Peripheral Reference-"Standard" settings

COM Ports

COMPortIRQ
1$3F84
2$2F83
3$3E84
4$2E83

Parallel Ports

The port address can be any of the following: $278, $378, $3BC.

Monochrome video adapters usually have a parallel port hard wired at $3BC.

If you have more than one parallel port, the BIOS assigns LPT numbers to them from highest to lowest. For example, if a system has ports at $3BC and $278, LPT1=$3BC and LPT2=$278.

Printer ports are set to IRQ 7 in about 85% of cases; the other 15% is IRQ 5.

It is usually safe to share the IRQ with another peripheral, as the IRQ line on the parallel ports are almost NEVER actually used (even while printing).

Sound Cards

When in doubt, tell your software you have a Sound Blaster Pro at the following settings: Port $220, IRQ 5, DMA 1, High DMA 5. If this doesn't work, try a regular Sound Blaster at Port $220, IRQ 7, DMA 1. This will work most of the time. If not, updated drivers may be available for your software. Unfortunately, some programs simply refuse to work with some sound cards at any settings; but this is pretty rare.

IDE Controllers

ControllerPortIRQ
Primary$17014
Secondary$1F015
Tertiary$1E811
Quaternary$16810

IRQ Assignments

IRQAssignmentAvailability
0System TimerNever
1KeyboardNot currently, but maybe when USB catches on
2Slave to 9Linked with 9
3COM2,COM4If you don't have these COM ports, it's probably free
4COM1,COM3Same as for IRQ3.
5Soundcard, parallel portRarely
6Floppy DriveNever
7PrinterCan usually be shared sucessfully
8ClockNever
9MPU-401Sometimes; the MPU-401 on your soundcard can often be disabled
10Quaternary IDEUsually
11Tertiary IDEUsually
12PS/2 MouseUsually in clones, rarely in retail systems
13Math co-processorVery Rare
14Secondary IDESometimes
15Primary IDEOnly in XT or SCSI only systems
The available IRQ's in your system may be already taken up by scanners, SCSI controllers, network cards, or other devices with no real standardization.

Port Assignments

PortAssignment
$0-$FDMA controller
$20-$2FInterrupt controller
$40-$43Timer
$60Keyboard
$61Internal speaker
$70-$71CMOS
$80-$90DMA controller
$94-$9FDMA controller
$A0-$A1Interrupt controller
$C0-$DEDMA Controller
$F0-$FFCo-processor
$168-$16FQuanternary IDE
$1E8-$1EFTertiary IDE
$170-$177Secondary IDE
$1F0-$1F7Primary IDE
$201Joystick
$220Sound card digital audio
$278-$27FParallel port
$2E8-$2FFCOM4:
$2F8-$2FFCOM2:
$330-$337MPU-401
$378-$37FParallel port
$388-$38BFM synthesis (music)
$3B0-$3BBVideo
$3BC-$3C3Parallel port
$3C0-$3DFVideo
$3E8-$3EFCOM3:
$3F0-$3F5Floppy controller
$3F8-$3FFCOM1: