I. USB2.0 specification
USB is the abbreviation of English universal serial bus, which means "universal serial bus" in Chinese. It is an interface technology applied in PC field, which is jointly developed by Intel, NEC, Compaq, DEC, IBM, Microsoft and Nortel. However, USB is not a bus standard, but an input/output interface standard for connecting computer systems and peripheral devices. USB connects all peripherals through a daisy-chain 4-pin standard plug. Theoretically, USB can connect 127 devices. The hardware part of USB system generally consists of three parts: USB host controller/root hub, USB hub and USB device.
Tips: Each USB device is addressed with 7-bit data, and the 7th power of 2 is 128, minus 00 addresses occupied by the host, which supports 127 devices at most. Of course, 127 is only a theoretical value, which may not be achieved in practice. At present, only11peripherals can be connected.
At present, there are mainly V 1. 1 and V2.0 in USB specifications. Compared with them, USB2.0 not only has1.1.5Mbps and 12Mbps specified in USB1 It also adds a high-speed data transmission mode of 480Mbps (note: the transmission rate of the second version of USB2.0 will reach 800Mbps, which is much higher than that of USB2.0, but its working principle and mode are exactly the same as USB 1. 1. The key technology to improve the transmission speed to 480 Mbps is to improve the unit transmission rate: the unit data transmission time of USB 1 is 1 millisecond, while that of USB2.0 is 1 millisecond.
At the same time, USB2.0 adopts backward compatibility design. The Enhanced Host Controller Interface (EHCI) in USB2.0 defines an architecture compatible with USB 1. 1, which adopts a set of extension technologies of communication protocols and develops a brand-new hardware component for the connection port: transmission converter. The buffer memory of the transmission translator can be accessed by full-speed and low-speed transmission devices and directly connected to the connection port for transmission. In this way, USB 1. 1 devices can be driven by USB2.0 to achieve backward compatibility. However, unlike USB 1. 1 HUB, USB2.0 HUB can directly use the transmission rate of 12Mbps for data transmission. There is a process of identification and conversion: USB2.0 HUB first distinguishes whether the inserted USB device is USB 1. 1 or USB2.0. If USB 1. 1 device is used, then the 480Mbps of USB2.0 should be converted into USB1./kloc-.
Tip: The maximum transmission rate of USB2.0 is 480Mbps, which is 60 MB/s, but it should be noted that this is the theoretical transmission value. If several devices * * * use a USB channel, the main control chip will allocate and control the available bandwidth of each device. For example, in USB 1. 1, all devices can only * * enjoy the bandwidth of1.5mb/s. If a single device occupies all the bandwidth of the USB interface, it will bring difficulties to other devices. This is a bit similar to the situation that * * * likes surfing the Internet.
Second, the IEEE 1394 specification
1987, Apple introduced a high-speed serial bus based on SISI interface-FireWire, hoping to replace the parallel SCSI bus. Later, the IEEE Union formulated the IEEE 1394 standard (Sony called it i.Link).
IEEE 1394 adopts daisy chain configuration, and tree structure configuration is also allowed, but various linear branches of the tree structure are still composed of linearly connected daisy chains. The IEEE 1394 bus also needs a master adapter to connect to the system bus. Usually, we refer to the main adapter and its ports as the main ports. The main port is the root node of the tree configuration structure of IEEE 1394 bus. A master port can connect up to 63 devices, which are called nodes, and they can form a parent-child relationship (pictured). The longest cable between two adjacent nodes is 4.5m However, when two nodes communicate, they can be re-driven by the transfer of more than 15 nodes at most, so the maximum communication distance is 72m, and the cable does not need a terminator.
Different from USB, all the resources of IEEE 1394 standard interface structure are identified in the form of unified storage addressing, which realizes resource configuration and management. So in this sense, IEEE 1394 can be regarded as the bus architecture equivalent to PCI bus. In addition, compared with USB, IEEE 1394 supports synchronous and asynchronous transmission. Asynchronous transmission is a traditional transmission mode. When transmitting data between the host and peripherals, it is not real-time data transmission to the host, but emphasizes batch data transmission, but the accuracy of data is very high, which is its main feature. Synchronous transmission emphasizes the real-time performance of its data. With this function, data can be directly transmitted to the computer through the high bandwidth and synchronous transmission of IEEE 1394, which saves the expensive buffer equipment in the past. This is one of the reasons why digital cameras always use IEEE 1394 as the standard interface.
