Types of Operating Systems
Following are some of the most widely used types of Operating system.
If you don’t
know what Operating system is, you can learn from here.
1.
Simple Batch System
2.
Multiprogramming Batch System
3.
Multiprocessor System
4.
Desktop System
5.
Distributed Operating System
6.
Clustered System
7.
Real-time Operating System
8.
Handheld System
Simple Batch Systems
- In this
type of system, there is no direct interaction between user and
the computer.
- The
user has to submit a job (written on cards or tape) to a computer
operator.
- Then
computer operator places a batch of several jobs on an input device.
- Jobs
are batched together by type of languages and requirement.
- Then a
special program, the monitor, manages the execution of each program in the
batch.
- The
monitor is always in the main memory and available for execution.
Advantages of Simple Batch Systems
1.
No interaction between user and
computer.
2.
No mechanism to priorities the
processes.
Multiprogramming Batch Systems
- In this
the operating system picks up and begins to execute one of the jobs from
memory.
- Once
this job needs an I/O operation operating system switches to another job
(CPU and OS always busy).
- Jobs in
the memory are always less than the number of jobs on disk(Job Pool).
- If
several jobs are ready to run at the same time, then the system chooses
which one to run through the process of CPU Scheduling.
- In
Non-multiprogrammed system, there are moments when CPU sits idle and does
not do any work.
- In
Multiprogramming system, CPU will never be idle and keeps on processing.
Time
Sharing Systems are very similar to
Multiprogramming batch systems. In fact time sharing systems are an extension
of multiprogramming systems.
In Time
sharing systems the prime focus is on minimizing the response time,
while in multiprogramming the prime focus is to maximize the CPU usage.
Multiprocessor Systems
A
Multiprocessor system consists of several processors that share a common
physical memory. Multiprocessor system provides higher computing power and
speed. In multiprocessor system all processors operate under single operating
system. Multiplicity of the processors and how they do act together are
transparent to the others.
Advantages of Multiprocessor Systems
1.
Enhanced performance
2.
Execution of several tasks by
different processors concurrently, increases the system's throughput without
speeding up the execution of a single task.
3.
If possible, system divides task
into many subtasks and then these subtasks can be executed in parallel in
different processors. Thereby speeding up the execution of single tasks.
Desktop Systems
Earlier,
CPUs and PCs lacked the features needed to protect an operating system from
user programs. PC operating systems therefore were neither multiuser nor multitasking.
However, the goals of these operating systems have changed with time; instead
of maximizing CPU and peripheral utilization, the systems opt for maximizing
user convenience and responsiveness. These systems are called Desktop
Systems and include PCs running Microsoft Windows and the Apple Macintosh. Operating systems for these computers have benefited in
several ways from the development of operating systems for mainframes.
Microcomputers were immediately able to adopt some of the technology
developed for larger operating systems. On the other hand, the hardware costs
for microcomputers are sufficiently low that individuals have
sole use of the computer, and CPU utilization is no longer a prime concern.
Thus, some of the design decisions made in operating systems for mainframes may
not be appropriate for smaller systems.
Distributed Operating System
The
motivation behind developing distributed operating systems is the availability
of powerful and inexpensive microprocessors and advances in communication
technology.
These
advancements in technology have made it possible to design and develop
distributed systems comprising of many computers that are inter connected by
communication networks. The main benefit of distributed systems is its low
price/performance ratio.
Advantages Distributed Operating System
1. As there are multiple systems
involved, user at one site can utilize the resources of systems at other sites
for resource-intensive tasks.
2.
Fast processing.
3.
Less load on the Host Machine.
Types of Distributed Operating
Systems
Following
are the two types of distributed operating systems used:
1.
Client-Server Systems
2.
Peer-to-Peer Systems
Client-Server Systems
Centralized
systems today act as server
systems to satisfy requests generated by client systems.
The general structure of a client-server system is depicted in the figure
below:
Server
Systems can be broadly categorized as: Compute Servers and File
Servers.
- Compute
Server systems, provide an interface to which
clients can send requests to perform an action, in response to which they
execute the action and send back results to the client.
