Optical fiber
Optical fiber (or ”fiber optic”) refers to the medium and the technology associated with the transmission of information as light pulses along a glass or plastic wire or fiber. Optical fiber carries much more information than conventional copper wire and is in general not subject to electromagnetic interference and the need to retransmit signals. Most telephone company long-distance lines are now of optical fiber.
Transmission on optical fiber wire requires repeaters at distance intervals. The glass fiber requires more protection within an outer cable than copper. For these reasons and because the installation of any new wiring is labor-intensive, few communities yet have optical fiber wires or cables from the phone company’s branch office to local customers (known as local loop).
Single mode fiber is used for longer distances; multimode fiber fiber is used for shorter distances.
optical media
Optical media—such as the compact disc (CD)—are storage media that hold content in digital form and that are written and read by a laser; these media include all the various CD and DVD variations, as well as optical jukeboxes and autochangers. Optical media have a number of advantages over magnetic media such as the floppy disk. Optical disc capacity ranges up to 6 gigabytes; that’s 6 billion bytes compared to the 1.44 megabytes (MB)—1,440,000 bytes—of the floppy. One optical disc holds about the equivalent of 500 floppies worth of data. Durability is another feature of optical media; they last up to seven times as long as traditional storage media.
The Optical Storage Technology Association (OSTA) is an international trade organization dedicated to the promotion of standardized writable optical technologies and related products. Incorporated in 1992, OSTA is made up of members and associates from the leading optical media manufacturers and resellers of North America, Europe, and Asia. OSTA members include Adaptec, Hewlett-Packard, Philips, and Sony.
optical mouse
An optical mouse is an advanced computer pointing device that uses a light-emitting diode (LED), an optical sensor, and digital signal processing (DSP) in place of the traditional mouse ball and electromechanical transducer. Movement is detected by sensing changes in reflected light, rather than by interpreting the motion of a rolling sphere.
The optical mouse takes microscopic snapshots of the working surface at a rate of more than 1,000 images per second. If the mouse is moved, the image changes. The tiniest irregularities in the surface can produce images good enough for the sensor and DSP to generate usable movement data. The best surfaces reflect but scatter light; an example is a blank sheet of white drawing paper. Some surfaces do not allow the sensor and DSP to function properly because the irregularities are too small to be detected. An example of a poor optical-mousing surface is unfrosted glass.
In practice, an optical mouse does not need cleaning, because it has no moving parts. This all-electronic feature also eliminates mechanical fatigue and failure. If the device is used with the proper surface, sensing is more precise than is possible with any pointing device using the old electromechanical design. This is an asset in graphics applications, and it makes computer operation easier in general.
opt-in e-mail
Opt-in e-mail is a Web marketing term for promotional email that recipients have previously requested by signing up at a Web site or special ad banner. Typically, Web users are invited to sign up for promotional information about one or more categories of products or services. Those who sign up have thus ”opted in.” Anyone sending them e-mail as a result hopes that the message will not be perceived as unwanted spam.
Several companies gather sign-ups at their own site or through specially-designed banner ads and then sell marketers mailing lists of those who have signed up in various interest categories. The marketer sending opt-in email may remind the recipient that they have previously indicated they were interested in receiving such e-mail and that this is not spam. The recipient is given an opportunity to be removed from the mailing list if they so choose. The distribution model of sending unsolicited e-mail (spam) and allowing the recipient to request removal is sometimes referred to as ”opt-out.”
Opt-in e-mail has been endorsed as the best practice for marketers by the Internet Direct Marketing Bureau (IDMB).
optoelectronics
Optoelectronics is a branch of electronics that overlaps with physics. The field concerns the theory, design, manufacture, and operation of hardware that converts electrical signals to visible or infrared radiation (infrared) energy, or vice-versa.
Examples of optoelectronic components include photocells, solar cells, optoisolators (also called optical couplers or optocouplers), LEDs (light-emitting diodes), and laser diodes. Applications include electric eyes, photovoltaic power supplies, various monitoring and control circuits, and optical fiber communications systems.
optoisolator
Also see diode.
