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Demodulation
Demodulation is the process of decoding an analog signal into digital data. When data is transferred over phone lines, a modem modulates the data into audible tones "carried" on frequencies between 0 Hz and 4 KHz. Once the data reaches its intended destination, another modem demodulates the signal back into digital data. Cable TV networks also use modulation techniques to transfer data. But instead of audible tones, cable has sophisticated digital modulation schemes to greatly increase the amount of data that can be sent.
DHTML
dynamic HTML
The W3C may not have an official definition for it, but dynamic HTML combines HTML, style sheets, and scripts to make Web pages more interactive. It sounds great. But while both Microsoft Internet Explorer 4.0 and Netscape Communicator 4.0 support dynamic HTML features, they do so in different--and incompatible--ways. The companies say they will work to make their browsers compatible with whatever specification the W3C finally decides upon. However, the browsers may be in their fifth generation before users see a concrete standard.
Digital Certificate
Citing concerns about security, many people are still wary of online transactions. In an attempt to assuage those fears, software vendors, security specialists, and online vendors have developed the concept of digital certificates. A digital certificate is a password-protected file that includes a variety of information: the name and email address of the certificate holder, an encryption key that can be used to verify the digital signature of the holder, the name of the company issuing the certificate, and the period during which the certificate is valid. Certificate authorities (CAs) gather information about a person or company and then issue certificates. These certificates can be used as online identification, much in the same way a driver's license can verify your identity in the physical world. If an email message or order form comes through with an attached digital certificate, the recipient can be more confident that the document is genuine. Several technologies (including SET, SSL, and Authenticode) are currently competing for market share, each hoping to become the certificate of choice.
Digital Signature
Forgery is a growing concern among Netizens. After all, who's to say that a message with your name on it is really from you and not somebody pretending to be you? Digital signatures are a means of proving that a file or email message belongs to a specific person, much as a driver's license proves identity in real life. Digital signatures have the added benefit of verifying that your message has not been tampered with. When you sign a message, a hash function--a computation that leaves a specific code, or "digital fingerprint"--is applied to it. If the fingerprint on the recipient's message doesn't match the original fingerprint, the message has been altered.
Digital signatures are often used in combination with strong-encryption software to create a secure channel of communication, in which both privacy and identity are protected.
Domain Name
Looking for a domain name? You'll find it to the right of the @ sign in an email address, or about ten characters into a URL. CNET's domain name is cnet.com. The domain name of daemous@pentagon.io.com is io.com. Domain names are issued by the National Science Foundation (NSF), and they come with different extensions based on whether the domain belongs to a commerical enterprise (.com), an educational establishment (.edu), a government body (.gov), the military (.mil), a network (.net), or a nonprofit organization (.org). Some domains use a geographical notation too (such as the San Francisco, California-based well.sf.ca.us).
Duplex
If you have a printer that can print on both sides of a sheet of paper, it's duplex. If you have a communications line that lets you send and receive data (or talk and listen) at the same time, it's duplex. If you use a cheap speakerphone, you'll notice that as soon as it picks up any noise at your end, it cuts off whatever was being said by the person on the other end. That speakerphone is not duplex.