The biggest difference between 1394 and USB is that 1394 transmission does not require CPU participation, and the two 1394 devices are peer-to-peer connections; The USB device is not peer-to-peer when transmitting data, and one of them is used as the main device, which requires the CPU to participate in order to work, and the CPU share will increase as the speed increases.
1394 is more like a traditional video device interface than USB: two 1394 devices can be contacted by hand directly through the 61883 protocol and transmit data. For example, two DVs or one DV and one DV recorder. After connecting through the 1394 port, one of the devices can play video and the other can directly record video. To achieve this through a USB interface, the receiver must have a powerful CPU to power the USB interface, although this is okay for connecting to the computer (we can use the computer's USB port as the main device interface, Driven by the CPU on the computer), but the DV machine is used as a video frequency device or household appliances, rather than as a computer accessory like a USB camera. Therefore, to realize that two DV devices can be connected to each other through the USB interface like ordinary household appliances and ordinary video equipment, it is necessary to integrate such a strong CPU in the DV or DV recorder, which will greatly increase the cost and power consumption of the machine. Therefore, from the current point of view, USB2.0 will not replace 1394 to become the standard interface on DV devices, at best as a supplement to 1394.
Although the previous post introduced a lot, let me talk about the difference between USB and 1394:
1, 1394 is a high-speed serial bus, and USB is the computer system and peripheral equipment to connect the input / output interface technology.
The 1394 has the characteristics of supporting synchronous and asynchronous transmission. With its high-bandwidth nature, the 1394 interface utilizes the method of synchronous transmission to transmit data from peripheral devices directly to the computer. And USB does use asynchronous transfer method, need to use buffer memory for data access.
3, from WIN98, 1394 has been fully supported. You can use it without installing any driver 1394. And USB2.0 needs WINDOWS XP + SP1 to provide support, WIN2K / WINXP only supports USB1.1 standard, win98 / ME must also install driver, so that USB2.0 transmission rate is difficult to play.
4, although the transmission rate of 1394A is 400Mbps and the transmission rate of USB2.0 is 480Mbps, but usually the actual transmission rate of USB2.0 is 24-156Mbps, far less than its theoretical value. If there are other USB devices in a computer (such as USB mouse, keyboard, etc.), the control chip in the motherboard redistributes bandwidth to each device, and the transmission rate is lower. But this is rarely the case with the 1394, which can access data at a steady and high speed.
5, the disadvantage of USB is that it takes up a lot of system resources, and it needs to meet the best transmission rate with high-speed CPU, and 1394 is not.
The USB1.1 theoretical speed is 12 Mb / s, while the DV format is usually 25 Mb / s, Then USB 1.1 cannot reach this speed in theory, and even less so in practice. To this end, using USB transmission can only reduce the image, which was originally 720x576 to 320x240, and the frame rate is reduced, so the image quality is not good, but of course it can still be seen. This doesn't have much to do with the configuration of the machine. If you switch to USB2.0 in the future, of course, it will change, but it is not necessary.