An optoisolator, also known as an optical coupler or optocoupler, is a semiconductor device that allows signals to be transferred between circuits or systems, while keeping those circuits or systems electrically isolated from each other. Optoisolators are used in a wide variety of communications, control, and monitoring systems. In its simplest form, an optoisolator consists of an light-emitting diode (LED), IRED (infrared-emitting diode), or laser diode for signal transmission, and a photosensor for signal reception. The ”transmitter” takes the electrical signal and converts it into a a beam of modulated visible light or infrared (IR). This beam travels across a transparent gap and is picked up by the ”receiver,” which converts the modulated light or IR back into an electrical signal. The electrical output waveform is identical to the electrical input waveform, although the input and output amplitudes (signal strengths) often differ. The optoisolator is enclosed in a single package, and has the appearance of an integrated circuit (IC) or a transistor with extra leads.
A common application of an optoisolator is in a specialized modem that allows a computer to be connected to a telephone line without risk of damage from electrical transients (also called ”surges” or ”spikes”). Two optoisolators are employed in the analog section of the device: one for upstream signals and the other for downstream signals. If a transient occurs on the telephone line (and these are common), the computer will be unaffected because the optical gap does not conduct electric current. For this reason, modems that use optoisolators provide superior protection against transients compared with modems incorporating electrical surge suppressors alone. (An electrical surge suppressor should be installed between the optoisolator and the telephone line for optimum protection.)
Orange Book
Orange Book is the informal name for Philips and Sony’s Recordable CD Standard. Published in 1990, the Orange Book is a follow-up to their Red Book CD-DA (Compact Disc—Digital Audio) specifications. The Orange Book is divided into two sections: Part I deals with magneto-optical (MO) drives, and Part II deals with the first recordable CD format CD-R (Compact Disc—Recordable). Part III, released separately, describes CD-RW (Compact Disc—Rewritable). In addition to specifying these CD forms, the Orange Book includes information about data organization, multisession and hybrid discs, pre-groove modulation (for motor control during writing), and recommendations for measuring reflectivity, environment, and light speed.
Orange Book specifications enabled the first desktop disc writing. Formerly, CDs had been read-only music (CD-DA), to be played in CD players, and multimedia (CD-ROM), to be played in computers. After the Orange Book, any user with a CD Recorder drive could create their own CDs from their desktop computers.
Magneto-optical (CD-MO) technology allows tracks to be erased and rewritten on 12cm CDs that are rated to allow millions of rewrites. These drives use two heads (one to write and the other to erase), in a double-pass process. System information may be permanently written in a small, premastered area, but the rest of the area is available for recording, and re-recording many times.
CD-R products can be written to only once, similarly to WORM (write once, read many) products. A CD-R drive records on CDs that have special recording layers and pregrooved tracks. The first tracks are a program calibration area, which is followed by the lead-in area (where the table of contents will be written), and the program area (where the user actually records), and a lead-out area. There are hybrid discs that include read-only and recordable areas.
Rewritable CD (CD-RW) was developed by Philips and Sony in 1996, as an extension to the original Orange Book. This addition specifies the use of Phase Change technology and the Universal Disc Format (UDF) to produce a CD that can be rewritten in one pass. CD-RW makes it possible for the user to write and rewrite the disc.
ORBS
A similar but unrelated term is ORB (Object Request Broker).
ORBS (Open Relay Behavior-modification System) is (or possibly was—as of June 7, 2001, it was not operating) a volunteer-run New Zealand-based organization that operates an anti-spam screening service. The ORBS database tracks e-mail (specifically SMTP) servers that allow third-party relay (TPR), a practice that makes it possible for any sender to connect to the server from anywhere and forward volumes of unsolicited bulk e-mail messages. As a further precaution, ORBS also tracks networks that have set up processes to prevent verification of third-party relay permission, since administrators sometimes find it easier to block ORBS testers than to address security problems. In the first years of the Internet’s operation, third-party relaying was a necessary and accepted means of routing messages. Although technological advances have made third-party relaying no longer required, many servers continue to maintain open relays, according to ORBS, in the ”Internet’s spirit of cooperation.” According to ORBS, however, an open relay now falls into the category of ”attractive nuisance.” The organization claims that since 1995, the culture of the Web has changed dramatically, with the result that open relays became vulnerable to spammers looking to make a quick profit through bulk junk mail.
