IRQ Device Assignments

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IRQ Device Assignments | Tech Info Home Page | Hardware Assignments |

Device	IRQ
System Timer	IRQ 0
Keyboard	IRQ 1
Interrupt controller	IRQ 2	...cascaded with IRQ 9
Com2, Com4	IRQ 3
Com1, Com3, Network Cards	IRQ 4
...available / Sound Cards / LPT2	IRQ 5
Floppy Drive controller	IRQ 6
LPT1 Parallel printer port	IRQ 7
...system use (real time clock)	IRQ 8
Cascade with IRQ 2	IRQ 9	Also shared with PCI cards
...available	IRQ 10
...available	IRQ 11	( some Network Cards)
...available or Bus Mouse	IRQ 12
Math co-processor	IRQ 13
Primary Hard Drive controller	IRQ 14
...available / 2nd hard drive	IRQ 15

Note: IRQs 3 and 4 are usually reserved for the COM1 and COM2 ports
When a computer has a modem installed it will want to use one of these 2 settings. Windows 95 and Plug-and-play will try to set the COM port to COM3 or COM4 so it does not conflict with the other internal com ports, but in either case COM3 and COM4 will still have to share the interrupt lines IRQ3 and IRQ4. This will not work. The only safe way is to "disconnect" one of the internal com ports (if you have them) prior to installing the modem. This is usually done by changing a setting in the CMOS/BIOS of the computer.

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