Acknowledgement Definition, What is Acknowledgement

In computing, an Acknowledgement is a signal passed between communicating processes or computers to signify acknowledgement, or receipt of response, as part of a communications protocol. For instance, Acknowledgement packets are used in the Transmission Control Protocol during establishment and termination of connections.

Short for acknowledgement, ACK is a response given by another computer or network device indicating to another computer that it acknowledged the SYN/ACK or other request sent to it.

Access Denied Definition, What is Access Denied

Access Denied is a message displayed when unable to obtain access to a location that you have not been granted the proper access rights or do not have permission to access.

If you are attempting to access a network share or resource on a network, Intranet, or the Internet and are receiving this error, you must contact the administrator or individual responsible for that network to obtain rights to that resource.

Although this error is commonly caused by a user accessing something he or she may not have rights to access, this error can also be caused by a hardware error. If you are attempting to access a hardware device on your computer (not a network) and are receiving this error, it is possible you may have a problem with that device. We recommend you review the support page in our hardware database for additional help or information with the hardware device.

Accelerator Definition, What is Accelerator

Accelerator is usually a device or program designed to improve the speed of a hardware peripheral or software program.

A good example of an accelerator would be a graphics or 3D accelerator. A graphics accelerator is a hardware peripheral that contains its own processor and RAM enabling the card to perform at accelerated speeds without decreasing the performance of the computer.

Other examples of accelerators are various utilities used to increase the performance of hardware devices. For example, a download accelerator is used to help increase the speed of download times on computer modems.

Hardware Accelerator

In computing, hardware acceleration is the use of hardware to perform some function faster than is possible in software running on the normal (general purpose) CPU. Examples of hardware acceleration include blitting acceleration functionality in graphics processing units (GPUs) and instructions for complex operations in CPUs.

The hardware that performs the acceleration, when in a separate unit from the CPU, is referred to as a hardware accelerator, or often more specifically as graphics accelerator or floating-point accelerator, etc. Those terms, however, are outdated and have been replaced with more descriptive terms like video card or graphics card.

Web Accelerator

A web accelerator is a proxy server that reduces web site access times. Web accelerators may use several techniques to achieve this reduction:

• They may cache recently or frequently accessed documents so they may be sent to the client with less latency or at a faster transfer rate than the remote server could.
• They may freshen objects in the cache ensuring that frequently accessed content is readily available for display.
• They may prefetch documents that are likely to be accessed in the near future.
• They may compress documents to a smaller size, for example by reducing the quality of images or by sending only what's changed since the document was last requested.
• They may filter out ads and other undesirable objects so they are not sent to the client at all.
• They may maintain persistent TCP connections between the client and the proxy server.

Web accelerators may be installed on the client (browsing) computer / mobile device or on ISP hosted servers or both. Accelerating delivery through compression requires some type of host based server to collect, compress and then deliver content to a client computer.

As of July 2006, these applications generally serve to improve dial-up, broadband and other connections that users may not be getting the best speed from. Many users can achieve a 2 to 10 times speed increase in average browsing experience, while some report a 5 to 20 times speed increases for specific web sites and pages. Many ISPs offer web accelerators as a part of their dial up and broadband services. Web accelerators are typically designed for web browsing and, sometimes, for e-mailing and can not improve speeds of streaming, gaming, P2P downloads or many other Internet applications.

Other web accelerators are targeted at the web site or web application owners. This type of web accelerator is installed in front of web servers and application servers and use a variety of the above techniques to improve performance to all users accessing the accelerated web sites or web applications.

Active Components Definition, What are Active Components

In electronics, active components are components that can be used to provide power gain in an electronic circuit. This means that the power of their output signal may be more than that of their input signal. This added power is provided by another power source. The most common active components are transistors. One of the basic uses of transistors is in making amplifiers. In a simple transistor amplifier, there's an AC input signal (a current, a voltage or both i.e. a power) that needs to be amplified. A DC power supply is used to provide the additional power needed. This DC supply is said to bias the transistor.

Examples of Active Components

• Transistors >> Bipolar Juction Trasistors >> MOSFETS
• Transistors >> Bipolar Juction Trasistors >> JFETS
• Operational Amplifiers
• Vaccuum Tubes >> Triodes
• Vaccuum Tubes >> Tetrodes
• Vaccuum Tubes >> Pentodes
• Vaccuum Tubes >> Heptodes
• Tunnel Diodes (depending on their bias)

Nonlinear Passive Components

The following devices do not fit the definition generally ascribed to active components, but because of their nonlinear responses, designs, histories, and uses in circuits, are sometimes presented alongside active components in textbooks and educational materials.

• Junction Diodes
• Step recovery Diodes
• Thermionic Diodes
• Thyristors
• Varactor Diodes
• Tunnel Diodes

Adobe Illustrator Definition, What is Adobe Illustrator

Adobe Illustrator is a vector-based drawing program developed and marketed by Adobe Systems.

History of Adobe Illustrator

Adobe Illustrator was first developed for the Apple Macintosh in 1986 (shipping in January 1987) as a logical commercialization of Adobe's in-house font development software and PostScript file format.

