Atomic
In ancient philosophy, an atom was the ultimate unit of matter on which more complex views of material reality were based. In computer programming, atomic describes a unitary action or object that is essentially indivisible, unchangeable, whole, and irreducible. Here are some usages:
1) In Structured Query Language, an atomic function is one that will either complete or return to its original state if a power interruption or an abnormal end occurs.
2) In some UNIX-base operating systems, an atomic operation is one in which no change can take place in the time between the setting of a mask and the receiving of a signal to change the mask.
3) In some programming languages, including Lisp, an atom is the basic unit of executable code or data.
atomic force microscopy
Atomic force microscopy (AFM) is a technique for analyzing the surface of a rigid material all the way down to the level of the atom. AFM uses a mechanical probe to magnify surface features up to 100,000,000 times, and it produces 3-D images of the surface.
The technique is derived from a related technology, called scanning tunneling microscopy (STM). The difference is that AFM does not require the sample to conduct electricity, whereas STM does. AFM also works in regular room temperatures, while STM requires special temperature and other conditions.
AFM is being used to understand materials problems in many areas, including data storage, telecommunications, biomedicine, chemistry, and aerospace. In data storage, it is helping researchers to "force" a disk to have a higher capacity. Today’s magnetic storage devices typically have a capacity limit of between 20 and 50 gigabits (billions of bits) per square inch of storage medium. Researchers are looking into AFM to help raise read and write densities to between 40 gigabits and 300 gigabits per square inch. No one has yet commercialized AFM technology for this purpose, but IBM and others are actively pursuing it.
attempt
In a telecommunications system, an attempt is a user request to get connected to the system or to initiate a call, whether or not the connection is made or the call is initiated.
attenuation
Attenuation is a general term that refers to any reduction in the strength of a signal. Attenuation occurs with any type of signal, whether digital or analog. Sometimes called loss, attenuation is a natural consequence of signal transmission over long distances. The extent of attenuation is usually expressed in units called decibels.
If Ps is the signal power at the transmitting end (source) of a communications circuit and Pd is the signal power at the receiving end (destination), then Ps > Pd. The power attenuation Ap in decibels is given by the formula:
Ap = 10 log10(Ps/Pd)
Attenuation can also be expressed in terms of voltage. If Av is the voltage attenuation in decibels, Vs is the source signal voltage, and Vd is the destination signal voltage, then:
Av = 20 logM(Vs/Vd)
In conventional and fiberoptic cables, attenuation is specified in terms of the number of decibels per foot, 1,000 feet, kilometer, or mile. The less the attenuation per unit distance, the more efficient the cable. When it is necessary to transmit signals over long distances via cable, one or more repeaters can be inserted along the length of the cable. The repeaters boost the signal strength to overcome attenuation. This greatly increases the maximum attainable range of communication.
attosecond
(This definition follows U.S. usage in which a billion is a thousand million and a trillion is a 1 followed by 12 zeros.)
An attosecond is one quintillionth (10-18) of a second and is a term used in photon research.
For comparison, a millisecond (ms or msec) is one thousandth of a second and is commonly used in measuring the time to read to or write from a hard disk or a CD-ROM player or to measure packet travel time on the Internet. A microsecond (|s or Greek letter mu plus s) is one millionth (10-6) of a second.
A nanosecond (ns or nsec) is one billionth (10-9) of a second and is a common measurement of read or write access time to random access memory (RAM).
A picosecond is one trillionth (10-12) of a second, or one millionth of a microsecond.
A femtosecond is one millionth of a nanosecond or 10-15 of a second and is a measurement sometimes used in laser technology.
attribute
In general, an attribute is a property or characteristic. Color, for example, is an attribute of your hair. In using or programming computers, an attribute is a changeable property or characteristic of some component of a program that can be set to different values.