- File
Server systems, provide a file-system
interface where clients can create, update, read, and delete files.
Peer-to-Peer Systems
The growth
of computer networks - especially the Internet and World Wide Web (WWW) – has
had a profound influence on the recent development of operating systems. When
PCs were introduced in the 1970s, they were designed for personal use
and were generally considered standalone computers. With the beginning of
widespread public use of the Internet in the 1990s for electronic mail and FTP,
many PCs became connected to computer networks.
In contrast
to the Tightly Coupled systems, the computer networks used in
these applications consist of a collection of processors that do not share
memory or a clock. Instead, each processor has its own local memory. The
processors communicate with one another through various communication lines,
such as high-speed buses or telephone lines. These systems are usually referred
to as loosely coupled systems ( or distributed systems). The general structure
of a client-server system is depicted in the figure below:
Clustered Systems
- Like
parallel systems, clustered systems gather together multiple CPUs to
accomplish computational work.
- Clustered
systems differ from parallel systems, however, in that they are composed
of two or more individual systems coupled together.
- The
definition of the term clustered is not concrete; the
general accepted definition is that clustered computers share storage and
are closely linked via LAN networking.
- Clustering
is usually performed to provide high availability.
- A layer
of cluster software runs on the cluster nodes. Each node can monitor one
or more of the others. If the monitored machine fails, the monitoring
machine can take ownership of its storage, and restart the application(s)
that were running on the failed machine. The failed machine can remain
down, but the users and clients of the application would only see a brief
interruption of service.
- Asymmetric
Clustering - In this, one machine is
in hot standby mode while the other is running the applications. The hot
standby host (machine) does nothing but monitor the active server. If that
server fails, the hot standby host becomes the active server.
- Symmetric
Clustering - In this, two or more
hosts are running applications, and they are monitoring each other. This
mode is obviously more efficient, as it uses all of the available
hardware.
- Parallel
Clustering - Parallel clusters allow
multiple hosts to access the same data on the shared storage. Because most
operating systems lack support for this simultaneous data access by
multiple hosts, parallel clusters are usually accomplished by special
versions of software and special releases of applications.
Clustered
technology is rapidly changing. Clustered system's usage and it's features
should expand greatly as Storage Area Networks(SANs). SANs allow
easy attachment of multiple hosts to multiple storage units. Current clusters
are usually limited to two or four hosts due to the complexity of connecting
the hosts to shared storage.
Real Time Operating System
It is
defined as an operating system known to give maximum time for each of the
critical operations that it performs, like OS calls and interrupt handling.
The
Real-Time Operating system which guarantees the maximum time for critical
operations and complete them on time are referred to as Hard Real-Time
Operating Systems.
While the
real-time operating systems that can only guarantee a maximum of the time, i.e.
the critical task will get priority over other tasks, but no assurity of
completeing it in a defined time. These systems are referred to as Soft
Real-Time Operating Systems.
Handheld Systems
Handheld
systems include Personal Digital Assistants(PDAs), such as Palm-Pilots or Cellular Telephones with connectivity to a network such as the Internet.
They are usually of limited size due to which most handheld devices have a
small amount of memory, include slow processors, and feature small display
screens.
- Many
handheld devices have between 512 KB and 8 MB of
memory. As a result, the operating system and applications must manage
memory efficiently. This includes returning all allocated memory back to
the memory manager once the memory is no longer being used.
- Currently,
many handheld devices do not use virtual memory techniques,
thus forcing program developers to work within the confines of limited
physical memory.
- Processors
for most handheld devices often run at a fraction of the speed of a
processor in a PC. Faster processors require more power. To
include a faster processor in a handheld device would require a larger
battery that would have to be replaced more frequently.
- The
last issue confronting program designers for handheld devices is the small
display screens typically available. One approach for displaying the
content in web pages is web clipping, where only a small
subset of a web page is delivered and displayed on the handheld device.
Some handheld devices may use wireless technology such as BlueTooth, allowing remote access to e-mail and web browsing. Cellular telephones with connectivity to the Internet fall into this category. Their use continues to expand as network connections become more available and other options such as cameras and MP3 players, expand their utility.