What mode are the Wikipedia OSs running on for the 64 bit machines? Is it 32 or 64 bit mode? We have some 64 bit processors but our hosting provider recommends we run the OS in 32-bit mode unless we require a huge amount of memory - which we don't. Are we missing out on anything by doing this?
we - in my business outside of Wikimedia - are running also 64bit CPUs in 32bit mode.
If you have self-built OSs you can nevertheless make use of all CPU features - except the 64bit adress space of course. It saves some RAM and a lot of software - especially drivers - are not available in 64bit mode.