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Lesson 2 Serial devices
Objective Describe serial devices supported by Red Hat Linux.

Linux Serial Devices

Red Hat Linux supports common serial devices, such as:
  1. Modems
  2. Mice
  3. Serial terminals
Serial devices attach to a computer through an external interface, either a 9-pin or 25-pin RS-232 connector, known as a serial port. Alternatively, an internal device might be assigned a logical serial port, through the computer's BIOS.

RS-232 connectors

External and internal devices, although of the same type and similar functionality, might not have the same characteristics. For example, external and internal modems both connect two computers over a phone line. External modems are completely separate devices that operate without the support of the computer's CPU. Internal modems usually cannot function as standalone devices and require the operating system to assist them. Linux supports all external modems, but only a handful of internal modems.
  1. BIOS: Basic Input and Output System. The BIOS is responsible for providing a standard interface to the computer hardware. An operating system writes to a particular BIOS specification, rather than worrying about the details for all supported hardware.
  2. The getty daemon: Actual hardwired terminals are almost never seen anymore. The idea of a connected terminal (or serial device such as a mouse) remains, however.
The getty daemon[1] and its variants support serial communications under Linux. Commonly used protocols over serial lines include PPP and SLIP. The getty daemon allows users to log in to a Linux station using a serial device, which is allocated a terminal (tty). getty assigns each user a different tty session to communicate between themselves and the machine.
The next lesson explains how to administer serial ports.

[1] Daemon : A daemon is a program that waits for a request from another program. The daemon then performs the desired action, such as creating an http session, or opening and maintaining a communications socket. Some common daemons include httpd, telnetd, and ftpd.