So I got around to testing this in a Gateway 6400 today.
As I expected, no go. I got two different types of sticks.
One type has 18 Micron branded memory chips on the stick (high
density). That doesn't work. The other type has a bazillion
(or so) much smaller, unbranded memory chips on it. Should be
low density. That doesn't work, either.
So I guess I need to send the stuff back. When I was ordering,
I told the guy I was buying for a Gateway 6400 and he didn't
say much of anything except "OK". I would take that as indication
that they approved the memory for a Gateway 6400. Of course, when
I try to return it they're sure to say "we never recommended it
for a 6400" and charge me some Gawdawful restocking fee, if they
even take it...We'll see...
Kwad