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3.2
BANK SWITCHING
Bank switching is a capability that allows multiple
memory boards to take turns using the same address
region. Different memory "banks" are swapped in and
out of the address region under software control, thus
extending the HORIZON's memory capability beyond the
limitation set by the processor's 16 address bits.
This feature is particularly valuable in a multi-user
environment, for it allows several users to share the
same processor and operating system while maintaining
different
storage for a large array of data that will not fit
into a single memory bank.
Only one bank at a time can respond to a specific
memory reference. Such a bank is said to be "on". A
bank is "off" when it does not respond to reads and
writes from the processor. Although a bank that is off
cannot
processor, the stored data continues to be refreshed,
and remains intact.
3.2.1
Designating Switched Areas
For the purpose of bank switching, the HRAM board is
logically divided into two 32K sections. The first
section includes memory addresses OOOOH through 7FFFH,
and
through FFFFH. Each of
switched when the board is switched on and off, or it
may always remain on, depending upon the configuration
of the jumper plugs as listed in Table 3-1.
HRAM
memory
accept
data
the
second
section
banks.
Bank
from,
or
provide
includes
these sections may be bank
USER/TECHNICAL MANUAL
switching
provides
data
to
addresses
the
8000H
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