Initial Release of Adobe Illustrator

In many ways Illustrator's release was a gamble: the Macintosh did not have high market share, the only printer that could output Illustrator documents was Apple's own LaserWriter (also very new and expensive), and the drawing paradigm of Bezier curves was novel to the mainstream user. Not only did the Macintosh show only monochrome graphics, but display options were basically limited to its built-in 9" monitor. Illustrator helped drive the development of larger monitors for the Macintosh.

Illustrator was a reliable, capable product, however, and its relatively shallow learning curve let users quickly appreciate that the new paradigm was not only better, but finally solved the problem of imprecision from existing programs like MacDraw. It also provided a tool for people who could neither afford nor learn high-end (and perhaps overkill) software such as AutoCAD. Illustrator successfully filled a niche between painting and CAD programs.

Illustrator's power and simplicity derive from the choice of Bezier curves as the primary document element. A degenerate curve provides a line, and circles and arcs (trigonometric shapes) can be emulated closely enough. In a novel twist, Adobe also made Illustrator documents true PostScript files -- if one wanted to print them, one could send them directly to a PostScript printer instead of printing them from Illustrator. Since PostScript is a readable text format, third-party developers also found it easy to write programs that generated Illustrator documents.

Adobe was willing to take risks with Illustrator's user interface. Instead of following Apple's UI guidelines to the letter or imitating other popular Macintosh programs, they made it possible to switch between the various navigation tools (i.e, Zoom and Pan) using various keyboard key combinations.

Adobe Illustrator Versions 2 - 5

Although Adobe developed Illustrator primarily for the Macintosh during its first decade, it sporadically supported other platforms. In the early 1990s, Adobe released versions of Illustrator for NeXT, Silicon Graphics IRIX, and Sun Solaris platforms, but they were discontinued due to poor market acceptance. The first version of Illustrator for Microsoft Windows, version 2.0, was released in early 1989, but it was a flop. The next Windows version, version 4.0, was widely criticized as being too similar to Illustrator 1.1 instead of the Macintosh 3.0 version, and certainly not the equal of Windows' most popular illustration package CorelDraw. (Note that there were no versions 2.0 or 4.0 for the Macintosh.) Version 4 was, however the first version of Illustrator to support editing in preview mode, which did not appear in a Macintosh version until 5.0 in 1993.

Adobe Illustrator Versions 6 - 10

With the introduction of Illustrator 6 in 1996, Adobe made critical changes in the user interface with regards to path editing (and also to converge on the same user interface as Adobe Photoshop), and many users opted not to upgrade. To this day, many users find the changes questionable. Illustrator also began to support TrueType, making the "font wars" between PostScript Type 1 and TrueType largely moot. Like Photoshop, Illustrator also began supporting plug-ins, greatly and quickly extending its abilities.

With true ports of the Macintosh versions to Windows starting with version 7 in 1997, designers could finally standardize on Illustrator. Corel did port CorelDRAW 6.0 to the Macintosh in late 1996, but it was received as too little, too late. Aldus ported FreeHand to Windows but it was not the equal of Illustrator. Adobe bought Aldus in 1994 for PageMaker, and as part of the transaction it sold FreeHand to Macromedia.

With the rise of the Internet, Illustrator was enhanced to support Web publishing, rasterization previewing, PDF, and SVG.

Adobe Illustrator Versions CS (11) & CS2 (12)

Adobe Illustrator is currently (as of March 2007) in version 12 (called CS2 to reflect its integration with Adobe's Creative Suite) and is available for both the Mac OS X and Microsoft Windows operating systems. Illustrator CS was the first version to include 3-dimensional capabilities allowing you extrude or revolve shapes to create simple 3-d objects.

Among the new features included in Illustrator CS2 are Live Trace, Live Paint, a control palette and custom workspaces. Live Trace allows for the conversion of bitmap imagery into vector art. Live Paint allows users more flexibility in applying color to objects, specifically those that overlap.

Adobe Illustrator Versions CS (13)

This version of Adobe Illustrator was announced on March 27, 2007, and shipped on April 16. The Mac version is a universal binary. New features include Live Color, which provides tools for creating color harmonies based on color theory, and the ability to dynamically apply colors to selected objects and shift the tone of an entire illustration at one time. Remapping controls are also provided for reducing the numbers of colors in an artwork. Also new are better integration with Flash, with named symbol instances and dynamic/static text; improved drawing tools and controls; faster runtime performance; an Eraser tool that works on vector objects; a Crop Area tool; and an improved Isolation Mode for groups and symbol definitions.

Adobe Illustrator Branding

Starting with version 1.0, Adobe chose to license Sandro Botticelli's "The Birth of Venus" from the Bettmann Archive and use the portion containing Venus' face as Illustrator's branding image. Warnock desired a Renaissance image to evoke his vision of Postscript as a new Renaissance in publishing, and Adobe employee Luanne Seymour Cohen, who was responsible for the early marketing material, found Venus' flowing tresses a perfect vehicle for demonstrating Illustrator's strength in tracing smooth curves over bitmap source images. Over the years the rendition of this image on Illustrator's splash screen and packaging became more stylized to reflect features added in each version.

The image of Venus was replaced in Illustrator CS (11.0) and CS2 (12.0) by a stylized flower to conform to the Creative Suite's nature imagery. In CS3, Adobe changed the suite branding once again, to simple colored blocks with two-letter abbreviations, resembling a periodic table of elements. Illustrator was represented by the letters Ai against an orange background.