Mitsubishi Electric Apricot LS Owner's Handbook Manual page 30

Any ports not listed are available for expansion cards. All addresses
below 100h are used by the system board for various fixed system
components and chipset controller settings.
They are unavailable for use.
Base memory address
Some expansion cards are fitted with memory of their own, usually
read-only memory (ROM) containing functional extensions to the
computer's BIOS (basic input/output system) ROM. Some cards also
have random-access memory (RAM).
In order that this memory can be recognised by the system
processor, it must be mapped somewhere within the computer's own
address space. By setting the base memory address you specify
where the card's memory begins within the address space. Typically,
an expansion card's memory must be mapped onto the addresses
between C8000h and EFFFFh in upper memory. With most modern
expansion cards this is fully automatic.
Note
Memory addresses are always written in base 16 or hexadecimal notation.
Unlike the ten digits of the decimal system (0-9), hexadecimal uses sixteen
digits (0-9 and A-F, where A=10, B=11, C=12 and so on up to F=15).
Hexadecimal numbers are denoted either by the suffix "h" or by the prefix
"0x". The final digit of a five-digit memory address is often omitted, so
C8000h may be written as C800h. Since amounts of memory are usually
stated as kilobytes rather than in hexadecimal notation, the following
conversion table may be helpful:
The card's documentation should list its possible base memory
addresses. You will also need to know how much memory the card
has, so that you can leave the right gap between this card's base
address and the next.
4 Kbytes = 1000h
8 Kbytes = 2000h
16 Kbytes = 4000h
S Y S T E M E X P A N S I O N
32 Kbytes = 8000h
64 Kbytes = 10000h
128 Kbytes = 20000h
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