| The 4100 uses the size of the first memory option to decide the overall
"system configuration" size. Any smaller memory options appear
replicated some number of times depending on the ratio of the small
option size to the "system configuration" size.
For example, if you have a single 1 Gbyte option and two 512 Mbyte
options, then the 512 Mbyte options will show up twice.
In this example:
location 0 to 1.0 Gbyte will be in the big option
location 1.0 Gbyte to 1.5 Gbyte will be in the first small option
location 2.0 Gbyte to 2.5 Gbyte will be in the second small option
but in addition
location 1.5 Gbyte to 2.0 Gbyte will be a duplicate of locations
location 1.0 to 1.5 Gbyte so that writes to location 1.0 Gbyte will
also change location 1.5 Gbyte.
Similarly location 2.5 Gbyte to 3.0 Gbyte will be a duplicate of
locations 2.0 to 2.5 Gbyte in the second small option.
The operating system already has support for "bad pages" to avoid using
memory that it thinks is broken. In the scenario above, this mechanism
is used to mark the duplicate memory as "bad" so the operating system
won't try to use it. It's not really bad, of course, it just
represents non-existant memory.
I'm not sure whether the system will have two holes of "bad memory" or
just one. One version would be to notice memory from 0 to 2.5 Gbyte
with one hole from 1.5 to 2.0 Gbyte. Another option would be to notice
memory from 0 to 3.0 Gbyte with two holes (1.5..2.0 and 2.5..3.0).
I'm not sure how much memory will be reported (2.0 Gbyte, 2.5 Gbyte or
3.0 Gbyte depending on whether holes are ignored and whether a hole at
the end is treated differently).
Note that if the "small" option were even smaller, say 256 Mbyte then
it would get replicated 4 times (1 usable and 3 duplicate copies) if
the large option were still 1 Gbyte.
I'm not a 4100 expert and am extrapolating from other stuff in the
note and of how system's I've seen before work. I may have got some of
the details wrong.
P.S. in the 4100 case an "option" is really two cards. They are
installed in pairs and both boards of a pair must be the same size.
Steveg
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