Apricot XEN Pentium 60, Руководство пользователя

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XEN OWNER'S HANDBOOK A/7
Inside the Apricot XEN
Appendix A
DMA ISA compatible PCs are equipped with a seven channel DMA
channels (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
current task.
On the XEN motherboard only DMA channel 2 is used, the
other six channels are all available for use by expansion cards.
Expansion Some expansion cards are fitted with ROM. Typically expansion
card memory 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
Memory configuration .
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.