Introduced by IBM, ISA or Industry Standard Architecture was originally an 8-bit bus and later expanded to a 16-bit bus in 1984. When this bus was originally released it was a proprietary bus, which allowed only IBM to create peripherals and the actual interface. Later however in the early 1980's the bus was being created by other clone manufacturers.
In 1993, Intel and Microsoft introduced a PnP ISA bus that allowed the computer to automatically detect and setup computer ISA peripherals such as a modem or sound card. Using the PnP technology an end-user would have the capability of connecting a device and not having to configure the device using jumpers or dipswitches.
To determine if an ISA card is an 8-bit or 16-bit card physically look at the card.
You will notice that the first portion of the slot closest to the back of the card is used if the card is an 8-bit card. However, if both sections of the card are being utilized the card is a 16-bit card.
Today many manufacturers are trying to eliminate the usage of the ISA slot however for backwards compatibility you may find 1 or 2 ISA slots with additional PCI slots, AGP slots, etc. However, you may also not have any ISA slots. We highly recommend when purchasing any new internal expansion card that you stay away from ISA as it has for the most part disappeared.