What is an Operating System. Types of Operating Systems.

An operating system (OS) is Software consisting of group of Programs and data, that runs on computer Systems for the execution of various Application Software.

Types of Operating Systems

Real-time Operating System: It is a multitasking operating system that aims at executing real-time applications. Real-time operating systems often use specialized scheduling algorithms so that they can achieve a deterministic nature of behavior. The main object of real-time operating systems is their quick and predictable response to events. They either have an event-driven or a time-sharing design. An event-driven system switches between tasks based on their priorities while time-sharing operating systems switch tasks based on clock interrupts.

Multi-user and Single-user Operating Systems: The operating systems of this type allow a multiple users to access a computer system concurrently. Time-sharing system can be classified as multi-user systems as they enable a multiple user access to a computer through the sharing of time. Single-user operating systems, as opposed to a multi-user operating system, are usable by a single user at a time. Being able to have multiple accounts on a Windows operating system does not make it a multi-user system. Rather, only the network administrator is the real user. But for a Unix-like operating system, it is possible for two users to login at a time and this capability of the OS makes it a multi-user operating system.

Multi-tasking and Single-tasking Operating Systems: When a single program is allowed to run at a time, the system is grouped under a single-tasking system, while in case the operating system allows the execution of multiple tasks at one time, it is classified as a multi-tasking operating system. Multi-tasking can be of two types namely, pre-emptive or co-operative. In pre-emptive multitasking, the operating system slices the CPU time and dedicates one slot to each of the programs. Unix-like operating systems such as Solaris and Linux support pre-emptive multitasking. Cooperative multitasking is achieved by relying on each process to give time to the other processes in a defined manner. MS Windows prior to Windows 95 used to support cooperative multitasking.

Distributed Operating System: An operating system that manages a group of independent computers and makes them appear to be a single computer is known as a distributed operating system. The development of networked computers that could be linked and communicate with each other, gave rise to distributed computing. Distributed computations are carried out on more than one machine. When computers in a group work in cooperation, they make a distributed system.

Embedded System: The operating systems designed for being used in embedded computer systems are known as embedded operating systems. They are designed to operate on small machines like PDAs with less autonomy. They are able to operate with a limited number of resources. They are very compact and extremely efficient by design. Windows CE and Minix 3 are some examples of embedded operating systems.

How SMS works.?

How SMS Works

SMS, or Short Message Service, is the technology behind what we often refer to as ‘text messages’ or ‘SMSes’, as well as what allows for news alerts on cellular phones. In recent years SMS has ballooned to over a 50 billion dollar industry and is quickly taking the communications world by storm.

Short Message Service actually refers to a framework that uniquely allows computers, or in this case phones, to communicate with each other without the need of a central hub. With SMS, phones can find each other, send short packets of information back and forth, and do it all without any central computer to guide them. But because the system does not rely upon fixed lines like a land based telephone system does, the amount of information that can be sent at one time is limited in size. This depends on the language spoken, but for English letters this typically means around 150 characters (Chinese and Japanese letters are limited to 70).

Quite recently, however, new developments in the technology have allowed for even longer messages to be sent. Long or Concatenated SMS is a development that allows multiple messages to be combined to form a single message. In effect, what happens is that your phone actually sends out a few smaller messages and then the receiving phone simply compiles those messages so that for users on both ends, it appears as though the message were cohesive. While there are some limitations, the brilliance behind SMS is that because there is no need for central hubs, and thus the system can be expanded indefinitely without any concerns of it slowing down or becoming more expensive.

The most common form of SMS is ‘texting’. This usually takes place with a cellular phone in which individuals use the letters behind the number pad on their phone to spell out words and phrases and then send them out. Because many companies charge by the word, individuals have come up with a sort of ‘texting slang’ to cut down on the amount of words required to convey a particular message. For example, ‘gr8’ and ‘BTW’ mean ‘great’ and ‘by the way’. In addition, other words have just been shortened, such as ‘lata’ to mean ‘later’. Most users simply pick up the lingo through frequent use, and although some slang is widely understood and used, other shortcuts are developed within circles of friends and family.

The major advantage of SMS is its price. The price is typically $0.05 per message, a significant cut below that of traditional telephony and cell phone per-minute charges. The savings of SMS has its roots in the nature of the technology. Short Message Service, like SIP, is modeled on a peer to peer model and not a cog and wheel like traditional communication systems. This means that instead of having to route a message through a central hub, your text goes straight from you to its destination. This has radically cut down on the cost of SMS implementation and led to its overwhelming popularity throughout the world.

Short Message Service (SMS) has radically changed the face of the communications industry. While the practice has become quite common throughout the world, it has only recently become popular here in the United Stats, a growth partly predicated upon, surprisingly enough, its featured role in the show American Idol. The fact that ‘texting’ is quickly gaining both in popularity and recognition in the United States is not surprising however, due to its ability to offer users a cheap, quick, and often fun way to communicate with friends and family.

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Unix Shell Program on Nested if Statement.

Program:

echo "Example of the Nested If"

echo "Enter the Value of a"

read a

echo "Enter the value of b"

read b

if test $a -eq $b

then

echo a and b are equal

elif test $a -lt $b

then

echo a is lessthan b

else

echo a is greaterthan b

fi

Input/OutPut

Example of the Nested If

Enter the Value of a

7

Enter the value of b

9

a is lessthan b