This is confusing. I have read Microsoft's whitepaper and it said the maximum memory supported is 4GB for 32bit Windows 7 (except for Starter, of course, but we are not interested in that edition.) We have three 32bit Windows 7 PC's. But the memory information on system information page are different. One DELL desktop and another PC that is assembled by me show, "4GB (2.99GB usable)", these are new PC's and they have CORE i5 CPU's, 4GB DDR3 memory installed. Windows 7 Enterprise, Ultimate. One HP desktop shows, "4GB (3.5GB usable)" (it might not be exactly 3.5, but a closer value to it. I can't remember it exactly). This is also a new PC and have a CORE i5 or i7 CPU, 4GB DDR3 memory. Windows 7 Professional. Why do some 32bit Windows 7 say 2.99 is usable and the other 32bit Windows 7 say 3.5 is usable? Is this affected by the motherboard? What is the actual, factual maximum memory of 32bit Windows 7? PS: Yeah, I want to use x64 Windows 7, but I can't because some programs we are using don't work on it.

In your case, using 32 bit Windows, the amount of memory usable by Windows will vary according to the functions included on the motherboard. For a complete explanation, see here: http://blogs.msdn.com/hiltonl/archive/2007/04/13/the-3gb-not-4gb-ram-problem.aspx