For IBM PC compatible computers since the early 1980s, here are the default or most common interrupt (IRQ) values or settings and COM Port default settings. * Indicates IRQs that can't be used for general devices.

Common Interrupt Settings	COM Port-IRQ-Base Port Address
IRQ0=System Timer * IRQ1=Keyboard * IRQ2=PIC * IRQ3=COM port IRQ4=COM port IRQ5 =LPT2/Sound card IRQ7=LPT1 Printer IRQ8=RTC * IRQ10=Varies/Video card/PCI IRQ11=Varies/SCSI Cont./PCI IRQ12=Varies/PS2 Mouse IRQ13=Numeric Data Processor * IRQ14= Primary IDE Controller IRQ15= Secondary IDE Controller	COM1 IRQ4 3F8H COM2 IRQ3 2F8H COM3 IRQ4 3E8H COM4 IRO3 2E8H

Notes:
1. LPT2 (second printer port) is usually not used thus it is usually used for the soundcard.
2. Some newer modems will auto-setup on COM5/IRQ10/11 depending on which is free.
3. Some sound cards will auto-setup on IRQ10/11.
4. If you are short of resources, especially with laptops, go into Device Manager and/or the BIOS and disable any Infrared (IR) devices (COM , LPT or other ports, etc.)-most folks don't use them.