A network card (also called network adapter or NIC for English. Network Interface Card or Network Interface Controller ) is related to the information technology an electronic circuit for connecting a computer to a local network for the exchange of data .
This function used to be located almost exclusively on a plug-in card for an expansion slot and is now integrated directly on most motherboards . Colloquially, the term is also used for an integrated network interface that is not located on a separate plug-in card.
Their primary task is to establish a physical connection to the network using a suitable access method (e.g. CSMA / CD ) and to implement the first or second OSI layer (usually Ethernet ).
Network cards consist on the one hand of a network interface that is designed for the respective network types or the network architecture, and on the other hand of a bus interface that is adapted to the respective computer architecture . For some years now, practically all computers have already had the (wired) network functionality on their motherboard and only need one network card if a further, faster or wireless connection is required. For wireless networks, USB sticks or PCI Express Mini Cards are more common than traditional built-in cards.
In the early 1980s there were still many competing network architectures and network card types that were more widespread, in particular ARCNET , Ethernet , LocalTalk and Token Ring .
- ARCNET operated with a token passing procedure at 2.5 Mbit / s and mostly worked on coaxial cables (RG-62) as a bus or star topology . Until 1985 it had significant price advantages over Ethernet, resulting in high market shares. Thanks to the token-passing method, ARCNET works deterministically and can therefore be used in real-time systems, which is problematic with unswitched Ethernet , which is not suitable for maximum loads .
- At first, Ethernet mostly used 10 Mbit / s cards, which were usually connected as a bus via a coaxial cable (RG-58; thin or thick wire). Until 1985 these cards were still very expensive, with the NE1000 / NE2000 models there was a drop in prices. Ethernet is the most widely used method today. Many of the initial disadvantages, especially the problems with high loads, have been largely eliminated through improved technology and components such as switches.
- LocalTalk was used almost exclusively by Apple and used a 232 kbit / s token passing method over a two-wire bus cabling closely based on the serial RS-422 interfaces. This type of networking was very popular with Apple computers, because from 1984 to 1998 this interface was standard on every Apple computer (without an additional plug-in card). For PCs (including Novell Netware server) there was appropriate LocalTalk network cards, usually in 8- bit - ISA bus version.
- Token Ring was mainly used in the IBM environment (banks), it worked at 4 Mbit / s or 16 Mbit / s in the token-passing process and had a ring topology.
When the Fast Ethernet standard was passed in 1995 , the market thinned out and pure 10 Mbit / s Ethernet cards were replaced by 10/100 Mbit / s cards. These are no longer the most common, as Gigabit Ethernet cards (which are also 10/100 Mbit / s compatible) were able to gain significant market shares.
These cards are connected via twisted pair cables with RJ45 plugs to a hub or now mostly to a switch and thus form a local network ( LAN ).
With the 1000 Mbit / s network cards, which are usually connected via twisted pair cables with RJ45 plugs ( 1000BASE-T ), fiber optics (e.g. 1000BASE-SX ) for connecting end nodes began to spread. Optical fibers are used more and more frequently for faster connections and almost exclusively from 25 Gbit / s.
Network cards for wireless networks ( Wireless LAN ) were initially mainly used in mobile devices such as B. Notebooks or PDAs are used, but are increasingly being built into desktop PCs .
On the bus side, different standards alternated with network cards. There were not network cards for all bus systems, for example not for the Accelerated Graphics Port (AGP). There were also more exotic constructions using the SCSI bus or printer interfaces, the latter being used for a while in notebooks. In the UNIX area, with workstations and servers , as well as with mainframes , there were numerous manufacturer-specific bus systems that were also used for network cards. Here is an overview of typical bus systems for network cards:
- ISA : Around 1980, at the beginning, network cards with the widespread ISA bus interface dominated PCs, initially in 8- bit technology ( XT bus architecture ) (e.g. NE1000 ) and later in 16-bit design (e.g. B. NE2000 )
- PCMCIA or PC-Card: This interface was mainly used in notebooks, to put it simply, it is a miniaturized ISA interface.
