Amaya
Amaya is the Web browser that was developed by members of the World Wide Web Consortium (W3C) as a practical tool as well as a testing ground for W3C ideas. Amaya includes an HTML editor as well as a viewer and can be downloaded freely from the W3C Web site for use in either Linux or Windows 95/NT/2000 operating system. Amaya is distributed as open source software, meaning that software developers are free to add to or modify its code and extend its capabilities.
According to Web inventor and W3C Director Tim Berners-Lee, Amaya was developed because at the time no commercially available browser included editing capabilities. The idea was to develop the browser as a way to see why such capabilities hadn’t been provided and perhaps help solve any problems that were in the way. Amaya also offers a testing platform for other W3C developments such as MathML, a user interface for creating complex mathematical expressions. Berners-Lee and staff members use Amaya as their primary browser. Here are some interesting features of Amaya:
• A what-you-see-is-what-you-get (WYSIWYG) authoring interface similar to that of commercial products such as Microsoft’s FrontPage and the ability to upload the pages to a server
• Support for the latest level of HTML, XHTML
• The ability to work on either the coded HTML view or the WYSIWYG source view of the page
• Special support for people with disabilities
• Assurance that the Web page you create will be properly constructed so that other tools will know what to expect when they work with your page
• Assistance in creating and viewing hypertext links
• The ability to display images in the Portable Network Graphics format, a more capable graphic format than the Graphics Interchange Format format that is also free from licensing requirements
• The ability to print the table of contents or the table of links in a document
• An application program interface (API) in C for adding new functions or modifying existing ones. Amaya is also used within the W3C to experiment with the Java API used in the Document Object Model (DOM)
Amaya is the client counterpart to the W3C’s experimental Web server, Jigsaw (but you don’t need Jigsaw to use Amaya).
AMD
AMD is the second largest maker of personal computer microprocessors after Intel. They also make flash memory, integrated circuits for networking devices, and program mable logic devices. AMD reports that it has sold over 100 million x86 (Windows-compatible) microprocessors. Its Athlon (formerly called the "K7") microprocessor, delivered in mid-1999, was the the first to support a 200 MHz bus. In March 2000, AMD announced the first 1 gigahertz PC microprocessor in a new version of the Athlon.
Founded in 1969, AMD along with Cyrix has often offered computer manufacturers a lower-cost alternative to the microprocessors from Intel. AMD develops and manufactures its processors and other products in facilities in Sunnyvale, California, and Austin, Texas. A new fabrication facility was opened in Dresden, Germany, in 1999.
The lower cost of AMD’s microprocessors was a contributor to lower PC prices in the 1998-2000 period. Reviewers generally rated the K6 and Athlon equivalent to or slightly better than comparable Pentium microprocessors from Intel. In addition to ”the first mainstream 200 MHz system bus,” Athlon includes a superscalar pipelining floating point unit, and a programmable L1 and L2. The Athlon uses AMD’s aluminum 0.18 micron technology.
Amdahl’s law
In computer programming, Amdahl’s law is that, in a program with parallel processing, a relatively few instructions that have to be performed in sequence will have a limiting factor on program speedup such that adding more processors may not make the program run faster. This is generally an argument against parallel processing for certain applications and, in general, against overstated claims for parallel computing. Others argue that the kinds of applications for which parallel processing is best suited tend to be larger problems in which scaling up the number of processors does indeed bring a corresponding improvement in throughput and performance.
American Registry of Internet Numbers
The American Registry of Internet Numbers (ARIN) is the organization in the U.S. that manages IP address numbers for the U.S. and assigned territories. Because Internet addresses must be unique and because address space on the Internet is limited, there is a need for some organization to control and allocate address number blocks. IP number management was formerly a responsibility of the Internet Assigned Numbers Authority (IANA), which contracted with Network Solutions Inc. for the actual services. In December 1997, IANA turned this responsibility over to
ARIN, which, along with Reseaux IP Europeens (RIPE) and Asia Pacific Network Information Center (APNIC), now manages the world’s Internet address assignment and allocation. Domain name management is still the separate responsibility of Network Solutions and a number of other registrars accredited by the Internet Corporation for Assigned Names and Numbers (ICANN).
For Internet Protocol Version 6 (IPv6), which extends the length of an Internet address from 32 bits to 128 bits, ARIN will have many more addresses to manage and allocate.
American Wire Gauge
American Wire Gauge (AWG) is a U.S. standard set of non-ferrous wire conductor sizes. The ”gauge” means the diameter. Non-ferrous includes copper and also aluminum and other materials, but is most frequently applied to copper household electrical wiring and telephone wiring. Typical household wiring is AWG number 12 or 14. Telephone wire is usually 22, 24, or 26. The higher the gauge number, the smaller the diameter and the thinner the wire. Since thicker wire carries more current because it has less electrical resistance over a given length, thicker wire is better for longer distances. For this reason, where extended distance is critical, a company installing a network might prefer telephone wire with the lower-gauge, thicker wire of AWG 24 to AWG 26.
