[LinuxBIOS] Ram limit at 128mb Bios, or hardware?

Richard Smith smithbone at gmail.com
Wed Nov 16 22:14:09 CET 2005

> I have a small geode board that has a ram limit of 128MB.  This is
> stated in the doc's, I have not yet been able to test this, yet. If it
> does cap out at 128mb would this be a factor of the bios or the
> hardware, or both?

In general is a hardware limit.  The ram interface is going to be
designed with a specific range of sdram chip density and bus loading
in mind.  At a given density you have to add more chips to the bus to
get more ram. This will increase the bus loading.  The limit should be
set for the maximim loading of the highest density at the maximum

If you purchase high quality ram modules that don't load the bus as
much and have very good matching on pcb you *might* get away with
adding more than the said maximum.  Also If you slow the bus down you
might be able to push the specs.  Over clockers do the inverse of this
all the time.  Getting good quality ram (keeping it good and cold) and
upping the clock rate beyond rated specs.

Density wise you can't normally do a whole lot.  Usually that needs a
new sdram controller.

As with all things in semi-conductors you can probally push the specs
beyond whats on the datasheet but it may not work across all boards.

Richard A. Smith

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