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The interface in the computer is the "main artery" for data transmission between the host and the external device. As the processor speed increases, the data transmission speed of the interface also needs to be gradually increased, otherwise it will become a bottleneck in the development of the computer.

Parallel data transmission technology has always been an important means to increase the data transmission rate, but further development has encountered obstacles. First of all, because the premise of the parallel transmission method is to use the same timing to propagate the signal and use the same timing to receive the signal, and excessively increasing the clock frequency will make it difficult to keep the timing of data transmission in sync with the clock. The wiring length is slightly different, and the data will be different from the clock. In addition, increasing the clock frequency can easily cause mutual interference between signal lines, resulting in transmission errors. Therefore, it is difficult to achieve high speed in the parallel method. From the perspective of manufacturing cost, increasing the bit width will undoubtedly lead to an increase in the number of wiring on the motherboard and expansion board, and the cost will rise accordingly.

In terms of external interfaces, the IEEE 1284 parallel port has a rate of up to 300kBps, and the use of compression technology to transmit graphics data can increase to 2MBps, while the data transfer rate of the RS-232C standard serial port is usually only 20kbps, and the data transfer rate of the parallel port is undoubtedly To win. Therefore, the parallel port has always been the preferred connection method for printers. For a dot matrix printer that only transmits text, the transmission speed of the IEEE 1284 parallel port can be said to be more than enough. However, for laser printers that have been speeding up repeatedly, the situation has changed. When the author uses Epson 6200L to print 2MB pictures, the speed difference is not obvious, but when printing a 7.5MB picture file, it took 18 seconds from clicking "Print" to the final paper output using the USB interface, while using the parallel port , It took 33 seconds. This test result shows that the current parallel port is already incompetent for popular laser printers.

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