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3 BIOS Overview
BIOS Addresses
Interrupt Controllers
The Interrupt Requests (IRQ) are numbered sequentially, starting with
the master controller, and followed by the slave.
PCI Interrupt Request Lines
PCI devices generate interrupt requests using up to four PCI interrupt
request lines (INTA#, INTB#, INTC#, and INTD#).
PCI interrupts can be shared; several devices can use the same
interrupt. However, optimal system performance is reached when
minimizing the sharing of interrupts.
IRQ Interrupt Request Description
IRQ0 System Timer
IRQ1 Keyboard Controller
IRQ3 If not used for serial port, available for PCI devices, ISA board, USB port, audio
or video
IRQ4 Used by serial port if enabled. If not, available for PCI devices, ISA board, USB
port, audio or video
IRQ5 If not used for parallel port, available for PCI devices, ISA board, USB port,
audio or video
IRQ6 Floppy Disk Controller
IRQ7 LPT1
IRQ8 RTC
IRQ9 Available for PCI devices, if not used by ISA board, USB port, audio or video
IRQ10 Available for PCI devices, if not used by ISA board, USB port, audio or video
IRQ11 Available for PCI devices, if not used by ISA board, USB port, audio or video
IRQ12 Mouse
IRQ13 Co-processor
IRQ14 IDE Primary channel
IRQ15 IDE Secondary channel. Free unless disabled
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