Essential Properties of OS

Batch - group of jobs submitted to machine together. A job was originally presented to the machine (and its human operator) in the form of a set of cards - these cards held information according to how ``punched'' out of the cardboard. The operator grouped all of the jobs into various batches with similar characteristics before running them (all the quick jobs might run, then the slower ones, etc.).

• Operator collects job, orders efficiently, runs one at a time
• Amortize setup costs over many jobs
• Keep machine busy while programmer thinks
• User must wait for results until batch collected and submitted

Result: Improved system throughput and utilization, but lost interactivity.

Time-sharing - is sharing a computing resource among many users by multitasking. Its introduction in the 1960s, and emergence as the prominent model of computing in the 1970s, represents a major historical shift in the history of computing. By allowing a large number of users to interact simultaneously on a single computer, time-sharing dramatically lowered the cost of providing computing, while at the same time making the computing experience much more interactive.

It refers to the concurrent use of a computer by more than one user -- users share the computer's time. Time sharing is synonymous withmulti-user. Almost all mainframes and minicomputers are time-sharingsystems, but most personal computers and workstations are not.

Real time - occurring immediately. The term is used to describe a number of different computer features. For example, real-time operating systemsare systems that respond to input immediately. They are used for such tasks as navigation, in which the computer must react to a steady flow of new information without interruption. Most general-purpose operating systems are not real-time because they can take a few seconds, or even minutes, to react.

Real time can also refer to events simulated by a computer at the same speed that they would occur in real life. In graphics animation, for example, a real-time program would display objects moving across thescreen at the same speed that they would actually move.

Network - is a group of two or more computer systems linked together. There are many types of computer networks, including:

local-area networks (LANs) : The computers are geographically close together (that is, in the same building).

wide-area networks (WANs) : The computers are farther apart and are connected by telephone lines or radio waves.

campus-area networks (CANs): The computers are within a limited geographic area, such as a campus or military base.

metropolitan-area networks MANs): A data network designed for a town or city.

home-area networks (HANs): A network contained within a user's home that connects a person's digital devices.

In addition to these types, the following characteristics are also used to categorize different types of networks:

topology : The geometric arrangement of a computer system. Common topologies include a bus, star, and ring. See theNetwork topology diagrams in the Quick Reference section of Webopedia.

protocol : The protocol defines a common set of rules and signals that computers on the network use to communicate. One of the most popular protocols for LANs is called Ethernet. Another popular LAN protocol for PCs is the IBM token-ring network .

architecture : Networks can be broadly classified as using either a peer-to-peer or client/server architecture.

Computers on a network are sometimes called nodes. Computers anddevices that allocate resources for a network are called servers.

Distributed - refers to any of a variety of computer systems that use more than onecomputer, or processor, to run an application. This includes parallel processing, in which a single computer uses more than one CPU toexecute programs. More often, however, distributed processing refers tolocal-area networks (LANs) designed so that a single program can run simultaneously at various sites. Most distributed processing systemscontain sophisticated software that detects idle CPUs on the networkand parcels out programs to utilize them.

Another form of distributed processing involves distributed databases,databases in which the data is stored across two or more computer systems. The database system keeps track of where the data is so that the distributed nature of the database is not apparent to users.

Handheld - is a portable computer that is small enough to be held in one's hand. Although extremely convenient to carry, handheld computers have not replaced notebook computers because of their small keyboards and screens. The most popular hand-held computers are those that are specifically designed to provide PIM (personal information manager)functions, such as a calendar and address book.

Some manufacturers are trying to solve the small keyboard problem by replacing the keyboard with an electronic pen. However, these pen-based devices rely on handwriting recognition technologies, which are still in their infancy.