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3.2. Objective 3: Configure Modems and Sound CardsModems and sound cards, while non-essential, are two of the most common pieces of hardware installed in a Linux system; unfortunately, they are also two of the most problematic to configure. This Objective covers the tasks required to complete modem and sound card configuration. 3.2.1. ModemsA modem (a word derived from modulate and demodulate) is that familiar device that modulates a digital signal into an analog signal for transmitting information via telephone lines. A modem on the other end of the connection demodulates the signal back into its digital form. Modems can also add digital compression and error correction capabilities to increase speed and reliability. 3.2.1.1. Modem typesModems are serial devices, where data enters and exits one bit at a time. Traditionally, modems were external devices attached via cable to industry standard RS-232 serial ports, such as those still found on most PCs. This arrangement continues to work well, because the data rates of telephone connections are still below the maximum rate of the serial ports. As a result, external devices yield solid performance. Internal modems (ISA or PCI bus cards that reside inside a PC) were developed to reduce costs associated with external modems (namely, the case, power supply, and shipping charges) and offer the same functionality as an external modem. Most internal modems present themselves to the PC as a standard serial port. In a typical PC with the first two serial ports built in (/dev/ttyS0 and /dev/ttyS1), an internal modem will appear as the third port (/dev/ttys2). This means that from a programming point of view, internal modems are indistinguishable from external modems. While there is some variation in modem configuration across manufacturers, the differences are small, and most serial-port-style modems will work with Linux. One exception is a modem designed specifically to work with the Windows operating system. These so-called winmodems rely on the CPU and a special software driver to handle some of the communications processing, and thus lack the full hardware capabilities of standard modems. As such, winmodems are not compatible with Linux unless a Linux-specific driver is available. Information on such support is available from http://www.linmodems.org. 3.2.1.2. Modem hardware resourcesAs with any add-on card, particularly cards configured manually, the user must be careful to avoid resource conflicts. Modems shouldn't cause much difficulty since they're simple serial ports. However, you should confirm that the correct interrupt and I/O addresses are set on your modem. If the modem shares an interrupt with another serial port, that port cannot be used at the same time as the modem. 3.2.2. Sound DevicesNearly every laptop and desktop PC shipped today includes a sound device. Fortunately, Linux sound drivers are available for most sound chipsets, including the old industry standard chipset defined by Creative Labs with its SoundBlaster series. Today's PC is typically built with AC97 chipset sound devices built in or include a PCI device with similar chipset. For cards that don't work with the native kernel modules, you may have to use a tool such as sndconfig or for more ancient ISA hardware, isapnp. In either case, part of the configuration for a sound card involves correctly specifying the sound card's resources to the sound driver.
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