AWG is sometimes known as Brown and Sharpe (B&S) Wire Gauge.
Amiga
Amiga is a personal computer designed especially for high-resolution, fast response graphics and multimedia applications. Its microprocessor is based on Motorola’s 680×0 line of processors. It was one of the first computers to offer true color. It comes with its own operating system, AmigaOS. Since its first appearance from Commodore Business Machines in 1985, Amiga has become a synonym for fast, high-resolution graphics and best known for its quickly responsive user interface and suitability for playing action games. AmigaOS handles 32-bit instructions and uses preemptive multitasking. Its design favors user input to the extent that it is sometimes described as a realtime operating system (RTOS).
Since Amiga was designed as a special-purpose system, AmigaOS, which is written in C and assembler language, is especially compact. All versions of the operating system will run on 512 kilobytes of RAM. All versions of the Amiga can run at 50 MHz or faster, using an accelerator card. A G4 processor can be used through adding an accelerator card. The Amiga supports plug and play and can be adapted with software to emulate Windows and Mac OS.
The Amiga has the ability to become a video monitor by locking into a video signal from an external source such as a video camera. As a result, Amigas are used by television stations and sports arenas to display video clips on large screens.
Amiga is working on a ”Next Generation" system that will use Linux as its basic core. (Earlier plans favored another operating system, QNX.)
ampere
An ampere is a unit of measure of the rate of electron flow or current in an electrical conductor. One ampere of current represents one coulomb of electrical charge (6.24 x 1018 charge carriers) moving past a specific point in one second. Physicists consider current to flow from relatively positive points to relatively negative points; this is called conventional current or Franklin current. The ampere is named after Andre Marie Ampere, French physicist (1775-1836).
ampere hour
An ampere hour (abbreviated Ah, or sometimes amp hour) is the amount of energy charge in a battery that will allow one ampere of current to flow for one hour. A milliampere hour (mAh) is 1,000th of an Ah, and is commonly used as a measure of charge in portable computer batteries. The mAh provides an indication of how long the PC will operate on its battery without having to recharge it.
ampere per meter
The ampere per meter (symbolized A/m) is the International Unit of magnetic field strength. It is derived from basic standard units, but is expressed directly in base units and cannot be further reduced.
Consider the interior of a long, cylindrical coil with a single winding and an air core. Suppose that the linear current density in this coil is 1 ampere per meter of displacement as measured along the coil axis. (This expression differs from current density per unit area, which is expressed in amperes per meter squared.) Then the magnetic field strength in the interior of the coil is defined as 1 A/m.
For a given coil, the magnetic field strength is directly proportional to the linear current density. Thus, if the linear current density doubles, so does the magnetic field strength; if the linear current density becomes 1/10 as great, the magnetic field strength also diminishes by a factor of 10. Sometimes, magnetic field strength is expressed in units called oersteds (symbolized Oe). The oersted is a larger unit than the ampere per meter. Approximate conversions are:
Also see ampere, current, magnetic field, meter, and International System of Units (SI).
ampere per meter squared
The ampere per meter squared, symbolized A/m2, is the International Unit of electric current density. A current density of 1 A/m2 represents one ampere of electric current flowing through a material with a cross-sectional area of one square meter.
The ampere per meter squared is a small unit of current density. Suppose a wire has a cross-sectional area of one millimeter squared (1 mm2). This is 0.000001 meter squared (10-6 m2). If the current density in this wire is 1 A/m2, then the wire carries 10-6 A, or one microampere (1 mA), a tiny current. Suppose this same wire carries a current of one ampere (1 A), which is an entirely plausible scenario. Then the current density in the wire is 1,000,000 amperes per meter squared (106 A/m2).
Sometimes, larger units of current density are specified. For example, one ampere per millimeter squared (A/mm2) represents a current of 1 A flowing through a conductor with a cross-sectional area of 1 mm. This unit is equal to 1,000,000 (106) A/m2. One milliampere per millimeter squared (mA/ mm2) represents a current of 1 mA flowing through a conductor with a cross-sectional area of 1 mm. This unit is equal to 1,000 (103) A/m2.
Determination of current density is straightforward in direct-current (DC) and low-frequency alternating-current (AC) circuits, because the current is distributed uniformly throughout the cross section of a solid conductor. But at radio frequencies (RF), more current flows near the outer surface of a solid conductor than near its center. This is known as skin effect, and it dramatically reduces the conductivity of wires in RF applications as compared with DC and low-frequency AC circuits. At RF, current density is sometimes near zero near the center of a solid conductor,and quite high near the outer periphery. The average current density can nevertheless be calculated according to the following formula: D = I/X where D is the current density in amperes per meter squared, I is the current in amperes, and X is the cross-sectional area of the conductor in meters squared.