In the Hypertext Markup Language (HTML), an attribute is a characteristic of a page element, such as a font. An HTML user can set font attributes, such as size and color, to different values. In some programming languages, such as PowerBuilder PowerScript, an attribute is a property of an object or may be considered a container for the property of the object. For example, color might be an attribute of a text object, containing the value of ”red.”
In a database management system (DBMS), an attribute may describe a component of the database, such as a table or a field, or may be used itself as another term for a field.
In the DOS operating system, file properties, such as ”readonly” or ”visible,” are called file attributes.
ATU-R
An ATU-R (ADSL Terminal Unit—Remote), sometimes called an ”ADSL modem,” is a hardware unit that is installed in any computer that uses a telephone company connection with Asymmetric Digital Subscriber Line (ADSL) service. The ATU-R connects to an Ethernet network interface card (NIC) in the computer and, on the other side, to a telephone jack in the home or business. Ideally (for less interference), the telephone jack hooks up to a new wire that goes to a signal splitter that the telephone company installs at the telephone company demarcation point (the place where the outside phone company wire or wires connect to the network of phone lines within the customer’s building). The splitter divides the signal into low frequencies for voice and high frequencies for data.
ATV
ATV (Advanced Television) is the name given by the U.S. Federal Communications Commission to digital TV (DTV), the use of digital transmission of video and audio information on broadcast channels and cable TV. ATV includes both high-definition television (HDTV), a format for digital video compression, transmission, and presentation and also the creation of additional channels on the current analog 6 MHz channel. For additional information, see HDTV.
ATX
ATX is an industry-wide open specification for a desktop computer’s motherboard. The most current version (December, 1996) is Specification 2.0.
ATX improves the motherboard design by taking the small AT motherboard that has been an industry standard and rotating by 90 degrees the layout of the microprocessor and expansion slots. This allows space for more full-length add-in cards. A double-height aperture is specified for the rear of the chassis, allowing more possible I/O arrangements for a variety of devices such as TV input and output, LAN connection, and so forth. The new layout is also intended to be less costly to manufacture. Fewer cables will be needed. The power supply has a side-mounted fan, allowing direct cooling of the processor and cards, making a secondary fan unnecessary. Version 2.0 incorporates improvements suggested by chassis and power supply vendors.
Almost all major computer manufacturers, including IBM, Compaq, and Apple build desktops with ATX motherboards. IBM is using ATX in both Intel and PowerPC platforms.
audible ring
In a telephone system, an audible ring is the tone that is returned from the called party’s switching device and heard by the caller. This tone indicates to the caller that the desired party is being rung.
audio
Audio is sound within the acoustic range available to humans. An audio frequency (AF) is an electrical alternating current within the 20 to 20,000 hertz (cycles per second) range that can be used to produce acoustic sound. In computers, audio is the sound system that comes with or can be added to a computer. An audio card contains a special built-in processor and memory for processing audio files and sending them to speakers in the computer. An audio file is a record of captured sound that can be played back. Sound is a sequence of natural analog signals that are converted to digital signals by the audio card, using a microchip called an analog-to-digital converter (ADC). When sound is played, the digital signals are sent to the speakers where they are converted back to analog signals that generate varied sound.
Audio files are usually compressed for storage or faster transmission. Audio files can be sent in short stand-alone segments—for example, as files in the Wave file format. In order for users to receive sound in real-time for a multimedia effect, listening to music, or in order to take part in an audio or video conference, sound must be delivered as streaming sound. More advanced audio cards support wavetable, or precaptured tables of sound. The most popular audio file format today is MP3 (MPEG-1 Audio Layer-3).
Audio Engineers Society/European Broadcasting Union
AES/EBU (Audio Engineering Society/European Broadcasting Union) is the name of a digital audio transfer standard. The AES and EBU developed the specifications for the standard.
The AES/EBU digital interface is usually implemented using 3-pin XLR connectors, the same type connector used in a professional microphone. One cable carries both left-and right-channel audio data to the receiving device. AES/ EBU is an alternative to the S/PDIF standard.
