount of network capacity
consumed are important.
• Speedup is never N times that of a centralized
system, because of the overhead of
communication, which is slow due to message
passing.