NIC - Network Interface Card


Background.  A NIC - Network Interface Card is almost necessary for directly connecting computers and other devices to networks.  You don't necessarily need them in all situations, for example, when you use a dial up connection a modem displaces the need for a NIC.  The NIC translates the parallel signal produced by the computer into a serial format to be sent over a network.  The 0s and 1s of binary communication are translated into electrical impulses, light pulses, radio waves or whatever signal medium is being used.

When selecting a NIC it is important to consider the following issues.

  • Network Architecture
    • it needs to be able to work with the existing transmission technology
      • this might be attained through use of a media filter
  •  Media Type
    • what is the type and size of cabling?
      • coax
      • UTP
      • STP
      • fiber optic
    • wireless
      • radio
      • infrared
      • etceteras
  • Data Transfer Speed
  • Available Bus Type
    • ISA - Industry Standard Architecture
      • 16 bit expansion slot on the motherboard
    • EISA - Extended ISA
      • 32 bit architecture compatible with ISA
      • most modern ISA slots are actually EISA
    • PCI - Peripheral Component Interconnect
      • 32 bit bus
        • used for computers after Pentiums and Macintosh
      • supports Plug and Play
    • MCA - Micro Channel Architecture
      • IBM proprietary
      • 16 or 32 bit
    • PCMCIA - Personal Computer Memory Card International Association
      • an input/output bus that is close to the size of credit cards
      • usually used on laptops and notebooks
    • special
      • SCSI bus
      • USB cards
  • Operating System

Use and Configuration.  Configuring NICs is actually pretty similar to configuring a modem.  You might need to set some or all of the following.

  • IRQ
  • I/O Address
  • Memory Address

You might need to configure other parameters if the NIC is a combo card which can be used with different media types.

Most NICs make use of either IRQ 3 or IRQ 5 and will come with a default set.

IRQ stands for "Interrupt Request." PCs use interrupt requests to manage various hardware operations. Devices such as sound cards, modems, and keyboards can all send interrupt requests to the processor. For example, when the modem needs to run a process, it sends an interrupt request to the CPU saying, "Hey, hold up, let me do my thing!" The CPU then interrupts its current job to let the modem run its process.

It is important to assign different IRQ addresses to different hardware devices is because the interrupt request signals run along single IRQ lines to a controller. This interrupt controller assigns priorities to incoming IRQs and sends them to the CPU. It's kind of like taking a number at the local deli, except the hardware usually only has to wait a couple of nanoseconds instead of like twenty minutes). Since the interrupt controller can control only one device per IRQ line, if you assign the same IRQ address to multiple devices, you are likely to get an IRQ conflict. This can cause a range of errors from not allowing network connections to crashing your computer. So make sure you assign unique IRQs to new hardware you install and avoid the frustration and keyboard throwing that conflicts can cause.

The following table lists the standard devices or processes associated with each IRQ.  Many of these devices are not going to be on all computers and then their IRQ can be used for other things.


Device Default IRQ
VGA Graphics Adapter 2 (9)
COM 2 and COM 4 (secondary serial port) 3
COM 1 and COM 3 (primary serial port) 4
Secondary parallel port (LPT2) or sound card 5
Floppy disk controller 6
Primary parallel port (LPT1) 7
Real time clock 8
Primary SCSI controller 10
Secondary SCSI controller 11
PS/2 Mouse 12
Math coprocessor 13
Primary IDE controller 14
Secondary IDE controller 15


Hopefully you remember the earlier definition, but anyway, the I/O Port is a channel through which data is transferred between the hardware device and the processor.  These port numbers are designated using hexadecimal numbers.  The ports that are usually available for the NIC are
  • 300 to 30F
  • 310 to 31F

To also reiterate from an earlier page, a memory address is a location in RAM used for the storage of pertinent incoming and outgoing data.  These are usually set by default by the manufactrurer.  Some NICs do not make use of the computer's memory for this and so don't need an assigned memory address.