SearchEngines
Written by Charles Knight, AltSearchEngines editor
Internet search tools fall into two camps：search engines，such as HotBot and AltaVista，and online directories，such as Yahoo and Lycos．The difference between the two is related to how they compile their site listings．Of course，there are exceptions to every rule．Some search utilities，such as Ask Jeeves，combine the search engine and directory approaches into a single package，hoping to provide users with the best of both worlds．
In directory-based search services，the Web site listings are compiled manually．For example，the everpopular Yahoo dedicates staff resources to accept site suggestions from users，review and categorize them，and add them to a specific directory on the Yahoo site．
You can usually submit your Web site simply by filling out an online form．On Yahoo，for example，you'll find submission information at
www.yahoo.com/docs/info/include.html．Because human intervention is necessary to process，verify，and review submission requests，expect a delay before your site secures a spot in a directory-based search service．
On the flip side，search engines completely automate the compilation process，removing the human component entirely．
A software robot，called a spider or crawler，automatically fetches sites all over the Web，reading pages and following associated links．By design，a spider will return to a site periodically to check for new pages and changes to existing pages．
Results from spidering are recorded in the search engine’s index or catalog．Given the wealth of information available on the Internet，it is not surprising that indexes grow to very large sizes．For example，the AltaVista index has recently been increased to top out at 350 million pages．This may seem like a mammoth number，but by all estimates it still represents less than 35 percent of all pages on the Web．
Because of the depth and breadth of information being indexed，there is usually a delay，sometimes up to several weeks，between the time a site has been“spidered”and when it appears in a search index．Until this two-step process has been completed，a site remains unavailable to search queries．
Finally，the heart of each search engine is an algorithm that matches keyword queries against the information in the index，ranking results in the order the algorithm deems most relevant．
Because the spiders，resulting indexes，and search algorithms of each search engine differ，so do the search results and rankings across the various search engines．This explains why a top 10 site in HotBot may not appear near the top of Alta Vista when the same keyword search criterion is entered．
In addition，many，but not all，search utilities also reference metatags—invisible HTML tags within documents that describe their content—as a way to control how content is indexed．As a result，proper use of metatags throughout a site can also boost search engine ranking.
Advanced Wireless LAN Standard
With portable computers and wireless LANs,users can enjoy greater productivity while away from their desks ,whether they are in conference rooms, public areas or remote offices.
Until recently , however,wireless LANs were too slow for most enterprise applications.based on the IEEE 802.11 standdrd,they ran at 1M to 2M bit/sec.
Now a new high -rate extension to the standard ,802.11b, lets wireless networks support data rates to 11M bit/sec.
Ratified in 1997 ,the original 802.11 standardunited the wireless industury by defining a low-level protocol architecture that worked with conventional upper-layer enterprise protocol stacks . also, 802.11 maintained compatibility with the three most popular radio transmission types: direct sequence spread spectrum,frequency-hopping spread spectrum,and infrared.
Essentially,this new architecture added intelligence at the medium access control(MAC) layer 2 and at the physical (PHY) layer 1, fosteing cooperation between the two layers in performing the critical tasks involved with initiating and maintaining wireless communi-cations.
For instance ,to ensure reliability of the wireless link ,MAC and PHY work together to determine if a clear path exists before they start a transmission.
During transmission, they employ special collision -avoidance and arrival-acknowledgment techniques that are not required in wired ethernet LANs.
In september 1999,the IEEE approved a new designation, known as 802.11.intended to retain the error-correction,security,powermanagement and other advantages of the original , a key ingredient-a thchnique for increasing bandwidth to 11M bit/sec.
Called complementary code keying (CCK) the technique works only in conjunction with the DSSS technology sprcified in the original standard . it does net work with frequency-hopping or infrared transmissions.
What CCK does is apply sophisticated mathematical formulas to the DSSS codes, a permitting the code to represent a greater volume of informitter is now able to send multiple bits of information with each DSSS code ,enough to make possible the 11M bit /sec in the original standard .
The 802.11b standard benefits users by delivering wireless ethernet speeds of 11M bit/sec that can reliably support everyday business applications,e-mail,internet and server network access.
With support from the new wireless ethernet from the new wireless ethernet compatibility alliance ,founded by 3com,lucent,nokia and several other companies in the wireless LAN business,the new standard will also promise certified interoperability across multivendor platforms.
Finally, the 802.11b standard serves as a clamoring for a simplified wireless LAN landscpape.
