"Online" redirects here. For the Brad Paisley song of the same name, see Online (song). For the magazine, see ONLINE. For the feature film, see On Line. For the Nevada power line, see ONLine.
The terms "online" and "offline" (also stylized as "on-line" and "off-line") have specific meanings in regard to computer technology and telecommunications. In general, "online" indicates a state of connectivity, while "offline" indicates a disconnected state. In common usage, "online" often refers to the Internet or the World Wide Web.
The concepts have however been extended from their computing and telecommunication meanings into the area of human interaction and conversation, such that even offline can be used in contrast to the common usage of online (e.g., "I bought those Marcus Fenix figurines offline").
In computer technology and telecommunication, online and offline are defined by Federal Standard 1037C. They are states or conditions of a "device or equipment" or of a "functional unit". To be considered online, one of the following must apply to a device:
Under the direct control of another device
Under the direct control of the system with which it is associated
Available for immediate use on demand by the system without human intervention
Connected to a system, and is in operation
Functional and ready for service
In contrast, a device that is offline meets none of these criteria (e.g., its main power source is disconnected or turned off, or it is off-power).
One example of a common use of these concepts is a mail user agent 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. That is, the computer itself may be online—connected to 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 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 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 a large number of 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 sync, and recording system synchronization.)
A third example of a common use of these concepts is a web browser that can be instructed to be in either online or offline states. The browser only attempts to fetch pages from servers whilst in the online state. In the offline state, users can perform offline browsing, where pages can be browsed using local copies of those pages that have previously been downloaded whilst in the on-line state. This can be useful when the computer is offline and connection to the Internet is impossible or undesirable. The pages are either downloaded implicitly into the web browser's own cache as a result of prior online browsing by the user, or explicitly by a browser configured to keep local copies of certain web pages, which are updated when the browser is in the online state, either by checking that the local copies are up-to-date at regular intervals or by checking that the local copies are up-to-date whenever the browser is switched to the on-line state. One such web browser capable of being explicitly configured to download pages for offline browsing is Internet Explorer. When pages are added to the Favourites list, they can be marked to be "available for offline browsing". Internet Explorer will download to local copies both the marked page and, optionally, all of the pages that it links to. In Internet Explorer version 6, the level of direct and indirect links, the maximum amount of local disc space allowed to be consumed, and the schedule on which local copies are checked to see whether they are up-to-date, are configurable for each individual Favourites entry.
Offline browsing known as "Offline favourites" was removed as a feature in Internet Explorer 7, which now only supports saving single web pages, but not an entire site.
Similarly, offline storage is computer data storage that is not "available for immediate use on demand by the system without human intervention."
Online and offline distinctions have been generalized from computing and telecommunication into the field of human interpersonal relationships. The distinction between what is considered online and what is considered offline has become a subject of study in the field of sociology.
The distinction between online and offline is conventionally seen as the distinction between computer-mediated communication and face-to-face communication (e.g. face time), respectively. Online is virtuality or cyberspace, and offline is reality (i.e., Real life or meatspace). Slater states that this distinction is "obviously far too simple". To support his argument that the distinctions in relationships are more complex than a simple online/offline dichotomy, he observes that some people draw no distinction between an on-line relationship, such as indulging in cybersex, and an offline relationship, such as being pen pals. He also argues that even the telephone can be regarded as an online experience in some circumstances, and that the blurring of the distinctions between the uses of various technologies (such as PDA and mobile phone, television and Internet, and telephone and Voice over Internet Protocol) has made it "impossible to use the term on-line meaningfully in the sense that was employed by the first generation of Internet research".
Slater asserts that there are legal and regulatory pressures to reduce the distinction between online and offline, with a "general tendency to assimilate online to offline and erase the distinction," stressing, however, that this does not mean that online relationships are being reduced to pre-existing offline relationships. He conjectures that greater legal status may be assigned to online relationships (pointing out that contractual relationships, such as business transactions, online are already seen as just as "real" as their offline counterparts), although he states it to be hard to imagine courts awarding palimony to people who have had a purely online sexual relationship. He also conjectures that an online/offline distinction may be seen by people as "rather quaint and not quite comprehensible" within 10 years.
This distinction between online and offline is sometimes inverted, with online concepts being used to define and to explain offline activities, rather than (as per the conventions of the desktop metaphor with its desktops, trash cans, folders, and so forth) the other way around. Several cartoons appearing in The New Yorker have satirized this. One includes Saint Peter asking for a username and a password before admitting a man into Heaven. Another illustrates "the off-line store" where "All items are actual size!" shoppers may "Take it home as soon as you pay for it!" and "Merchandise may be handled prior to purchase!"