2.3 Hardware Components
2.3.13 Modems and network interface cards (NICs)
A modem is the primary way to connect to the Internet with Windows 9x through a dial-up networking connection. The word "modem" is actually an acronym for modulator/demodulator. A modem is, in essence, a device that converts the digital data used by computers into analog signals that are suitable for transmission over a telephone line and converts the analog signals back to digital signals at the destination. A computer not connected to a network by some other means, such as a NIC, will typically have a modem card installed. A modem plugged to one of the expansion slots inside a PC is known as an internal modem. Such a modem usually has two types of connectors called registered jack type 11, more commonly called RJ-11 jacks. One is for the phone line while the other is used to attach a traditional telephone handset.

These modems come in the form of expansion cards also known as modem cards. The modem card handles all the data transmission on the computer serial port, with the help of a special chip called the Universal Asynchronous Receiver Transmitter (UART) chip. Almost every PC sold today will have a 16550 UART chip inside because people want a high-speed connection to the Internet. The number preceding UART, 16550 represents a generational evolution of these chips, typically associated with a PC generation. There are three generations:

  • 8250 – The original chip in XTs, it has only a one-byte buffer (temporal storage for data as it is sent bit-by-bit out a serial line such as a phone line).
  • 16450 – Introduced with the AT systems, it has a two-byte buffer.
  • 16550 – Most popular with Pentium computers, it has a so-called first in, first out (FIFO) buffer that effectively eliminates data overrun, a common problem that occurs when a system sends data to the port faster than it can be processed.

The major difference in the different UART chips is the speed at which they can enable data transmission. Notable advanced UART versions include the 16450 and 16550. The 16450 was the 16-bit improvement of the 8250, while the 16550 was a high-performance UART with an on-board 16-byte buffer.

More about modems and their role in internet connectivity is in Chapter 8, "Networking Fundamentals".

Network Interface Card (NIC)
A Network Interface Card (NIC), also known as a network adapter, is used to connect a local computer to a group of other computers so they can share data and resources in a networked environment. All network interface cards on a local area network are designed to use Ethernet, Token Ring, or another similar protocol to communicate with other machines in the network.

As its name implies, NICs come in the form of expansion cards (PCI or ISA) that can be installed in one of the computer expansion slots. The network cable plugs to the computer through the adapter card or NIC. This is possible due to a connector type known as the RJ-45 connector. This connector is very similar to the RJ-11, which was discussed earlier, except that it has 8 wires inside (instead of 4 wires for the RJ-11 phone jack).

With the NIC card, the RJ-45 jack is used with Unshielded Twisted Pair (UTP) LAN cabling, while another type of connector, the British Naval Connector (BNC) is provided for coaxial cable connections. Network cabling (networking media), as well as NICs are discussed in more detail in Chapter 8 "Networking Fundamentals."