SYSTEM EXPANSION

I/O ports

Default assignment

 

 

All addresses below 100h are used by the system board for various fixed system components and chipset controller settings.

They are unavailable for use.

1F0h-1F7h

Hard disk drive controller

200h-207h

Game I/O

278h-27Fh

Parallel port 2

2B0h-2DFh

Alternate VGA

2F8h-2FFh

Serial port 2

378h-37Fh

Parallel port 1

3B0h-3BFh

Monochrome display and printer adapter

3B4h, 3B5h, 3BAh

Video subsystem

3C0h-3C5h

VGA

3C6h-3C9h

Video DAC

3CAh-3DFh

VGA

3F0h-3F7h

Diskette drive controller

3F8h-3FFh

Serial port 1

Base memory address

Some expansion cards are fitted with memory of their own, usually read-only memory (ROM) containing functional extensions to the computer’s BIOS (basic input/output system) ROM. Some cards also have random-access memory (RAM).

In order that this memory can be recognised by the system processor, it must be mapped somewhere within the computer’s own address space. By setting the base memory address you specify where the card’s memory begins within the address space. Typically, an expansion card’s memory must be mapped onto the addresses between C8000h and EFFFFh in upper memory. With most modern expansion cards this is fully automatic.

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