Vendors can now focus on a single ,high-speed standard , and users can cut through the clutter of wireless options by fovusing on a standard that delivers multibvendor interoperability and the performance to meet their application needs. You have probably seen an increase in the amount of "junk mail" which shows up in your email box, or on your favorite newsgroup(新闻组). The activities of a small number of people are becoming a bigger problem for the Internet. We have been actively engaged in fighting spam for years. Since we presented this site to the public in 1996, we have been pleased to be referenced as one of the best anti-spam sites on the net. Help fight spam to keep the Internet useful for everyone. Take advantage of the information we've gathered to make your own experience on the Internet better.
Understand Kerberos In Depth
Kerberos was developed at MIT in 1998s. it was named after the three-headed watchdog in classical Greek mythology that guards the gates to Hades .the name is apt because Kerberos is a three-way process , depending on a thrid-party service called the Key distribution center(KDC) to verify one computer's identity to another and to set up encryption keys for a secure connection between them .basically,kerberos works because each computer shares a secret with the KDC, which has two components:a Kerberos authentication server and a ticket-granting server , it a KDC doesn't know the requested target server, it refers the authentication transaction to another KDC that does .Kerberos is a network authentication protocol that allows one computer to prove its identity to another across an insecure network through an exchange of encrypted messages. once identity is verified, kerberos provides the two computer with encryption keys for a secure communication session. kerberos authenticates the identity and encrypts their communications through secret-key cryptography.
Multimedia
The answer is neither simple nor easy. Multimedia is the combination of computer and video technology. Multimedia really just two media sound and pictures, or in today's term, audio and video. Multimedia itself has its binary aspects. As with all modern technologies, it is made from a mix of hardware and software, machine and ideas. More importantly, you can conceptually divide technology and function of multimedia into control systems and information. The enabling force behind multimedia is digital technology. Multimedia represents the convergence of digital control and digital media---the PC as the digital control system and the digital media being today's most advanced form of audio and video storage and transmission. In fact, some people see multimedia simply as the marriage of PCs and video. PC power has reached a level close to that needed for procession television and sound data streams in real time, multimedia was born. Multimedia PC needs to be more powerful than mainstream computer---at least the multimedia PC defines the mainstream. Among contemporary PCs, about the only things that separate an ordinary computer from multimedia are a soundboard and a CD- ROM driver. The CD serves as multimedia 's chief storage and exchange medium. Without the convenient CD, the PC industry would lack a means of distributing the hundreds of megabytes of audio, visual, and textual data that make up today's multimedia titles. Without CD, you couldn't buy multimedia because publishers have no way of getting it to you.
So what is multimedia? By now you should agree that multimedia isn't any one thing but a complex entity that involves the many things: hardware, software, and the interface where they meet. But we've forgotten the most important thing that multimedia involves: you. Yeah, sure. With multimedia, you don' t have to be a passive recipient. You can control. You can interact. You can make it do what you want it to do. It means you can tailor a multimedia presentation to your own needs. You can cut through the chaff and dig directly into the important data in a report, pull together reports and video clips from around the world that interest you. That's the strength of multimedia and what distinguishes it from traditional media like books and television.
What does multimedia do? It presents information, shares ideas and elicits emotions. It enables you to see, hear, and understand the thoughts of others. In other words, it is a form of communication.
The @ Symbol
That little "a" with a circle curling around it that is found in email addresses is most commonly referred to as the "at" symbol.
Surprisingly though, there is no official, universal name for this sign. There are dozens of strange terms to describe the @ symbol.
Before it became the standard symbol for electronic mail, the @ symbol was used to represent the cost or weight of something. For instance, if you purchased 6 apples, you might write it as 6 apples @ $1.10 each.
With the introduction of e-mail came the popularity of the @ symbol. The @ symbol or the "at sign" separates a person's online user name from his mail server address. For instance,
joe@uselessknowledge.com. Its widespread use on the Internet made it necessary to put this symbol on keyboards in other countries that have never seen or used the symbol before. As a result, there is really no official name for this symbol.
The actual origin of the @ symbol remains an enigma.
History tells us that the @ symbol stemmed from the tired hands of the medieval monks. During the Middle Ages before the invention of printing presses, every letter of a word had to be painstakingly transcribed by hand for each copy of a published book. The monks that performed these long, tedious copying duties looked for ways to reduce the number of individual strokes per word for common words. Although the word "at" is quite short to begin with, it was a common enough word in texts and documents that medieval monks thought it would be quicker and easier to shorten the word "at" even more. As a result, the monks looped the "t" around the "a" and created it into a circle-eliminating two strokes of the pen.
