Refer to the table above, and the documentation supplied with
the card to establish which IRQ, if any, to use and how to select
ISA compatible PCs are equipped with a seven channel DMA
(Direct Memory Access) controller. This DMA subsystem
allows peripherals to access motherboard memory directly.
Without the DMA subsystem every memory access would
have to involve the processor. Using DMA, peripherals can
access memory without stopping the processor executing its
On the motherboard DMA channel 2 is used by the floppy
controller and channel 3 by the Enhanced Capabilities Port,
the other channels are all available for use by expansion cards.
Expansion card memory
Some expansion cards are fitted with ROM. Typically
expansion card ROM contains extensions to the motherboard
BIOS providing additional functionality.
Expansion card ROM (sometimes known as slot ROM) must
be addressed somewhere in the processor's memory map. An
area of the memory map of an ISA compatible PC is allocated
for expansion card ROM.
If you are unfamiliar with the concept of memory maps, and
the hexadecimal numbering system the following text attempts
to explain them. If you are familiar with the memory map of
an ISA PC then continue to Configuring expansion ROM.
Numbers and computers
For a variety of reasons, in computer literature and
terminology, numbers are sometimes in hexadecimal notation
rather than the decimal that we are all familiar with.
Hexadecimal is a long word and it is often shortened to hex.
Inside your computer
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