The bus interface is one of the most important considerations when acquiring a NIC card. The type of bus interface you may require is dependent on the local machine that will be employed for data communication over the network. The types of bus interfaces for an Ethernet NIC are ISA, EISA, PCI, Embedded and PCMCIA.

The ISA bus has been one of the most common Bus interfaces that have been used on PC's since their conception. The ISA bus provides either 8 or 8/16 bit connection with a PC's motherboard. The 8-bit slot is a single 62-pin connector that supports only 8 bit add-on slave devices. The 8/16-bit connection supports both the 62-pin type and an additional 36 pins on the expansion card. The 16-bit connection type supports additional address space, more DMA channels, more IRQ lines and additional data lines. An ISA bus can execute bus cycles at 8.33 MHz and has an impact on system resources when a card of this type is applied to a local machine connected to a network. The ISA bus is given a higher priority to system resources than other bus connection types (PCI) because of its slower speed. One of the more recent developments of the ISA Bus architecture is the plug-and-play addition to its specifications. This allows the ISA-based expansion card easier to install on machines with an O/S that support plug-and-play.

The ESIA bus was developed to extend the ISA bus architecture to include 32-bit data transmission and 32-bit addressing. An ESIA expansion card uses a special connector that allows it to use a ISA slot without touching the EISA specific signal lines. This connector supports the additional address, data, and control signals needed to use the EISA expansion card. The EISA bus is synchronous, which increases functionality and performance over an ISA bus, which is asynchronous. This type of bus can use the 8/16 bit asynchronous bus of an ISA slot but uses additional bus cycles using the EISA connector. Since EISA supports asynchronous and synchronous bus cycles this allows for backward compatibility in platforms that use ISA expansion cards.

The PCI local bus is designed to provide a processor-independent data path between the CPU and high-speed peripherals. This type of Local bus allows peripherals to be embedded on the motherboard. PCI also can be a slot on the motherboard. With the use of a PCI-PCI bridge controller a motherboard can have up to eight PCI slots to be used for a variety of devices. This type of bus is a standard for DOS/Windows, Macintosh, OS/2 and UNIX platforms. The theoretical throughput of a PCI bus is 132MB/s (32 bit transfer rate) and 264 MB/s (64 bit transfer rate). The PCI bus supports Linear bursts transfers which insures that the bus is continuously filled with data during a burst transfer resulting in higher bandwidth utilization. As mentioned in the section dealing with the ISA bus, the PCI bus utilizes low access latencies. This reduces the time required to gain control of the bus after it has posted a request for a data transfer. PCI also supports bus mastering and concurrency. Bus mastering lets an intelligent peripheral such as a NIC to take control of the bus during data transfer without interfering with the CPU. Concurrency allows the CPU to operate simultaneously while the peripheral does its work, which make for a higher throughput of the system as a whole. PCI is compatible with ISA, EISA and MicroChannel buses. All PCI expansion cards will work in any PCI platform regardless of the processor or expansion bus.

The embedded type of NIC relates directly to the PCI bus. Many manufactures of laptops, workstations, and servers have placed the NIC directly onto the motherboard. The reasoning behind this action is, reduces the cost of buying an additional card, frees up a expansion slot, and insures that the system is network ready with the correct drivers integrated into the OS. The PCI bus is ideal for this type of application for an embedded device. The downside is that should the equipment fail, you do not have the option of just replacing the card.

PCMCIA or PC Card is used primarily in laptop or notebook computers. The PC card utilizes a 68 pin connector that attaches to a laptop computer through a socket on the laptop. The PC card is credit card in size and comes in three varieties, Type I, Type II, and Type III. These three types differ in thickness and classification of operation. Type I is used for primarily for memory and is 3.3mm thick. Type II is 5mm thick and is usually a LAN adapter and/or and modem. Type III is 10.5mm thick and its uses are for components that contain motors like disk drives. The PC card uses a software architecture to provide plug-and-play capabilities, hot swapping of cards, and some use CardBus bus mastering. CardBus is a 32-bit version of the PC card and uses the PCI bus architecture. This allows the PC card to run at 3.3V, supports DMA, 32 bit bus mastering, 32 bit memory slave, 32 bit I/O slave, memory read and write cycles, I/O space read and write cycles, configuration space read and write cycles, and memory reads of multiple, lines, writes, invalidates. The older PC cards that do not use CardBus use a bus that is analogous to the ISA bus specifications.