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IRQ Number: 3
16-Bit Priority: 11
Bus Line: 8/16-bit
Typical Default Use: COM2 (second serial port).
Other Common Uses: COM4 (fourth serial port), modems, sound cards, network cards, tape accelerator cards.
Description: This interrupt is normally used by the second serial port, COM2. It is also the default interrupt for the fourth serial port, COM4, and a popular option for modems, sound cards and other devices. Modems often come pre-configured to use COM2 on IRQ3.
Conflicts: Conflicts on IRQ3 are relatively common. The two biggest problem areas are first, modems that attempt to use COM2/IRQ3 and clash with the built-in COM2 port; and second, systems that attempt to use both COM2 and COM4 simultaneously on this same interrupt line. In addition, some devices, particularly network interface cards, come with IRQ3 as the default. In most cases the problem can be avoided by changing the conflicting device to a different interrupt (IRQ2 and IRQ5 usually being the best choices). If the built-in COM2 is not being used, it can be disabled in the BIOS setup, which will allow a modem to stay at COM2/IRQ3 without causing any problems. More general solutions to these issues can be found in the conflict resolution area of the Troubleshooting Expert.