Serial interface
　　Serial interface, called as serial port for short, namely COM interface, is a kind of extension interface complying with the serial communication protocol. Serial port appeared around 1980, with the data transfer rate of 115kbps-230kbps. Generally serial port is used to connect such equipment as mouse, external Modem, old-styled cameras and tablets, etc, at present, some new main boards have excluded such interfaces.

Parallel Interface
　　Parallel interface, called parallel port for short, is also a kind of LPT interface and a kind of extension interface complying with the parallel communication protocol. The data transfer rate of parallel port is 8 times faster than that of serial port, the data transfer rate of standard parallel port is 1Mbps, generally used to connect printer and scanner, etc. Therefore parallel port is also called printer port.

USB interface
　　USB is abbreviated from Universal Serial Bus, and the Chinese meaning is “All-purpose 串行总线”. It is not a kind of new bus standard, but an interface technology applied in PC domains. USB was put forward jointly by several companies at the end of 1994 like Intel, Compaq, IBM and Microsoft, etc. However, it is only widely used in the recent years. After USB V0.7 was released on November 11th, 1994, versions of USB have been developed for years and now come to Version 2.0, and USB has become the standard extension interface at present configured in computers. Now the main boards mainly apply USB1.1 and USB2.0, All versions of USB are well compatible with one another. USB uses a 4-needled plug as the standard plug, adopts the form of daisy chain to connect all external equipment, 127 at the maximum, and will not damage the bandwidth. USB will only work if supported by the main unit hardware, operating system and external configuration. At present, the main boards generally adopts the control chipsets supporting USB functions, and the main boards are mounted with USB interface sockets. In addition to the sockets on the backboards, the main boards have reserved USB pins that may be connected by the connection line to the front of crate as the superposed USB interface for use. (Caution: Please carefully read the main board instructions and connect the line as per the chart prior to connecting the connection line to prevent from the damages to device caused by improper connection). Further, USB interface may be connected to two computers via the dedicated USB connection lines and extend to more interfaces with the hub. USB characterizes rapid transmission rate, (that for USB1.1 is 12Mbps and that for USB2.0 is 480Mbps), handy use, supporting hot swap, flexible connection and independent power supply, etc. It may be connected to the mouse, keyboard, printer, scanner, camera, flash Memory, MP3 player, cell phone, digital camera, movable hard disk, external floppy disk drive, USB network card, ADSL Modem and Cable Modem, etc., almost all kinds of external device.

IEEE 1394
　　IEEE 1394 was formerly called Firewire (live line), and is a kind of transmission interface developed in 1986 by Apple Computer, Inc. for hi-speed data transmission. It was recognized formally in 1995 by Institute of Electrical and Electronics Engineers/ IEEE and became the formal standard. IEEE1394, Firewire and i.LINK frequently seen by us actually refer to this stand. Generally speaking, it is called IEEE1394 in PC field, i.LINK in the field of electric consumer goods, i.LINK in most cases. While it is called Firewire in Apple computers produced at the very beginning. IEEE 1394 is also effective serial interface standard, with powerful functions and stable performances, and can support hot swap and plug and play. IEEE 1394 may connect as many as 63 devices in one port, with the tree or daisy chain topology structure between device.

　　IEEE 1394 Standard has defined two kinds of bus modes, i.e., Backplane mode and Cable mode. Among this, Backplane mode supports the transmission rate of 12.5. 25. 50Mbps; while Cable mode supports the transmission rate of 100. 200. 400Mbps. At present, the latest IEEE 1394b Standard can achieve the transmission rate of 800Mbps. IEEE1394 is a kind of universal interface for the platforms of PCs and home appliances, applicable for most products demanding for hi-speed data transmission, such as hi-speed external hard disk, CD-ROM, DVD-ROM, scanner, printer, digital camera and video cameras, etc. IEEE 1394 is divided into 6-needle Type-A interface with power supply function and 4-needle Type-B interface without power supply function. Type-A interface is compatible with Type B by the switcher, but Type-B transformed into Type-A is not able for power supply. 6-needle Type-A interface is widely used for Apple computers and periphery equipment, while most electric consumer goods and PCs use the simplified 4-needle Type-B interface and are equipped with the separate power adapter. IEEE1394 interface may directly be used as the on-line network card, or extended with more interfaces via the hub. Main boards containing no IEEE1394 interface will also obtain such function by plugging in IEEE 1394 extended cards.

