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Short for modulator-demodulator. A modem is a device or program that enables a computer to transmit data over, for example, telephone or cable lines. Computer information is stored digitally, whereas information transmitted over telephone lines is transmitted in the form of analog waves. A modem converts between these two forms. Fortunately, there is one standard interface for connecting external modems to computers called RS-232. Consequently, any external modem can be attached to any computer that has an RS-232 port, which almost all personal computers have. There are also modems that come as an expansion board that you can insert into a vacant expansion slot. These are sometimes called onboard or internal modems. While the modem interfaces are standardized, a number of different protocols for formatting data to be transmitted over telephone lines exist. Some, like CCITT V.34, are official standards, while others have been developed by private companies. Most modems have built-in support for the more common protocols -- at slow data transmission speeds at least, most modems can communicate with each other. At high transmission speeds, however, the protocols are less standardized. Aside from the transmission protocols that they support, the following characteristics distinguish one modem from another: bps : How fast the modem can transmit and receive data. At slow rates, modems are measured in terms of baud rates. The slowest rate is 300 baud (about 25 cps). At higher speeds, modems are measured in terms of bits per second (bps). The fastest modems run at 57,600 bps, although they can achieve even higher data transfer rates by compressing the data. Obviously, the faster the transmission rate, the faster you can send and receive data. Note, however, that you cannot receive data any faster than it is being sent. If, for example, the device sending data to your computer is sending it at 2,400 bps, you must receive it at 2,400 bps. It does not always pay, therefore, to have a very fast modem. In addition, some telephone lines are unable to transmit data reliably at very high rates. voice/data: Many modems support a switch to change between voice and data modes. In data mode, the modem acts like a regular modem. In voice mode, the modem acts like a regular telephone. Modems that support a voice/data switch have a built-in loudspeaker and microphone for voice communication. auto-answer : An auto-answer modem enables your computer to receive calls in your absence. This is only necessary if you are offering some type of computer service that people can call in to use. data compression : Some modems perform data compression, which enables them to send data at faster rates. However, the modem at the receiving end must be able to decompress the data using the same compression technique. flash memory : Some modems come with flash memory rather than conventional ROM, which means that the communications protocols can be easily updated if necessary. Fax capability: Most modern modems are fax modems, which means that they can send and receive faxes. To get the most out of a modem, you should have a communications software package, a program that simplifies the task of transferring data.
Definition: In computer networking, a NIC provides the hardware interface between a computer and a network. A NIC technically is network adapter hardware in the form factor of an add-in card such as a PCI or PCMCIA card. Some NIC cards work with wired connections while others are wireless. Most NICs support either wired Ethernet or WiFi? wireless standards. Ethernet NICs plug into the system bus of the PC and include jacks for network cables, while WiFi? NICs contain built-in transmitters / receivers (transceivers). In new computers, many NICs are now pre-installed by the manufacturer. All NICs feature a speed rating such as 11 Mbps, 54 Mbps or 100 Mbps that suggest the general performance of the unit. Also Known As: NIC also stands for Network Information Center. For example, the organization named "InterNIC" is a NIC that provides information to the general public on Internet domain names.
An expansion board that enables a computer to manipulate and output sounds. Sound cards are necessary for nearly all CD-ROMs and have become commonplace on modern personal computers. Sound cards enable the computer to output sound through speakers connected to the board, to record sound input from a microphone connected to the computer, and manipulate sound stored on a disk. Nearly all sound cards support MIDI, a standard for representing music electronically. In addition, most sound cards are Sound Blaster-compatible, which means that they can process commands written for a Sound Blaster card, the de facto standard for PC sound. Sound cards use two basic methods to translate digital data into analog sounds: FM Synthesis mimics different musical instruments according to built-in formulas. Wavetable Synthesis relies on recordings of actual instruments to produce sound. Wavetable synthesis produces more accurate sound, but is also more expensive.
The graphics card plays an essential role in the PC. It takes the digital information that the computer produces and turns it into something human beings can see. On most computers, the graphics card converts digital information to analog information for display on the monitor; on laptops, the data remains digital because laptop displays are digital.