ARPAnet
A wide area network (WAN) .A network that connected Department of Defense research sites across America. Created in 1969 with funding from the Advanced Research Projects Agency (ARPA) .Undergoing constant research and development in the early-to mid-1970s,ARPAnet served as the test bed for the development of TCP/IP( the protocols that make the Internet possible ).A Major goal of the ARPAnet project was to increase the military's command and control capability by enabling communication across a variety of physically dissimilar media ,including satellites .An allied goal was to create a robust network capable of withstanding outages ,such as those that might result from a nuclear exchange .ARPAnet met these objectives ,but it also surprised its creators :It was found in short order that most ARPAnet users preferred to use the network for communication ,such as electronic mail and discussion groups .Initially ,the ARPAnet was available only to government research institutes and to universities holding Department of Defense (DoD) research contracts .In 1983,ARPAnet was divided into a high-security military network (Milnet )and an ARPAnet that was recast as a research and development network .Although it formed the foundation of the Internet ,it was decommissioned in 1990.
Alias
An alternative name for software ,hardware ,or user that points to the real name .For example ,on your computer ,you can name your hard drive Thelma instead of the insipid manufacturer identification ,like Q540.An alias applied to a software program will allow it to be opened via different names or icons in different windows .Most E-mail providers allow you to choose an alias in place of your real user name on the network ,so a message addressed to
joesmith@smith.com will get to a user registered as mjsmith .Alias is a secondary or symbolic name for a file ,a collection of data ,or a computer device .In a spreadsheet ,a range name ,such as Income ,is an alias for a range ,such as A3..K3.In networks ,group aliases provide a handy way to send electronic mail to two or more people simultaneously.
Base Address：
The part of a two-part memory address that remains constant and provides a reference point from which the location of a byte of data can be calculated. a base address is accompanied by an offset value that is added to the base to determine the exact location(the absolute address)of the information. the concept is similar to a street address system . for example, "2010 main street " plus an offset(10from the beginning of the block ).base address are known as segment address in IBM pcs and compatibles; data in these computers is identified by its position as a relative offset the start of the segmentArtificial Life
A scientific research area devoted to the creation and study of computer simulations of living organisms .Computer viruses have forced a renewal of the debate on the definition of life .Besides forcing us to re-examine our definition of life ,artificial life research may create more effective technology .By applying artificial life concepts to real-life problems ,we can program computer-generated solutions to compete
Magical Electronic Ink and Paper
Cambridge，Mass.-based E Ink Corp．is a leader in the development of electronic ink and “paper”that could replace newspapers and books as we know them today．
The use of electronic ink and two-way wireless communication could lead to the creation of electronic books that will renew themselves with new selections when readers are finished with the current book——or newspapers that update themselves with the latest news while being read．
Electronic ink，as devised by E Ink，is a clear，liquid plastic in which there are microcapsules that contain white chips in a blue dye．The microcapsules are suspended in a substance similar to vegetable cooking oil．The white chips are negatively charged so they react to electrical stimulus．
This ink can be spread on any surface——from walls to computer screens——says Russell Wilcox，vice president and general manager at E Ink．However，the writing surface would look similar to a very thin laptop display screen with a clear surface on the front and circuitry on the back．
A positive charge applied on the top surface of the ink will allow the white to show，making the surface as white as a sheet of paper．If the charge moves to the bottom，the dark particles will show，giving the appearance of blue ink．Electronic ink uses less power than a PalmPilot，and the message remains displayed even after the power is turned off． The ultimate goal is for the electronic pages to look and feel like paper．However，for the foreseeable future，these new books are likely to be bulkier than paperback books．
Electronic ink will have interactive qualities，although E Ink isn't sure people will be able to write with it for a while——they will mainly receive messages．Xerox Corp．is also working on a technology that could replace paper as portable，renewable reading matter．
The Xerox technology is called Gyricon．It's composed of a silicon rubber compound with the thickness and flexilility of poster board．The Gyricon sheets have thousands of plastic balls suspended in oil．Each ball is black on one side and white on the other and together they act as pixels to display images．Images can be updated much the same way as with a monitor．The beads are embedded in a large sheet，with each microcapsule suspended in oil to allow the beads to rotate in their orbits，says Robert Sprague，manager of the document hardware lab and electronic paper projects at Xerox's Palo Alto Research Center．The paper could be powered by a matrix of transistors，such as those in laptop computer screens．Gyricon uses reflective light，like real paper，so it would use less electricity．
A Gyricon book will eventually be connected with a wireless device that will enable a reader to download content from the Internet．
Xerox will also make the Gyricon interactive，so a user could write on it and reuse it．