In audio, noise is generally any unpleasant sound and, more technically, any unwanted sound that is unintentionally added to a desired sound. Ambient sound itself is a series of changes in air pressure transmitted in waves from the sound source to anyone with the sensory apparatus to detect the waves (human beings and other animals with ears, for example). Sound waves are expressed as a series of analog sine waves. The combination and blend of these waves gives sounds their individual characteristics, making them pleasant or unpleasant to listen to. Some sounds are combination of waves that are related to each other, as in the case of a pitched instrument that transmits one dominant frequency of sound wave and additional frequencies that enhance the fundamental or dominant frequency. An oboe is an example of a pitched instrument. Other sounds are made from a grouping of tightly spaced waves that do not have a specific fundamental frequency that is dominant over the others. A snare drum is an example.
In recording sound, noise is often present on analog tape or low-fidelity digital recordings. The standard audio cassette includes a layer of hiss on every recording. When doing digital recording, the conversion of a sound file from 16-bit to 8-bit adds a layer of noise.
White noise is a sound that contains every frequency within the range of human hearing (generally from 20 hertz to 20 kHz) in equal amounts. Most people perceive this sound as having more high-frequency content than low, but this is not the case. This perception occurs because each successive octave has twice as many frequencies as the one preceding it.
For example, from 100 Hz to 200 Hz, there are one hundred discrete frequencies. In the next octave (from 200 Hz to 400 Hz), there are two hundred frequencies.
White noise can be generated on a sound synthesizer. Sound designers can use this sound, with some processing and filtering, to create a multitude of effects such as wind, surf, space whooshes, and rumbles.
Pink noise is a variant of white noise. Pink noise is white noise that has been filtered to reduce the volume at each octave. This is done to compensate for the increase in the number of frequencies per octave. Each octave is reduced by 6 decibels, resulting in a noise sound wave that has equal energy at every octave.
audit trail
In accounting, an audit trail is the sequence of paperwork that validates or invalidates accounting entries. In computing, the term is also used for an electronic or paper log used to track computer activity. For example, a corporate employee might have access to a section of a network in a corporation such as billing but be unauthorized to access all other sections. If that employee attempts to access an unauthorized section by typing in passwords, this improper activity is recorded in the audit trail.
Audit trails are used to record customer activity in e-commerce. The customer’s initial contact is recorded in an audit trail as well as each subsequent action such as payment and delivery of the product or service. The customer’s audit trail is then used to respond properly to any inquiries or complaints. A company might also use an audit trail to provide a basis for account reconciliation, to provide a historical report to plan and support budgets, and to provide a record of sales in case of a tax audit. Audit trails are also used to investigate cybercrimes. In order for investigators to expose a hacker’s identity, they can follow the trail the hacker left in cyberspace. Sometimes hackers unknowingly provide audit trails through their Internet service providers’ activity logs or through chat room logs.
auditor
In Web advertising, this usually means a third-party company that audits the number of visitors to or impression sent from a Web site during some time period. When you try to sell advertising, having a third-party auditor gives the prospect more confidence in your audience numbers.
AUI
The AUI (attachment unit interface) is the 15-pin physical connector interface between a computer’s network interface card (NIC) and an Ethernet cable. On 10Base-5 ("thicknet") Ethernet, a short cable is used to connect the AUI on the computer with a transceiver on the main cable. In 10Base-2 or "thinnet" Ethernet networks, the NIC connects directly to the Ethernet coaxial cable at the back of the computer. IEEE 802.3, the Ethernet standard, defines the AUI 15-pin physical layer interface. This interface is also called a DB-15 interface or a DIX interface (DIX refers to the three major companies who helped standardize Ethernet: Digital Equipment Corporation, Intel, and Xerox).
authentication
Authentication is the process of determining whether someone or something is, in fact, who or what it is declared to be. In private and public computer networks (including the Internet), authentication is commonly done through the use of logon passwords. Knowledge of the password is assumed to guarantee that the user is authentic. Each user registers initially (or is registered by someone else), using an assigned or self-declared password. On each subsequent use, the user must know and use the previously declared password. The weakness in this system for transactions that are significant (such as the exchange of money) is that passwords can often be stolen, accidentally revealed, or forgotten.
