Advantages of the PCI bus over the ISA bus
The high-performance PCI bus has both speed and interrupt-sharing advantages over the ISA bus.
- The ISA bus implementation is based on edge-triggered interrupts. In computer electronics, everything is either 0 or 5 volts. Edge-triggered interrupts look for the transition (edge) from 0 to 5 volts or vice-versa. This makes it difficult to share interrupts because the PC may be busy when the transition (trigger) occurs. If so, the edge is not recognised and the request is not processed.
- The PCI bus, however, provides level-triggered interrupts that see if the voltage is at 0 or 5 volts. Interrupt requests are always serviced no matter when they occur. This advantage means that a card in a PC bus will always outperform a similar card in an ISA bus.