In computer technology and telecommunications, online indicates a state of connectivity, and offline indicates a disconnected state. In modern terminology, this usually refers to an Internet connection. More broadly, it could also refer to any piece of equipment or functional unit that is connected to a larger system. Being online means that the equipment or subsystem is connected, or that it is ready for use. "Online" has come to describe activities and concepts that take place on the Internet, such as online identity, online predator and online shop. A similar meaning is also given by the prefixes cyber and e, as in words cyberspace, cybercrime, email, and e-commerce. In contrast, "offline" can refer to either computing activities performed while disconnected from the Internet, or alternatives to Internet activities (such as shopping in brick-and-mortar stores). The term "offline" is sometimes used interchangeably with the acronym "IRL", meaning "in real life", as well as about office meetings in person wherein a formal, high-concentration meeting may have matters taken "offline" to a more relaxed moment away from the "online" high-stress meeting.
History During the 19th century, the term on line was commonly used in both the railroad and telegraph industries. For railroads, a signal box would send messages down the line (track), via a telegraph line (cable), indicating the track's status: Train on line or Line clear. Telegraph linemen would refer to sending current through a line as direct on line or battery on line; or they may refer to a problem with the circuit as being on line, as opposed to the power source or end-point equipment. Since at least 1950, in computing, the terms on-line and off-line have been used to refer to whether machines, including computers and peripheral devices, are connected or not. Here is an excerpt from the 1950 book High-Speed Computing Devices:
The use of automatic computing equipment for large-scale reduction of data will be strikingly successful only if means are provided for the automatic transcription of these data to a form suitable for automatic entry into the machine. For some applications, of which the most prominent are those in which the reduced data are used to control the process being measured, the input must be developed for on-line operation. In on-line operation the input is communicated directly and without delay to the data-reduction device. For other applications, off-line operation, involving automatic transcription of data in a form suitable for later introduction to the machine, may be tolerated. These requirements may be compared with teleprinter operating requirements. For example, some teletype machines operate on line. Their operators are in instantaneous communication. Other teletype machines are operated off line, through the intervention of punched paper tape. The message is preserved by means of holes punched in the tape and is transmitted later by feeding the tape to another machine.
Examples
Offline e-mail One example of a common use of these concepts with email is a mail user agent (MUA) that can be instructed to be in either online or offline states. One such MUA is Microsoft Outlook. When online it will attempt to connect to mail servers (to check for new mail at regular intervals, for example), and when offline it will not attempt to make any such connection. The online or offline state of the MUA does not necessarily reflect the connection status between the computer on which it is running and the Internet i.e. the computer itself may be online—connected to the Internet via a cable modem or other means—while Outlook is kept offline by the user, so that it makes no attempt to send or to receive messages. Similarly, a computer may be configured to employ a dial-up connection on demand (as when an application such as Outlook attempts to make a connection to a server), but the user may not wish for Outlook to trigger that call whenever it is configured to check for mail.
Offline media playing Another example of the use of these concepts is digital audio technology. A tape recorder, digital audio editor, or other device that is online is one whose clock is under the control of the clock of a synchronization master device. When the sync master commences playback, the online device automatically synchronizes itself to the master and commences playing from the same point in the recording. A device that is offline uses no external clock reference and relies upon its own internal clock. When many devices are connected to a sync master it is often convenient, if one wants to hear just the output of one single device, to take it offline because, if the device is played back online, all synchronized devices have to locate the playback point and wait for each other device to be in synchronization. (For related discussion, see MIDI timecode, Word clock, and recording system synchronization.)
Offline browsing
… excerpt ends here. Continue reading the full article.
