If you have to deal with the older bus types, you may encounter Industry Standard Architecture (ISA) cards. The choice for most desktop systems manufactured after about 1995 was between ISA and PCI. For a traditional Ethernet network running at 10 Mbps or a Token Ring network running at 4 or 16 Mbps, an ISA NIC was more than sufficient. In fact, ISA NICs can be perfectly serviceable on 100 Mbps networks as well, at least for workstations, because the average network user does not require anything approaching 100 Mbps of bandwidth on a continuous basis. The main reason for the ISA NIC being the bottleneck in the scenario described earlier is that it is installed in the server. A server PC that is handling data requests generated by dozens or hundreds of workstations simultaneously naturally requires more bandwidth than any single workstation. In a server, therefore, the use of the fastest bus available is always recommended.
However, there is another element to the bus type decision that you must consider, and that is the availability of expansion bus slots in your computers. Obviously, to install a network interface card into a PC, it must have a free bus slot. Legacy PCs have varying numbers of PCI and ISA slots, and the hardware configuration of the machine determines how many of those slots (if any) are free. Many older “full-featured computers” have peripheral devices installed that occupy many of the bus slots. Because it is possible for a card to occupy a slot without protruding through the back of the computer, simply looking at the outside of a system is not sufficient to determine how many free slots there are. You must open the machine to check for free slots and to determine which types of slots are
available. If no slots are available, an external network adapter using the USB port may be your only recourse.
Administrators of large networks often purchase workstations that do not have all the state-of-the-art features found in many home systems, which may leave more slots free for additional components such as a NIC. In addition, PCs targeted at the corporate market are more likely to have peripheral devices such as audio and video adapters integrated into the motherboard, which also can leave more free slots. However, an office computer may also
use a slimline or low-profile case design that reduces the number of slots to minimize the computer’s footprint.
Even in legacy systems, the selection of the bus type for the NIC should be based on the network bandwidth requirements of the user and not on the type of bus slot the computer has free. However, you may have no other choice than to put an ISA NIC in a computer that could benefit from a PCI card but has only an ISA slot free.