PCMCIA
　　PCMCIA interface is also called PC card slot, also a standard facility for notebook PC like VGA output port. PC cars is made as per the industrial standard (PCMCIA Criterion), widely used in a lot of medium-sized digital equipment and industrial control equipment, but it’s mostly used in notebook PCs.

　　It may be said that, before the emergence of such plug and play ports as USB and IEEE1394, PC card slot is the only port actually supporting plug and play for notebook PCs. Further as PCMCIA Criterion has been widely supported, PC card products available in the market are numerous and have provided various choices of extension for notebook PCs.

　　PC card slot is equivalent to PCI slot of the desktop computer, the difference lies in that PC card slot is plug and play, PC card equipment is allowed to stop during the operation of operating systems. The extended card corresponding to PC card slot is called PC card, divided into three kinds according to their appearances, Type I/II/III, the length and width of them are all 85.6×54mm, the difference lies in their thickness, the thickness of Type I is 3.3mm, that of Type II is 5.0mm and that of Type III is 10.5mm, their interfaces are totally the same as 68 needles, so cards with three dimensions may be universally used if it’s allowed by the thickness of PC card slots.

　　The difference in thickness is due to the different requirements for internal equipment. For example, memory may be put into the thinnest card of Type I, but the micro hard disk can only be held at least in the thickness of card of Type II or Type III. All notebook PCs use the slots of Type II, two superposed slots of Type II may hold card of Type III, most mainstream CD-floppy disk exchangeable type of computers and all built-in device have two slots of Type II, most super-light and super-thin computer only has one slot of Type II.

PCI interface
　　The full English name of PCI is Peripheral Component Interconnect, namely 外部设备互联总线, it’s a kind of PC local bus standard launched in 1993. The major characteristics of PCI bus is the high transmission speed, and at present, it can realize the operating frequency of 66M, and may achieve the transmission rate of 533MB/s at the burst when the bus width is 64 and can satisfy the demands for external device with large throughput. Now almost all desktop computers have been configured with PCI interface on the main boards inside the hosts, just open the crates upon installation.

　VGA input: VGA interface applies 15-pin connection distributed asymmetrically, the operating principium of it is to modulate the image signals (frames) saved in the display memory in the form of figures into analog hi-frequency signals via RAMDAC, and then output them into the projectors for imaging. In this way, VGA signals will be put in the input end (inside the projects), not like other video signals that shall be converted by the matrix decoding circuit. It is known from the foregoing video imaging principium that the video transmission process of VGA is the shortest, so VGA interface possesses a lot of strong points, such as free of crosstalk, circuit synthesis, separation and loss, etc.

　　DVI input: DVI interface is mainly used for connecting to the computer video adapters with the function of digital display output to display RGB signals of computers. DVI (Digital Visual Interface) digital display interface is a kind of digital display interface standard enacted in September 1998 by the Digital Display Working Group (hereinafter shortly referred to as DDWG), which was incorporated on Intel Developer Forum.
　　DVI digital terminal can offer better signals than the standard VGA terminals. Digital interface has ensured all contents to transmit in digital format, ensured the data completeness in the transmission course from the hosts to the monitors, free from any undesired signal, and may get much clearer images.

　　Standard video input (RCA): it’s also called AV interface, generally is the white audio interface and yellow interface in couples and adopts RCA (with the vulgo of split head) for connection. For use, just connect the standard AV Cable of split head with the corresponding interface. AV interface can achieve the isolated audio and video transmission and avoid the degraded quality caused by the audio and video combinatorial jamming. However, as AV interface transmission is still a kind of video signals with mixed brightness and chromaticity (Y/C), so the display device is needed for the separation of brightness and chromaticity and chromaticity decoding for imaging. This process of first mixing and then separating will necessarily result in the losses in color signals, and there is great chance for the chromaticity signals and brightness signals to interfere that will impact the image quality finally outputted. AV has the vigor to some extent, however, its unconquerable defect of Y/C mix makes it impossible to use in some situations with visual limitation.

