interrupt request

Master PIC
IRQ 0 — system timer (cannot be changed);
IRQ 1 — keyboard controller (cannot be changed);
IRQ 2 — cascaded signals from IRQs 8–15; — any devices configured to use IRQ 2 will actually be using IRQ 9
IRQ 3 — serial port controller for COM2 (shared with COM4, if present);
IRQ 4 — serial port controller for COM1 (shared with COM3, if present);
IRQ 5 — LPT port 2 or sound card;
IRQ 6 — floppy disk controller;
IRQ 7 — LPT port 1 or sound card (8-bit Sound Blaster and compatibles).


Slave PIC
IRQ 8 — RTC Timer
IRQ 9 — open interrupt / available or SCSI host adapter; — any devices configured to use IRQ 2 will actually be using IRQ 9
IRQ 10 — open interrupt / available or SCSI or NIC;
IRQ 11 — open interrupt / available or SCSI or NIC;
IRQ 12 — mouse on PS/2 connector;
IRQ 13 — math co-processor or integrated floating point unit or inter-processor interrupt (use depends on OS);
IRQ 14 — primary ATA channel;
IRQ 15 — secondary ATA channel