- VESA Local Bus : Short-lived standard in the first half of the 1990s, developed for the faster connection of plug-in cards.
- NuBus : From 1980, aninterface widely usedby Apple Computer and NeXT Computer .
- MCA : A bus system propagated by IBM from 1987 as the successor to ISA. A failed attempt to introduce an incompatible and not open but improved bus.
- EISA : A bus system propagated by everyone except IBM as the successor to the ISA bus at the end of the 1980s. A compatible ISA bus extension for 32-bit transfer via an extended contact strip. EISA was mainly used for workstations and servers.
- PCI : Around 1990, the actual successor to the ISA bus architecture. As an open standard, it also replaced the EISA bus and was also used to replace various proprietary bus systems. For example, PCI replacedthe NUBUSat Apple Computer ,the GSC / HSC and the HP-PBat Hewlett-Packard , andthe MCAat IBM .
- USB is extremely widespread in both desktop computers and laptops and allows simple use via plug and play , particularly popular with WLAN .
- In 2004 PCI-Express replaced the PCI bus and the AGP popular for graphics cards.
- ExpressCard : Notebook interface based on PCI-Express x1
- Onboard: Since the early 2000s, almost all computer motherboards have built-in LAN interfaces, so dedicated plug-in cards are usually no longer necessary. Often the same electronic components are used, only the plug connections are missing, often the controller is also integrated in the chipset . These chips are treated like plug-in cards by the driver software (e.g. there is usually a PCI interface that is controlled / programmed).
10 Mbit / s XT Ethernet network card with RG58 socket and 15-pin. SUB-D socket ( AUI )
A common network card has only one Ethernet connection, special versions also have several (up to four). The price of an inexpensive standard network card has fallen from several 100 EUR (1990) to currently (2009) around 5–15 EUR. Higher quality network cards (with better data throughput, lower CPU load , better equipment) cost up to 100 EUR depending on the version, very special cards (e.g. with several independent connections) also cost more. Since the end of 2003 many new PCs have had Gigabit Ethernet connections on the motherboard.
Each Ethernet network card has a globally unique MAC address assigned by the manufacturer. However, there are also drivers that allow the MAC address to be temporarily changed using software, which can cause security problems in a LAN .
Boot from the network
Many network cards have a socket for a so-called boot - PROM (also called boot ROM). This memory module is displayed in the address area of the computer and allows the computer to be started from the network without a local (built into the computer or directly connected) mass storage device, such as. B. a hard drive. Different computer architectures (Apple, PC), operating systems and different network environments ( IPX / SPX , TCP / IP ) require different boot programs, so that it is up to the user to choose the network card with a PROM (or EPROM ) with the appropriate one To populate boot program. The classic way for PCs is a so-called Novell Boot PROM for use with Novell Netware and Novell's own network protocol. More modern concepts based on TCP / IP are e.g. B. Intel's PXE and the open source and free solutions Etherboot and Netboot.
All approaches have one thing in common: The program in the boot PROM is started and latches into the rest of the boot process. At some point, either before or after the search for a bootable local medium, the boot PROM is reactivated and an operating system reloads over the network. This usually happens in small steps, first a utility program with extended network functions, then larger parts of the operating system. Finally, control is passed to the operating system, which then usually makes use of other network services.
Instead of a socket, some network cards have a reprogrammable EEPROM that is integrated directly into the chipset of the network card , which can be loaded with an auxiliary program with various boot programs so that the computer does not have to be opened. Motherboards with integrated network adapters, as well as many UNIX - workstations , use a part of the already existing system EEPROMs ( BIOS ) as a boot PROM, also can usually use a utility to any boot program to be recorded or the manufacturer are determined BOOTP or PXE. For reasons of cost, manufacturers of cheap products in particular often do without the base for the boot PROM. Outside of the PC world, starting from the network is often part of the permanently installed start program, e.g. B. on many Sun machines and modern Macintosh systems. However, mostly only a special selection of network adapters certified by the manufacturer is supported.
All modern Apple computers can boot from a computer on which the server version of Mac OS X is running.