　　S video input: S-Video is called Separate Video in English. For better video effect, the people start to search for a kind of faster and clearer video transmission means, namely S-Video like the rising sun (also called two-component video interface). The role of Separate Video is to transmit video signals separately, i.e., it will separate the chromaticity signals C and brightness signals Y on the basis of AV interface and then transmit them in different channels. It was emerged and developed in the later of 1990’s and generally applies the standard 4 cores (excluding acoustics) or extended 7 cores (including acoustics). The video adapter and video equipment equipped with S-Video interface have been popular at present, such as the analog video acquisition/ TV sets with editing cards, TV sets with monitors at professional level, TV boxes and video projectors, etc.). Compared to AV interface, it stops conducting Y/C mixed transmission, so it will conduct no work of separating and decoding brightness and chromaticity and use the respective independent transmission channels, which has greatly avoided the image error inside video equipment caused by the signal crosstalk, and thus greatly improved the definition of images. Nevertheless, S-Video still mixes the chromatic aberration signals (Cr and Cb) in two channels into the chromaticity signals C in the same channel for transmission and then decodes them within the display device into Cb and Cr for processing. It will necessarily loss some signals somewhat, which will produce distortion, little but still discovered by testing in the rigorous video device at the broadcasting level. In addition, due to the limitation to bandwidth of chromaticity signals caused by the mixture of Cr and Cb, S -Video is very outstanding, but not perfect. Although S-Video is not the best, yet it’s applied as the most common video interfaces for other factors such as the current market status and comprehensive costs, etc.

　　Video chromatic aberration input: Now we can see the interface identifiers of YUV YCb Cr Y/B-Y/B-Y, etc. in some video workstation at professional level / video equipment or high-class movie player with editing cards at professional level. Although the marking methods and appearances of connectors are different on them, yet they refer to the same kind of interface chromatic aberration port (also called component video interface). Generally it adopts two identifiers of YPbPr and YCbCr, the former indicates the chromatic aberration output with progressive scan, while the latter indicates chromatic aberration output with interlaced scanning. It is shown by the above-mentioned relationship that as long as we know about the ＆#118alues of Y Cr Cb, we can get the ＆#118alue of G, i.e., it’s not necessary to use the fourth equation, so the procedure of video output and color processing has uniformly neglected the green chromatic aberration Cg and only reserve Y Cr Cb, this is the basic definition for chromatic aberration output. As the advanced products of S-Video, chromatic aberration output decompounds chromaticity signals C transmitted by S-Video into chromatic aberration Cr and Cb, it can avoid the mixed decoding of chromatic aberration in two channels and re-separate them and keep the maximum bandwidth of the chromaticity channel. The signals will pass through the inverse matrix decoding circuit to revive into RGB three-color signals for imaging. In this way, it has reduced the video signal channel between video source and display imaging to the maximum and avoided the image errors incurred from the cockamamie transmission courses. Therefore, the interface mode of chromatic aberration output is the best one among various interfaces of video output interface.

　　BNC port input: It’s generally used for connectors between the workstations and the coaxial cable, standard dedicated video equipment input, output port and BNC cable have five connectors used for receiving the red, green and blue horizontally synchronous and vertically synchronous signals. BNC connectors are different from the special display interfaces of ordinary 15-needle D-SUB standard connectors, it’s consisted of five independent signal connectors including red, green and blue three-color signals, line synchronous and field synchronous signal connectors, mainly used to connect the systems with higher request for scanning frequency such as workstation, etc. BNC connector may isolate video input signals and reduce the interference between signals, with larger signal bandwidth than that of ordinary D-SUB, for the best signal response effect.

　　The full name of RS232C Serial port: RS-232C Standard (Agreement) is EIA-RS-232C Standard, among it, EIA refers to Electronic Industry Association of America, RS refers to the recommended standard, 232 refers to the identification number, and C refers to the latest revision of RS232 (1969). Prior to this version, there are RS232B and RS232A versions. It stipulates the connecting cable, mechanical and electric characteristics, signal functions and transmission courses. The physical standards in common use include EIA� RS-232-C, EIA� RS-422-A, EIA� RS-423A, EIA� RS-485. This article only introduces EIA� RS-232-C (hereinafter referred to as 232 and RS232). Computer input and output interfaces are the most common serial interfaces; the standard interfaces in compliance with RS-232C Standard have 25 lines, including 4 data lines, 11 control lines, 3 time lines and 7 spare and undefined lines. 9 of them are commonly used, generally together with 25-pin D-sub ports, with the maximum transmission rate of 20kbps. The maximum length of cable is 15 meters. RS232C ports are used for inputting the computer signals to control the projectors.