Also see ampere, meter squared, skin effect, and International System of Units (SI).
Amplification factor
The amplification factor, also called gain, is the extent to which an analog amplifier boosts the strength of a signal. Amplification factors are usually expressed in terms of power.
The decibel (dB), a logarithmic unit, is the most common way of quantifying the gain of an amplifier. For power, doubling the signal strength (an output-to-input power ratio of 2:1) translates into a gain of 3 dB; a tenfold increase in power (output-to-input ratio of 10:1) equals a gain of 10 dB; a hundredfold increase in power (output-to-input ratio of 100:1) represents 20 dB gain. If the output power is less than the input power, the amplification factor in decibels is negative. If the output-to-input signal power ratio is 1:1, then the amplification factor is 0 dB.
Power amplifiers typically have gain figures from a few decibels up to about 20 dB. Sensitive amplifiers used in wireless communications equipment can show gain of up to about 30 dB. If higher gain is needed, amplifiers can be cascaded, that is, hooked up one after another. But there is a limit to the amplification that can be attained this way. When amplifiers are cascaded, the later circuits receive noise at their inputs along with the signals. This noise can cause distortion. Also, if the amplification factor is too high, the slightest feedback can trigger oscillation, rendering an amplifier system inoperative.
amplifier
An amplifier is an electronic device that increases the voltage, current, or power of a signal. Amplifiers are used in wireless communications and broadcasting, and in audio equipment of all kinds. They can be categorized as either weak-signal amplifiers or power amplifiers. Weak-signal amplifiers are used primarily in wireless receivers. They are also employed in acoustic pickups, audio tape players, and compact disc players. A weak-signal amplifier is designed to deal with exceedingly small input signals, in some cases measuring only a few nanovolts (units of 10-9 volt). Such amplifiers must generate minimal internal noise while increasing the signal voltage by a large factor. The most effective device for this application is the field-effect transistor. The specification that denotes the effectiveness of a weak-signal amplifier is sensitivity, defined as the number of microvolts (units of 10-6 volt) of signal input that produce a certain ratio of signal output to noise output (usually 10 to 1).
Power amplifiers are used in wireless transmitters, broadcast transmitters, and hi-fi audio equipment. The most frequently-used device for power amplification is the bipolar transistor. However, vacuum tubes, once considered obsolete, are becoming increasingly popular, especially among musicians. Many professional musicians believe that the vacuum tube (known as a "valve" in England) provides superior fidelity.
Two important considerations in power amplification are power output and efficiency. Power output is measured in watts or kilowatts. Efficiency is the ratio of signal power output to total power input (wattage demanded of the power supply or battery). This value is always less than 1. It is typically expressed as a percentage. In audio applications, power amplifiers are 30 to 50 percent efficient. In wireless communications and broadcasting transmitters, efficiency ranges from about 50 to 70 percent. In hi-fi audio power amplifiers, distortion is also an important factor. This is a measure of the extent to which the output waveform is a faithful replication of the input waveform. The lower the distortion, in general, the better the fidelity of the output sound.
Amplitude modulation
Amplitude modulation (AM) is a method of impressing data onto an alternating-current (AC) carrier waveform. The highest frequency of the modulating data is normally less than 10 percent of the carrier frequency. The instantanous amplitude (overall signal power) varies depending on the instantaneous amplitude of the modulating data.
In AM, the carrier itself does not fluctuate in amplitude. Instead, the modulating data appears in the form of signal components at frequencies slightly higher and lower than that of the carrier. These components are called sidebands. The lower sideband (LSB) appears at frequencies below the carrier frequency; the upper sideband (USB) appears at frequencies above the carrier frequency. The LSB and USB are essentially "mirror images" of each other in a graph of signal amplitude versus frequency, as shown in the illustration. The sideband power accounts for the variations in the overall amplitude of the signal.
When a carrier is amplitude-modulated with a pure sine wave, up to 1/3 (33 percent) of the overall signal power is contained in the sidebands. The other 2/3 of the signal power is contained in the carrier, which does not contribute to the transfer of data. With a complex modulating signal such as voice, video, or music, the sidebands generally contain 20 to 25 percent of the overall signal power; thus the carrier consumes 75 to 80 percent of the power. This makes AM an inefficient mode. If an attempt is made to increase the modulating data input amplitude beyond these limits, the signal will become distorted, and will occupy a much greater bandwidth than it should. This is called overmodulation, and can result in interference to signals on nearby frequencies.