ORBS maintains a blacklist of Internet service providers (ISPs) and other organizations found in violation of their criteria, a practice that is somewhat controversial because the targeted enterprises often believe they have been listed unfairly. In one recent instance, a New Zealand high court ruled that ORBS must remove Xtra mail servers (owned by Actrix, an New Zealand-based ISP) from their list of suspect servers. ORBS is in occasionally acrimonious competition with a similar system based in California, the Mail Abuse Prevention System (MAPS). The two organizations clashed when ORBS blacklisted Above.net (an ISP owned by Paul Vixie, who also runs MAPS) as an open relay.
order of magnitude
An order of magnitude is an exponential change of plus-or-minus 1 in the value of a quantity or unit. The term is generally used in conjunction with power-of-10 scientific notation.
In base 10, the most common numeration scheme worldwide, an increase of one order of magnitude is the same as multiplying a quantity by 10. An increase of two orders of magnitude is the equivalent of multiplying by 100, or 102. In general, an increase of n orders of magnitude is the equivalent of multiplying a quantity by 10n. Thus, 2315 is one order of magnitude larger than 231.5, which in turn is is one order of magnitude larger than 23.15.
As values get smaller, a decrease of one order of magnitude is the same as multiplying a quantity by 0.1. A decrease of two orders of magnitude is the equivalent of multiplying by 0.01, or 10-2. In general, a decrease of n orders of magnitude is the equivalent of multiplying a quantity by 10-n. Thus, 23.15 is one order of magnitude smaller than 231.5, which in turn is one order of magnitude smaller than 2315.
In the International System of Units (SI), most quantities can be expressed in multiple or fractional terms according to the order of magnitude. For example, attaching the prefix ”kilo-” to a unit increases the size of the unit by three orders of magnitude, or one thousand (103). Attaching the prefix ”micro-” to a unit decreases the size of the unit by six orders of magnitude, the equivalent of multiplying it by one millionth (10-6). Scientists and engineers have designated prefix multipliers from septillionths (10-24) to septillions (1024), a span of 48 orders of magnitude.
ordinal
Ordinal refers to the sequence in which something is in relation to others of its kind. Examples of ordinal numbers are first, third, 11th, and 123rd. Ordinal numbers can be contrasted to cardinal numbers.
org
"org" is one of the generic top-level domain names that can be used when choosing a domain name. It generally describes the entity owning the domain name as one that does not fit into other categories. In general, non-profit organizations and industry standard groups tend to use this generic name. Along with the second-level domain name (for example: "moma" in moma.org), the top-level domain name is required in Web and e-mail addresses. For more information, see gTLD (generic top-level domain name).
original equipment manufacturer
An OEM (original equipment manufacturer) is a company that uses product components from one or more other companies to build a product that it sells under its own company name and brand. (The term is sometimes mistakenly used to refer to the company that supplies the components.) IBM is an example of a supplier to the OEM market (and IBM is also an OEM itself since it uses other companies’ parts in some of its products).
Many computer hardware manufacturers that have their own brand-name products derive considerable revenue by reselling the product or key parts of it to OEM companies that seem to be competing in the same market. Arguments for selling to an OEM are that you may be able to make money from a market sector that your competitor already owns (perhaps because they have an existing customer base) and that you can be a more efficient producer because you sell and manufacture more of your product. Frequently, an OEM company differentiates itself from the company it buys parts from by adding features or using different selling concepts. Many OEM companies are selling a "solution" tailored to a particular vertical market.
Also see value-added reseller (VAR), a somewhat similar repackaging of software.
orphan file
On a computer’s hard drive, an orphan file is a support file (such as a DLL file) that no longer serves a purpose because the "parent" application it is associated with has been moved or uninstalled. Orphan files can be deleted manually if the user is confident that the file is not being used by any other application.
orthogonal
In geometry, orthogonal means "involving right angles” (from Greek ortho, meaning right, and gon meaning angled). The term has been extended to general use, meaning the characteristic of being independent (relative to something else). It also can mean: non-redundant, non-overlapping, or irrelevant. In computer terminology, something—such as a programming language or a data object—is orthogonal if it can be used without consideration as to how its use will affect something else.
In itself, a programming language is orthogonal if its features can be used without thinking about how that usage will affect other features. Pascal is sometimes considered to be an orthogonal language, while C++ is considered to be a non-orthogonal language.
