Modem
Modem is short for Modulator/Demodulator. Modulation refers to the conversion of a digital signal to an analog signal, and demodulation reverses this process. Your computer is digital, while the phone lines that you want to communicate over are analog. In order to allow the digital signal to be passed over the analog lines, you must use a modem.
Modems allow computers to be placed anywhere there are phone lines, and still communicate with each other. Prior to modems, there was no low-cost means of connecting distant computers together; your only choice was an expensive dedicated leased phone line from the Telco. The speeds at which modems operate have been increasing since their invention. They started with transfer rates of 300 bps (bits per second) and have moved up to 115 Kbps.
Today, where modems were traditionally used, they are often replaced by other remote connectivity options, such as ADSL (Asymmetric Digital Subscriber Line), ISDN (Integrated Services Digital Network), and broadband cable. Each of these systems has a device which is called a modem to connect your Ethernet network card to the data network. ADSL and broadband cable send the signals over analog networks and modulate your data signal to previously unused frequencies. ISDN is digital on both sides of the connection, so there is no modulation taking place. The correct term for this device would be a TA (Terminal Adapter) and not a modem.
Standard modems connect to your computer through the serial port and can be synchronous or asynchronous. Most modems that are purchased for a computer are asynchronous.
Ports
Sailing ports provide a location for ships to load and unload goods from one location to another. On your computer, ports act as connection points for cables, which allow for the transfer of data between your computer and another device. Several different types of connectors and cables are used to join devices together. Although the list of devices that communicate through the different types of ports is limitless, some of the basic types of ports and their uses are listed in Table below.
Basic Types of Ports| Port | Use |
|---|---|
| Serial | Connects serial devices such as modems to your computer. |
| Parallel | Connects parallel devices such as printers to your computer. |
| Video | Connects a monitor to your computer. |
| USB | Connects various types of devices to your computer. Devices that used other ports in the past are increasingly being converted to use USB ports. Devices that use this port include printers, modems, mice, keyboards, and scanners. |
| Keyboard | Connects a keyboard to your computer. |
| Mouse | Connects a mouse to your computer. |