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810-073479-215 处理器和存储器
网卡上面装有处理器和存储器（包括RAM和ROM）。网卡和局域网之间的通信是通过电缆或双绞线以串行传输方式进行的，而网卡和计算机之间的通信则是通过计算机主板上的I/O总线以并行传输方式进行。因此，网卡的一个重要功能就是要进行串行/并行转换。由于网络上的数据率和计算机总线上的数据率并不相同，因此在网卡中装有对数据进行缓存的存储芯片。
在安装网卡时将管理网卡的设备驱动程序安装在计算机的操作系统中，这个驱动程序以后就会告诉网卡，应当从存储器的什么位置上将局域网传送过来的数据块存储下来。网卡还要能够实现以太网协议。
网卡并不是立的自治单元，因为网卡本身不带电源而是使用所插入的计算机的电源，并受该计算机的控制，因此网卡可看成为一个半自治的单元。当网卡收到一个有差错的帧时，它就将这个帧丢弃而不必通知它所插入的计算机。当网卡收到一个正确的帧时，它就使用中断来通知该计算机并交付给协议栈中的网络层。当计算机要发送一个IP数据报时，它就由协议栈向下交给网卡组装成帧后发送到局域网。
随着集成度的不断提高，网卡上的芯片的个数不断的减少，虽然现在各厂家生产的网卡种类繁多，但其功能大同小异。网卡的主要功能有以下三个：
1. 数据的封装与解封：发送时将上一层交下来的数据加上首部和尾部，成为以太网的帧。接收时将以太网的帧剥去首部和尾部，然后送交上一层；
2. 链路管理：主要是CSMA/CD协议的实现；
3. 编码与译码：即曼彻斯特编码与译码。
810-073479-215 处理器和存储器
A network card contains a processor and memory (including RAM and ROM). The communication between the network card and the LAN is carried out by serial transmission through the cable or twisted pair, while the communication between the network card and the computer is carried out by parallel transmission through the I/O bus on the computer motherboard. Therefore, an important function of network cards is to perform serial/parallel conversion. Since the data rate on the network and the data rate on the computer bus are not the same, a memory chip is installed in the network card to cache the data.
When installing the network card, install the device driver that manages the network card in the computer’s operating system. This driver will later tell the network card where to store the data block transferred from the LAN from the memory. The network card must also be able to implement the Ethernet protocol.
The network card is not an autonomous unit, because the network card itself does not have a power supply but uses the power supply of the inserted computer and is controlled by the computer, so the network card can be seen as a semi-autonomous unit. When the network card receives an errant frame, it discards the frame without notifying the computer it is plugged into. When the network card receives a correct frame, it uses an interrupt to notify the computer and deliver it to the network layer in the protocol stack. When the computer wants to send an IP datagram, it is sent from the protocol stack down to the network card to assemble into frames and then sent to the LAN.
With the continuous improvement of integration, the number of chips on the network card continues to decrease, although there is a wide variety of network cards produced by various manufacturers, but its function is much the same. The main functions of network cards are as follows:
1. Data encapsulation and decapsulation: When sending, the data handed down by the previous layer is added to the header and tail to become the Ethernet frame. When receiving Ethernet frames, the header and tail are stripped, and then sent to the upper layer;
2. Link management: mainly the implementation of CSMA/CD protocol;
3. Coding and decoding: namely Manchester coding and decoding.
When installing the network card, install the device driver that manages the network card in the computer’s operating system. This driver will later tell the network card where to store the data block transferred from the LAN from the memory. The network card must also be able to implement the Ethernet protocol.
The network card is not an autonomous unit, because the network card itself does not have a power supply but uses the power supply of the inserted computer and is controlled by the computer, so the network card can be seen as a semi-autonomous unit. When the network card receives an errant frame, it discards the frame without notifying the computer it is plugged into. When the network card receives a correct frame, it uses an interrupt to notify the computer and deliver it to the network layer in the protocol stack. When the computer wants to send an IP datagram, it is sent from the protocol stack down to the network card to assemble into frames and then sent to the LAN.
With the continuous improvement of integration, the number of chips on the network card continues to decrease, although there is a wide variety of network cards produced by various manufacturers, but its function is much the same. The main functions of network cards are as follows:
1. Data encapsulation and decapsulation: When sending, the data handed down by the previous layer is added to the header and tail to become the Ethernet frame. When receiving Ethernet frames, the header and tail are stripped, and then sent to the upper layer;
2. Link management: mainly the implementation of CSMA/CD protocol;
3. Coding and decoding: namely Manchester coding and decoding.
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