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3 Troubleshooting Your PC
Technical Information
IRQs, DMAs, and I/O Addresses Used by Your PC
IRQs used by PC
The IRQ, DMA, and
I/O address
mappings shown
here are for a PC
with a basic
configuration. The
resources used by
your PC may vary,
depending upon
which accessory
boards are bundled
with the PC.
IRQ0 system timer
IRQ1 keyboard
IRQ2 system cascade
IRQ3 free if not used for serial port
IRQ4 free if not used for serial port
IRQ5 free if not used for parallel port
IRQ6 flexible disk drive controller
IRQ7 free if not used for parallel port
IRQ8 real-time clock
IRQ9 available for PCI devices, if not used by ISA board
IRQ10 available for PCI devices, if not used by ISA board
IRQ11 available for PCI devices, if not used by ISA board
IRQ12 mouse
IRQ13 co-processor
IRQ14 integrated IDE hard disk drive controller
IRQ15 free if not used by second IDE controller
DMAs
used by PC
DMA 0 free
DMA 1 free if not used for parallel port in Setup
DMA 2 flexible disk drive controller
DMA 3 free if not used for parallel port in Setup
DMA 4 used to cascade DMA channels 0-3
DMA 5 free
DMA 6 free
DMA 7 free
I/O Addresses
used by PC
170h - 177h, 376h IDE secondary channel
1F0h - 1F7h, 3F6h IDE primary channel
278h - 27Fh (and 3A8h) parallel port
2E8h - 2EFh serial port
2F8h - 2FFh serial port
370h - 371h integrated I/O controller
378h - 37Fh parallel port
3B0h - 3DFh (3B0-3BB,3O0-3DF) integrated video graphics controller
3E8h - 3EFh serial port
3F0h - 3F5h, 3F7h integrated flexible disk controller
3F8h - 3FFh serial port
496h - 497h HP reserved
678h - 67Bh parallel port if ECP mode is selected
778h - 77Bh parallel port if ECP mode is selected