SYSTEM EXPANSION

Direct memory access (DMA) channel

Some hardware devices can use a DMA channel to access system memory without directly burdening the processor. Computers have DMA channels numbered DMA0 to DMA7.

The following table lists the DMA channels used by the computer and shows which are available for use by expansion cards.

DMA

Default assignment

Available?

 

 

 

DMA0

 

Yes

DMA1

8-bit Audio

Optionally

DMA2

Diskette/floppy disk controller

No

DMA3

Enhanced Capabilities Port (default)

Optionally

DMA4

System

No

DMA5

16-bit Audio

Optionally

DMA6

 

Yes

DMA7

 

Yes

Base input/output (I/O) port address

I/O ports are an area of ‘address space’ used by the processor to communicate with hardware devices.

Some expansion cards are also controlled by I/O ports. The base I/O port address specifies where the card’s ports begin. The following table lists the I/O ports used by devices on the motherboard.

Any ports not listed are available for expansion cards.

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