For this reason, Internet business and many other transactions require a more stringent authentication process. The use of digital certificates issued and verified by a Certificate Authority (CA) as part of a public key infrastructure is considered likely to become the standard way to perform authentication on the Internet.
Logically, authentication precedes authorization (although they may often seem to be combined).
authentication, authorization, and accounting
Authentication, authorization, and accounting (AAA) is a term for a framework for intelligently controlling access to computer resources, enforcing policies, auditing usage, and providing the information necessary to bill for services. These combined processes are considered important for effective network management and security.
Authentication provides a way of identifying a user, typically by having the user enter a valid user name and valid password before access is granted. The process of authentication is based on each user having a unique set of criteria for gaining access. The AAA server compares a user’s authentication credentials with other user credentials stored in a database. If the credentials match, the user is granted access to the network. If the credentials are at variance, authentication fails and network access is denied.
Following authentication, a user must gain authorization for doing certain tasks. After logging into a system, for instance, the user may try to issue commands. The authorization process determines whether the user has the authority to issue such commands. Simply put, authorization is the process of enforcing policies: determining what types or qualities of activities, resources, or services a user is permitted. Usually, authorization occurs within the context of authentication. Once you have authenticated a user, they may be authorized for different types of access or activity. The final plank in the AAA framework is accounting, which measures the resources a user consumes during access. This can include the amount of system time or the amount of data a user has sent and/or received during a session. Accounting is carried out by logging of session statistics and usage information and is used for authorization control, billing, trend analysis, resource utilization, and capacity planning activities.
Authentication, authorization, and accounting services are often provided by a dedicated AAA server, a program that performs these functions. A current standard by which network access servers interface with the AAA server is the Remote Authentication Dial-In User Service (RADIUS).
authorization
Authorization is the process of giving someone permission to do or have something. In multi-user computer systems, a system administrator defines for the system which users are allowed access to the system and what privileges of use (such as access to which file directories, hours of access, amount of allocated storage space, and so forth). Assuming that someone has logged in to a computer operating system or application, the system or application may want to identify what resources the user can be given during this session. Thus, authorization is sometimes seen as both the preliminary setting up of permissions by a system adminstrator and the actual checking of the permission values that have been set up when a user is getting access. Logically, authorization is preceded by authentication.
authorized program analysis report
An APAR (authorized program analysis report) is a term used in IBM for a description of a problem with an IBM program that is formally tracked until a solution is provided. An APAR is created or "opened" after a customer (or sometimes IBM itself) discovers a problem that IBM determines is due to a bug in its code. The APAR is given a unique number for tracking and a target date for solution. When the support group that maintains the code solves the problem, it develops a program temporary fix (PTF) that, when applied, possibly with a SuperZap, will temporarily solve the problem for the customers that may be affected. The PTF will "close" the APAR. PTFs can be applied individually but are usually made available as part of a fix package that includes a number of PTFs. Meanwhile, the PTFs are provided to the development group that is working on the next product release. The developers may or may not use the PTFs (since these are temporary fixes), but will determine and design the correct problem solution to incorporate in the next product release.
Autoexec.bat
AUTOEXEC.BAT is a file containing Disk Operating System commands that are executable when the computer is booted (started). The commands in AUTOEXEC.BAT tell the operating system which application programs are to be automatically started, how memory is to be managed, and initialize other settings. Each command in AUTOEXEC.BAT could be typed in manually after the computer is started, but that would take too long. The AUTOEXEC.BAT file is, in fact, a command script that is written beforehand so that it can be automatically executed when the operating system is started. The BAT suffix stands for batch, indicating that this is a file containing a sequence of commands entered from a file rather than interactively by a user.