At present, there are only two specifications: IEEE 1394. One is IEEE 1394a, which is the current mainstream specification and mainly supports two modes-backplane mode and cable mode. Backplane mode only supports the transmission rate of 12.5Mbps, 25.5Mbps or 50Mbps, while cable mode provides the required 100Mbps, 200Mbps and 400Mbps. However, the transmission speed of IEEE 1394 follows the principle of low speed: because data can be exchanged at different rates in the same network, if a 200Mbps device is added between two devices with a transmission speed of 400Mbps, the data transmission speed will be subject to 200Mbps. The other is IEEE 1394b, which is the standard of the next generation PC. Will be directly expanded from 400Mbps of IEEE 1394a to 800Mbps and 1600Mbps. If optical fiber is used, the maximum transmission rate will be increased to 3.2Gbps. In addition, compared with IEEE 1394a, IEEE 1394b uses the connection distance of 100 m (note: this will be reduced to 100MB/s at the expense of reducing the transmission rate), and In addition, the IEEE consortium introduced a new physical layer configuration called "Betamode" in the IEEE 1394b specification to improve the management capability of the IEEE 1394b system.
Third, who wins and who loses.
1. cost level
In terms of cost, USB2.0 has more advantages. Because the USB host controller is built into the current motherboard chipset, and most peripherals are equipped with USB interfaces as standard. Therefore, users can enjoy the convenience brought by USB without any other fees. For IEEE 1394, the structure of IEEE 1394 controller is complex, and it is difficult to integrate into the motherboard chipset in terms of technology and cost, so there are few chipsets integrating IEEE 1394 controller in the market at present. In order to realize the function of IEEE 1394, we can only plug in the expansion card of IEEE 1394, but the motherboard is provided in the form of integrated additional chips, which directly leads to the increase of use cost.
2. Ease of use
In terms of ease of use, IEEE 1394 is dominant. Although both specifications support hot plug function, USB2.0 needs Windows XP SP 1 for operating system support (Note: Although Windows2000/XP supports USB, at this time, it only supports USB 1. 1 standard, so the transmission rate of USB2.0 is greatly reduced, and operating systems below Windows2000 need to be driven. Since Windows 98, it has provided comprehensive support for IEEE 1394. The installation of IEEE 1394 can be used without any driver, which is completely inferior to USB2.0, and IEEE 1394 supports point-to-point function. If two computers are connected together, we can use them directly, without IP or any settings. In addition, although USB2.0 only provides a DC voltage of 5V and a current of 0.5A, it is enough for ordinary devices, but if it is a device with large power consumption, such as an external burner, MO driver, printer, etc., it must be connected to an external power supply to use it. However, IEEE 1394 provides a voltage of 8V ~ 40V and a current of 5A. Theoretically, it can provide the maximum power of 200W(40V×5A), which is much higher than that of USB2.0 (if you want to achieve such a high power, you need a more powerful power supply, but only a lot of IEEE 1394 devices are connected in series will you use such a high power). Who will use so many IEEE 1394 devices at once? )。
3. Transmission speed
Although USB2.0 can provide 480Mbps, which is slightly higher than the 400Mbps provided by IEEE 1394a, does it mean that USB2.0 has more advantages? The answer is no, in general, the actual transmission speed of USB2.0 is only 2 ~ 13 times that of USB 1, which is far from its theoretical value. Moreover, if several devices use a USB channel, the main control chip will allocate and control the bandwidth that each device can control, and the transmission speed will be lower. However, this situation rarely occurs in the mainstream IEEE 1394a. According to the related comparison test (see table), IEEE 1394a is far superior to USB2.0 in burst transmission rate, average read/write rate, workstation performance and file replication rate. As you can imagine, the advantages of IEEE 1394b will be more obvious. However, IEEE 1394 has a disadvantage that the IEEE 1394 bus needs to occupy a lot of resources, so it needs a high-speed CPU to achieve the best transmission rate.
It can be said that IEEE 1394 has advantages over USB2.0 in performance and application. However, because the first position of IEEE 1394 is in multimedia applications, which is different from the popularization route of USB, the equipment of IEEE 1394 will be much more expensive than USB equipment, and the high patent fee of IEEE 1394 will lead to high use cost. This is the biggest weakness of IEEE 1394. However, with the integration of IEEE 1394 controller in the future chipset, I believe this problem will be alleviated. In addition, it is worth noting that IEEE 1394 adopts the design mode of non-master-slave architecture, and peripheral devices can transmit data point-to-point without a computer, which is incomparable to USB2.0, and this is also the main space of IEEE 1394.
Therefore, IEEE 1394 and USB2.0 will still merge in the future.
I suggest you go to the next USB driver.