Features of a program that is compatible with its own earlier versions—this is called backward compatible—have an orthogonal relationship with the features of the earlier version, because they are mutually independent; you don’t have to worry about how the use of one version’s features will cause an unintended effect because of an interaction with those of the other version. Both the features and the programs can be said to be mutually orthogonal.
The length of time data is kept in storage in a computer system is known as its persistence. Orthogonal persistence is the quality of a programming system that allows a programmer to treat data similarly without regard to the length of time the data is kept in storage. Data is stored for varying lengths of time; some is stored very briefly and some is stored relatively permanently. Frequently, a programmer must use different approaches and separate coding to access data depending on whether it is stored for a long time or a short time. Using a programming system with orthogonal data persistence allows the programmer to treat data the same way regardless of its persistence characteristic, saving programming time and making it easier to enforce referential integrity (a type of constraint applied to ensure correct data validity).
orthogonal frequency-division multiplexing
Orthogonal frequency-division multiplexing (OFDM) is a method of digital modulation in which a signal is split into several narrowband channels at different frequencies. The technology was first conceived in the 1960s and 1970s during research into minimizing interference among channels near each other in frequency.
In some respects, OFDM is similar to conventional frequency-division multiplexing (FDM). The difference lies in the way in which the signals are modulated and demodulated. Priority is given to minimizing the interference, or crosstalk, among the channels and symbols comprising the data stream. Less importance is placed on perfecting individual channels.
OFDM is used in European digital audio broadcast services. The technology lends itself to digital television, and is being considered as a method of obtaining high-speed digital data transmission over conventional telephone lines. It is also used in wireless local area networks.
Also see frequency-division multiplexing (FDM), time-division multiplexing (TDM), and multi-carrier modulation (MCM).
OS X
OS X (pronounced OH-ESS-TEHN—the ”X” is Roman number X) is version 10 of the Apple Macintosh operating system (OS). OS X is described by Apple as its first ”complete revision” of the OS (the previous version is OS 9) and incorporates support for UNIX-based applications as well as for those written just for the Macintosh. The operating system is described as redesigned for modularity so that future changes will be easier to incorporate.
A very visible difference in OS X from earlier Mac OS versions is a desktop with a 3-D appearance. OS X also includes the ability to play Quicktime movies in icon size and instant wake-from-sleep capability on portable computers. Features that Apple says will be added include support for DVD movies and the ability to create audio CDs.
OS X can be installed on an existing Mac with OS 9 and the user can choose which one to use when the computer is started.
OS/2
OS/2 is an IBM operating system for the personal computer that was initially intended to provide an alternative to Microsoft Windows for both enterprise and personal PC users. The latest version of OS/2 Warp, Warp 4, has a Netscape-based Web browser that exploits OS/2′s existing speech recognition capability. IBM has also enhanced OS/2 to provide server functions for e-business.
OS/390
OS/390, recently renamed z/OS, is the IBM operating system most commonly installed on its S/390 line of mainframe server. It is an evolved version of MVS (Multiple Virtual Storage), IBM’s long-time, robust mainframe operating system. By whatever name, MVS has been said to be the operating system that keeps the world going. The payroll, accounts receivable, transaction processing, database management, and other programs critical to the world’s largest businesses are usually run on an MVS system. Although MVS tends to be associated with a monolithic, centrally-controlled information system, IBM has in recent years repositioned it as a ”large server” in a network-oriented distributed environment that would tend to use a 3-tier application model.
Since MVS represents a certain epoch and culture in the history of computing and since many older MVS systems still operate, the term ”MVS” will probably continue to be used for some time. Since OS/390 also comes with UNIX user and programming interfaces built in, it can be used as both an MVS system and a UNIX system at the same time. OS/390 (and earlier MVS) systems run older applications developed using COBOL and, for transaction programs, CICS. Older application programs written in PL/I and FORTRAN are still running. Older applications use the Virtual Storage Access Method for file management and Virtual Telecommunications Access Method for telecommunication with users. The most common program environment today uses the C and C++ languages. DB2 is IBM’s primary. Java applications can be developed and run under OS/390′s UNIX environment.
For additional information about major components of OS/ 390, see MVS. Other IBM operating systems for their larger computers include or have included: the Transaction Processing Facility (TPF), used in some major airline reservation systems, and virtual machine, an operating system designed to serve many interactive users at the same time.
