Network adapter is also known as network card or network interface card (NIC), English name NetworkInterfaceCard. it is a device to make computer networking. What is usually referred to as a NIC is a network adapter that connects a PC to a LAN. Network Interface Card (NIC) is inserted in the motherboard slot of the computer, responsible for converting the data to be transmitted by the user into a format that can be recognized by other devices on the network, and transmitted through the network medium. Its main technical parameters for the bandwidth, bus mode, electrical interface mode. Its basic functions are: data conversion from parallel to serial, package assembly and disassembly, network access control, data caching and network signaling. Currently the main 8-bit and 16-bit NICs. NICs must have two major technologies: a NIC driver and I/O technology. The driver makes the NIC and the network operating system compatible, realizing the communication between the PC and the network.I/O technology can realize the communication between the PC and the NIC through the data bus. The network card is the most basic element in a computer network. In a computer local area network, if there is a computer without a network card, then this computer will not be able to communicate with other computers, that is to say, this computer and the network is isolated. Different classifications of NICs: According to different network technologies, NICs are categorized differently, such as the well-known ATM NICs, Token Ring NICs and Ethernet NICs. According to the statistics, about 80% of the LANs adopt Ethernet technology at present. It is specially designed according to the working characteristics of different servers of the working object, which is more expensive but with good performance. In terms of compatible network cards, at present, network cards are generally divided into ordinary workstation network cards and server-specific network cards. Server-specific network card is designed to adapt to the network service types are more, there are differences in performance, can be categorized according to the following criteria: according to the different bandwidths supported by the card can be divided into 10M NIC, 100M NIC, 10/100M adaptive NIC, 1000M NIC several kinds of; according to the different types of buses of the card is divided into the ISA NIC, EISA NIC and PCI NIC three major types of cards, including ISA NICs and PCI NICs are more commonly used; the bandwidth of ISA bus NICs is generally 10M, and the bandwidth of PCI bus NICs ranges from 10M to 1000M. The same 10M NIC, because the ISA bus is 16-bit, while the PCI bus is 32-bit, so the PCI NIC is faster than the ISA NIC. Network card interface type: According to the different transmission media, the network card appears AUI interface (thick cable interface), BNC interface (thin cable interface) and RJ-45 interface (twisted-pair interface) three types of interfaces. So when choosing a network card, you should pay attention to the type of interface supported by the card, otherwise it may not be applicable to your network. The common 10M NICs on the market mainly have single-port NICs (RJ-45 interface or BNC interface) and dual-port NICs (RJ-45 and BNC two interfaces), with less AUI thick cable interface NICs. The 100M and 1000M NICs are generally single-port cards (RJ-45 interface). In addition to the interface of the card, we often have to pay attention to whether the card supports diskless boot. If necessary, we should also consider whether the card supports fiber optic connection. Purchase of network cards: According to statistics, the vast majority of LANs use Ethernet technology, thus focusing on Ethernet cards as an example, to talk about some of the issues that should be noted when purchasing a network card. Purchase should pay attention to the following key points: Application areas of network cards ---- At present, Ethernet network cards have 10M, 100M, 10M/100M and Gigabit network cards. For large data volume networks, servers should use Gigabit Ethernet NICs, which are mostly used for the connection between servers and switches to improve the overall system response rate. The 10M, 100M and 10M/100M NICs are among the most frequently purchased and commonly used network devices, and the price difference between these three products is not significant. The so-called 10M/100M adaptive means that the card can be automatically negotiated with the remote network device (hub or switch) to determine the current available rate is 10M or 100M. For the usual file **** enjoyment and other applications, the 10M card is already sufficient, but for the future may be voice and video applications, 100M card will be more conducive to the transmission of real-time applications. Given the foundation that 10M technology already has (e.g., previous hubs and switches, etc.), a common workaround is to purchase a 10M/100M NIC, which is good for both protecting the investment already made and for further expansion of the network. In terms of overall price and technological development, Gigabit Ethernet to desktop machines is still some time away, but the era of 10M is already fading away. Thus, for small and medium-sized enterprises, 10M/100M network card should be the first choice when purchasing. Pay attention to the bus interface mode ---- current desktop and notebook computers in the common bus interface mode can be found from the mainstream network card manufacturers to find applicable products. It is worth noting, however, that 100M NICs with ISA interfaces are hard to find on the market.Since 1994, the PCI bus architecture has increasingly become the bus of choice for NICs and is now firmly established in servers and high-end desktop machines. The upcoming shift is the extension of this NIC to all desktop machines. the high performance, ease of use, and enhanced reliability of PCI Ethernet NICs have led to their widespread adoption by standard Ethernet networks and support from the PC industry. NIC compatibility and utilized technologies ---- Fast Ethernet at the desktop level generally uses 100BaseTX technology with UTP as the transmission medium, therefore, Fast Ethernet NICs are equipped with an RJ45 interface. Since small office networks commonly use twisted-pair cable as the transmission medium for the network with structured cabling, it is sufficient to choose a network card with a single RJ45 interface. Applicability of good network card should be certified by the mainstream operating systems, at least with the following operating system drivers: Windows, Netware, Unix and OS/2. Smart card with its own processor or with a specially designed AISC chip, can assume the use of non-smart card by the computer processor to undertake some of the tasks, and therefore, even in the case of a large amount of information traffic in the network. Therefore, even when the network information traffic is very large, it also takes up very little computer memory and CPU time. Intelligent network card performance is good, the price is also higher, mainly used in servers. In addition, some network cards in the BootROM to do articles, adding anti-virus features; some network cards with the motherboard, with the help of certain software, the realization of WakeonLAN (Remote Wake-up) function, you can start the computer remotely through the network; there are also computers simply integrated into the motherboard network card. NIC manufacturers ---- due to the maturity of the NIC technology, the current production of Ethernet NIC manufacturers in addition to foreign companies such as 3Com, Intel and IBM, Taiwan's manufacturers to production capacity and more in the mainland set up factories and other advantages, its price is relatively cheap.