A d d i n g E x p a n s i o n C a r d s
Direct memory access (DMA) channelSome hardware devices can use a DMA channel to access system memory without directly burdening the processor. Your computer has DMA channels numbered DMA0 to DMA7.
The following table lists the DMA channels used by the computer. Channels which have no default assignment can be used by expansion cards. Note that DMA3 is free if the parallel port is not configured to ECP mode.
DMA | Default assignment |
DMA0 | - |
DMA1 | |
DMA2 | Diskette/floppy disk controller |
DMA3 | Parallel port in Extended Capabilities Port mode |
DMA4 | System |
DMA5 | |
DMA6 | - |
DMA7 | - |
I/O ports are used by the processor to communicate with hardware devices. Each port appears to the processor as an address low down in its address space.
Some expansion cards are also controlled by I/O ports. The base I/O port address specifies where the card’s ports begin.
The table on the next page lists addresses used by devices on the motherboard. Any ports between 100h and 3FFh that are not listed below may be used by an expansion card.
Motherboard jumper settings determine which I/O ports are used by the
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