CompTIA A+® Certification All-In-One For Dummies®, 2nd Edition

2.3. Communicating with Modems and Network Adapters

In this section, you find out about installing modems and network cards that allow computer systems to communicate with other systems on the network.

2.3.1. Working with modems

A modem is a communication device that modulates, or converts, the digital signal from the computer into an analog signal so that it can travel over an analog line, such as telephone wire. The signal is then demodulated back into a digital signal at the modem on the receiving system. The process of modulating and demodulating is where the amalgam word modem comes from.

A modem allows a computer to send data over an analog line and is useful when you want to dial up another computer over a phone line or access the Internet.

2.3.1.1. Modem characteristics

A modem is either internal or external:

• An internal modem is installed in an expansion slot within the computer housing as either an older ISA card or, more popular today, a PCI card.

• An external modem sits on the desk beside the computer and plugs into the computer's serial port.

Both internal and external modems plug into a telephone jack via a standard telephone cable.

Another very important characteristic of the modem is its speed. The speed of the modem is measured in bits per second (bps) — and like anything else, the more bits the better! When it comes to modem speed, you're looking at 56 Kbps (56,000 bps) as the standard. This is known as a 56K modem.

2.3.1.2. AT commands

For the A+ exam, you ...