Serial port is called serial interface, now the computer generally have two serial port: COM1 and, COM2. you can see the back of the computer 9-pin D-shaped interface is, sometimes we also call it RS-232 interface. Now there are a lot of cell phone data lines or logistics receivers are using COM port to connect to the computer.
Universal Serial Bus (Universal Serial Bus) referred to as USB, is the current computer on the more widely used interface specification, the USB interface is a computer motherboard on a four-pin interface, in which the middle two pins to transmit data, two pins on both sides of the power supply to the peripheral. USB interface is fast, easy to connect, does not require external power supply, and at the same time, external devices have good compatibility, up to 127 can be connected to the computer. USB has two specifications, USB 1.1 and USB 2.0.
The USB interface can be connected to speakers, modems, digital cameras, monitors, joysticks, scanners, mice, keyboards, and other peripheral devices, which makes it possible to hot-swap, i.e., plug in and out of USB devices without shutting down the computer.
Interface type:
The RJ-45 interface is the most commonly used interface for Ethernet, and RJ45 is a common name for a modular jack or plug standardized by IEC (60)603-7 that uses eight positions (8 pins) defined by an international connector standard.
The RS-232 interface (also known as EIA RS-232-C) is one of the most commonly used serial communications interfaces today. It was developed in 1970 by the Electronic Industries Association of America (EIA) in conjunction with the Bell System, modem manufacturers and computer terminal manufacturers **** with the development of standards for serial communications. Its full name is "data terminal equipment (DTE) and data communications equipment (DCE) between the serial binary data exchange interface technology standard" the standard provides for the use of a 25-pin DB25 connector, the connector's signal content of each pin to be specified, but also on the various signal levels to be specified.
Parallel port (LPT port)
Parallel port (Parallel Port/Interface) is a 25-pin interface used in the early days of computers, commonly known as the print port. The parallel port uses a 25-pin, double-row socket, and in addition to its most common application in printers, it can also be used to connect devices such as scanners, ZIP drives, and even external network cards, tape drives, and certain expansion drives.
USB (Universal Serial Bus) Universal Serial Bus is a new peripheral interface standard initiated by Intel, Microsoft, Compaq, IBM, NEC, Northern Telcom, and several other major vendors. USB transmission speeds of 12Mbps, the latest USB2.0 up to 480Mbps; cable maximum length of 5 meters, USB cable has 4 lines, 2 signal lines, 2 power lines, can provide 5 volts of power, USB cable is also divided into shielded and unshielded two kinds of shielded cable transmission speed of up to 12Mbps, the price is more expensive, the unshielded cable speed of 1.5Mbps, but the price is cheaper; USB through the serial connection can be connected to a maximum of 127 devices in series; Supports plug-and-play and hot-swap.
The difference between a serial port and a parallel port:
The serial port is described as a single lane, while the parallel port has eight lanes capable of transmitting eight bits (one byte) of data at the same time.
But the parallel port is not fast, due to the interference between the 8-bit channels. Transmission by the speed is limited. And when there is a transmission error, you have to retransmit 8 bits of data at the same time. Serial port has no interference, just retransmit one bit after transmission error. So it is faster than parallel port. This is how serial hard disk is valued.
PCI
The Peripheral Component Interconnect (PCI), developed by Intel, is a local bus standard. The bus is a channel used to transfer data to and from (input/output) the computer and peripherals. Most computers typically use a 32-bit PCI bus, which operates at 33MHz and has a throughput rate of up to 133MBps
PCI stands for Peripheral Component Interconnect, and is the most widely used interface in personal computers today, with almost all motherboards featuring such slots. PCI slots are also the most numerous slot type available on a motherboard. On popular desktop motherboards, ATX motherboards typically have 5 to 6 PCI slots, while smaller MATX motherboards have 2 to 3 PCI slots, making them ideal for a wide range of applications.
PCI is a localized bus introduced by Intel in 1991. From a structural point of view, PCI is a first-level bus inserted between the CPU and the original system bus, specifically by a bridge circuit to achieve the management of this layer, and to realize the interface between the upper and lower to coordinate the transfer of data. The manager provides signal buffering so that it can support 10 peripherals and maintain high performance at high clock frequencies. It provides connection interfaces for graphics cards, sound cards, network cards, MODEMs, and other devices, and it operates at 33MHz/66MHz.
The earliest proposed PCI bus operated under the 33MHz frequency, with a transmission bandwidth of 133MB/s ( With the demand for higher performance, a 64-bit PCI bus was proposed in 1993, and later it was proposed to increase the frequency of the PCI bus to 66MHz. Currently, the 32-bit, 33MHz PCI bus is widely used, and the 64-bit PCI slot is more commonly used in server products.
With a bandwidth of only 133MB/s, the PCI bus is more than adequate for most input/output devices, such as sound cards, network cards, and video cards, but it is unable to meet the demands of increasingly powerful graphics cards. PCI Express Gen.3 is a video interface standard designed for carrying uncompressed digital video data and to maximize the visual quality of digital display devices, such as LCD monitors, digital projectors, digital projectors, and so on.
The parallel port (also known as IEEE 1284, Centronics), currently used primarily as a printer port, is a 25-pin D-shape connector. The term "parallel" refers to the simultaneous transmission of 8-bit data over a parallel line, which greatly increases the speed of data transmission. However, the length of the parallel transmission line is limited, because the length increases, the interference will increase, and the data will be prone to errors. At present, computers are basically equipped with a parallel port. The parallel interface, also known simply as "parallel port", is an enhanced bidirectional parallel transmission interface. The advantages are no other card in the PC, unlimited number of connections (as long as you have enough ports), easy installation and use of the device, and a maximum transfer speed of 1.5 Mbps. Currently, parallel interfaces in computers are mainly used as printer ports, and the interfaces are no longer 36-pin connectors, but rather 25-pin D-shape connectors. The so-called "parallel", refers to the 8-bit data transmission through the parallel line at the same time, so that the data transmission speed is greatly increased, but the parallel transmission line length is limited, because the length increases, the interference will increase, prone to error.