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4 BIOS Overview
BIOS Addresses
DMA Channel Controllers
Only “I/O-to-memory” and “memory-to-I/O” transfers are allowed.
“I/O-to-I/O” and “memory-to-memory” transfers are disallowed by the
hardware configuration.
The system controller supports seven DMA channels, each with a page
register used to extend the addressing range of the channel to 16 MB. The
following table summarizes how the DMA channels are allocated.
DMA controller
Channel Function
0 Free
1 Free if not used for parallel port in Setup
2 Floppy disk controller
3 Free if not used for parallel port in Setup
4 Used to cascade DMA channels 0-3
5 Free
6 Free
7 Free
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