09-A.1.1: Supported Linux Devices (cont'd)

Audio and Video Devices

Audio connectors and video connectors are electrical or optical connectors for carrying audio and video signals. Audio interfaces and video interfaces define physical parameters and interpretation of signals. For digital audio and digital video, this can be thought of as defining the physical layer, data link layer, and most or all of the application layer. For analog audio and analog video these functions are all represented in a single signal specification like NTSC or the direct speaker-driving signal of analog audio. Physical characteristics of the electrical or optical equipment includes the types and numbers of wires required, voltages, frequencies, optical intensity, and the physical design of the connectors. Any data link layer details define how application data is encapsulated (for example for synchronization or error-correction). Application layer details define the actual audio or video format being transmitted, often incorporating a codecs not specific to the interface, such as PCM, MPEG-2, or the DTS Coherent Acoustics codec. In some cases, the application layer is left open; for example, HDMI contains an Ethernet channel for general data transmission.

Some types of connectors are used by multiple hardware interfaces; for example, RCA connectors are defined both by the composite video and component video interfaces, but DVI is the only interface that uses the DVI connector. This means that in some cases not all components with physically compatible connectors will actually work together.

Some of these connectors, and other types of connectors, are also used at radio frequency (RF) to connect a radio or television receiver to an antenna or to a cable system; RF connector applications are not further described here. Analog A/V connectors often use shielded cables to inhibit radio frequency interference (RFI) and noise.

For efficiency and simplicity, the same codec or signal convention is used by the storage medium. For example, VHS tapes can store a magnetic representation of an NTSC signal, and the specification for Blu-ray Discs incorporates PCM, MPEG-2, and DTS. Some playback devices can re-encode audio or video so that the format used for storage does not have to be the same as the format transmitted over the A/V interface (which is helpful if a projector or monitor cannot handle a newer codec).

Printers

Linux supports numerous printer interfaces. Over the life of Linux some interfaces that used to be popular for connecting printers have disappeared.

Parallel
A parallel printer interface works by sending an 8-bit information stream to the printer. The parallel printer cable has a DB-25 connector to connect to the computer and a 36-pin Centronics connector to the printer interface. Data integrity decreases if the cable gets too long, therefore the maximum length of the parallel cable is usually limited to 10 feet.

Serial
A serial printer interface sends the data to the printer one bit at a time. Serial printers are rarely used these days, however some dot matrix printers that are still found in certain applications use this interface.

Small Computer System Interface (SCSI)
There are not very many printers which use a SCSI interface. These printers are pretty much obsolete due to newer, faster printer interfaces. Most of the current printers being manufactured make use of the much higher speed of newer interfaces.

Universal Serial Bus (USB)
The USB port is the most common port available on PCs today. It is an excellent interface and is used on printers and desktop printers/scanners combos. USB is much faster than most of the other types of printer interfaces.

Network
Today most printers come with a built-in network adapter or can also have one fitted into them. Network printers are directly attached to the local network. The printer uses a standard network cable with a standard RJ-45 connector.

Wireless
Many printers nowadays provide the capability to use wireless connections that support 802.11, or Bluetooth. The main advantage of wireless connections is that there are no wires. The disadvantage is that there is a limit to the range of the network coverage.

Network Interface

A network interface controller (NIC, also known as a network interface card or network adapter) is a computer hardware component that connects a computer to a computer network. Most computers have at least one NIC, although it is entirely possible for Linux systems to have multiple network adapters; this is especially true of specialized Linux servers, such as firewalls.

Network controllers were originally implemented as expansion cards that plugged into a computer bus. The low cost and ubiquity of the Ethernet standard means that most new computers have a network interface controller built into the motherboard. Newer server motherboards may have multiple network interfaces built-in. The Ethernet capabilities are either integrated into the motherboard chipset or implemented via a low-cost dedicated Ethernet chip. A separate network card is typically no longer required unless additional independent network connections are needed or some non-Ethernet type of network is used. A general trend in computer hardware is towards integrating the various components of systems on a chip, and this is also applied to network interface cards.

GPIO

Stands for "General Purpose Input/Output." Some GPIOs have a primary function whereas other GPIOs are a convenient "accessory" to some other primary function.

GPIOs are used in a diverse variety of applications, limited only by the electrical and timing specifications of the GPIO interface and the ability of software to interact with GPIOs in a sufficiently timely manner.

GPIOs typically employ standard logic levels and cannot supply significant current to output loads. When followed by an appropriate high-current output buffer (or mechanical or solid-state relay), a GPIO may be used to control high-power devices such as lights, solenoids, heaters, and motors (e.g., fans and blowers). Similarly, an input buffer, relay or opto-isolator is often used to translate an otherwise incompatible signal (e.g., high voltage) to the logic levels required by a GPIO.

Adapted from:
"Audio and video interfaces and connectors" by Multiple Contributors, Wikipedia is licensed under CC BY-SA 3.0"
Network interface controller" by Multiple Contributors, Wikipedia is licensed under CC BY-SA 3.0
"General-purpose input/output" by Multiple Contributors, Wikipedia is licensed under CC BY-SA 3.0