Base input/output (I/O) port address
I/O ports are used by the processor to communicate
with hardware devices. Each port appears to the
processor as an address low down in its address space.
Some expansion cards are also controlled by I/O
ports. The "base I/O port address" specifies where the
card's ports begin.
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
DFFFFh – an area known as the upper memory block
or UMB. You can exclude or reserve UMB regions
with the BIOS Setup utility.
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E x p a n s i o n C a r d s
The card's documentation should list its possible base
addresses. You may 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.
More about memory addresses
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
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.
Because amounts of memory are usually stated as
kilobytes (Kbytes) rather than in hexadecimal
notation, the following table may be helpful:
4 Kbytes = 1000h
8 Kbytes = 2000h
16 Kbytes = 4000h
32 Kbytes = 8000h
64 Kbytes = 10000h
128 Kbytes = 20000h