E x p a n s i o n C a r d s
4/4 OWNER’S HANDBOOK
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.
The card’s documentation should list its possible base memory
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 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.
Because
amounts
of memory are usually stated as kilobytes (Kbytes)
rather than in hexadecimal notation, the following conversion table
may be helpful:
4 Kbytes = 1000h
32 Kbytes = 8000h
8 Kbytes = 2000h
64 Kbytes = 10000h
16 Kbytes = 4000h
128 Kbytes = 20000h
