The earliest Centronics parallel cable has a length of 2 meters and can only support 10KB/s data rate transmission, which does not require high performance. In order to increase the data rate to more than 2MB/s, many special requirements are imposed on the IEEE1284 cable:
1) Because it is parallel data, in order to avoid crosstalk between BIT data during transmission, each data line needs to match a ground line to form a twisted pair structure;
2) The unbalanced characteristic impedance between each pair of signals and return ground is 62 ohm ± 6 ohms (on the frequency band 4M-16MHz);
3) Inter-line crosstalk does not exceed 10%;
4) The cable has a shield and is connected to the connector's shield, using a 360-degree package.
The interface in the computer is the "big artery" that transfers data between the host and the external device. As the speed of the processor rises, the data transmission speed of the interface needs to be gradually increased. Otherwise, it will become a bottleneck for computer development.
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 signals and receive signals at the same timing, it will be difficult to excessively increase the clock frequency to make the timing of the data transmission and the timing of the clock coincide. The wiring length is slightly different and the data will be different from the clock. The timing of delivery, in addition, increase the clock frequency is also easy to cause interference between the signal lines, resulting in transmission errors. Therefore, it is difficult to achieve high speed in the parallel method. From the point of view of manufacturing costs, 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 increase accordingly.
Technological advances are endless and endless, and no technology can ever be applied. After the computer technology enters the THz era in the future, the requirement for signal transmission speed will be even higher. Whether the differential transmission technology used in the new serial interfaces such as USB and FireWire can meet future requirements, does it need another better technology? Another breakthrough in the frequency of completion, these require the common concern of people.