Transcript Types of services

Distributed System Concepts and
Architectures
Services
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Overview
 Service provider?
 Who are involved in providing the services?
 Types of services
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
Basic services
Fundamental services
 References
Service provider?
Operating system is the service
provider. An operating system is a
program that acts as an intermediary
between the user of a computer and the
computer hardware.
Continued…
The purpose of an operating system is
to provide an environment in which a
user can execute programs in a
convenient and efficient manner.
Thus we can say that:
An OS is
Continued….
 Tool to make programmer's job easy
 Resource allocator


Must be fair; not partial to any process,
specially for process in the same class
Must discriminate between different class of
jobs with different service requirements
 Control program
 Layered architecture
Layer structure of a computer
system
Overview
 Service provider?
 Who are involved in providing the services?
 Types of services


Basic services
Fundamental services
 References
Who are involved in providing the
services?
Since I am describing all the things
here taking Unix as standard operating
system. I would like to discuss here
Shell and Kernel.
Shell
 Unix command interpreter

Interprets the first word of a command line
as a command name
 Is a user program and not part of the
kernel
 Redirection of input and output
 Background jobs
Kernel
 Permanently resides in the main memory
 Controls the execution of processes by
allowing their creation, termination or
suspension, and communication
 Schedules processes fairly for execution on
the CPU
 Allocates main memory for an executing
process
Continued…
 File system maintenance
 Allows processes controlled access to
peripheral devices such as terminals,
tape drives, disk drives, and network
devices.
Overview
 Service provider?
 Who are involved in providing the services?
 Types of services


Basic services
Fundamental services
 References
Basic Services
 Program execution
 I/O operations
 File-system manipulation
 Communications
 Error detection
Program execution
The system must be able to load a
program into memory and to run that
program. The program must be able to
end its execution, either normally or
abnormally (indicating error).
I/O operations
A running program may require I/O.
This I/0 may involve a file or an I/O
device. For specific devices, special
functions may be desired (such as to
rewind a tape drive, or to blank a CRT
screen). For efficiency and protection,
users usually cannot control I/0 devices
directly.
Continued…
Therefore, the operating system must
provide a means to do I/O.
File-system manipulation
The file system is of particular interest.
Obviously, programs need to read and
write files. Programs also need to
create and delete files by name.
Communications
In many circumstances, one process
needs to exchange information with
another process. Such communication
can occur in two major ways. The first
takes place between processes that are
executing on the same computer;
Continued…
the second takes place between
processes that are executing on
different computer systems that are tied
together by a computer network.
Communications may be implemented
via shared memory,
Continued…
or by the technique of message passing,
in which packets of information are
moved between processes by the
operating system.
Error detection
The operating system constantly needs
to be aware of possible errors. Errors
may occur in the CPU and memory
hardware, in I/O devices and in the
user program. For each type of error,
the operating system should take the
appropriate action to ensure correct and
consistent computing.
Overview
 Service provider?
 Who are involved in providing the services?
 Types of services


Basic services
Fundamental services
 References
Fundamental services
 Primitive services
 Services by the system servers
 Value added services
Primitive services
Primitive services are those that must
be implemented on kernel of each node
in the system. In Distributed system
when communication is done through
message passing, a set of primitives for
send and receive must be defined and
implemented. Send and receive can be
Continued….
either synchronous or asynchronous.
Synchronous communication, in
addition to serving communication
purposes, carries the side benefit of
achieving internodes inter process
synchronization.
Services by the system servers
The services which can be
implemented anywhere in the system
and performs the functions which is
basic to the operation of a distributed
system. To achieve transparency in
Distributed System server mappes
physical objects with logical system
names.
Continued….
 Name server
Used to locate users, processes and machines.
 Directory Server
It is used in conjunction with files and
communication ports.
 Network server
Name server translation, selection of paths,
actual routing of information is done by network
server.
Value added services
Services that are not needed in the
implementation of a Distributed
System But useful in supporting
Distributed Application.
It is Used To increase the
computational performance and
enhancement of fault tolerance or by
need for cooperative activities.
Continued….
 Group Server
It manages the creation and termination of
group activities. It is also responsible for
Group addressing, communication, contain
information about membership, member
privileges and admission policies.
Web server is also the good example of a
value added server.
References
 Distributed operating systems & Algorithms, By
Randy chow, Theodore Johnson. 1998
 Operating System Concepts 6th ed - Silberschatz
Galvin, ch -3 operating System structure. 2003
 Advanced UNIX- A Programmer’s Guide, By
Stephen Prata. 1997
 Computer science illuminated, second edition, By
Nell dale, John Lewis. 2004
 http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnum
ber=138323
Thankyou