What is the maximum memory needed for Windows Vista Business based Compaq Laptop? I have 1.5 Gb RAM installed.

Some motherboards can configure and support over 32 gigs of memory but the operating sytem is what determines how much will be allowed to be used.

All 32 bit operating systems will only allow 4 gigs of memory usage... anything over that is useless. (it is reported that XP only allots for 3 gigs)

64 bit operating systems have no set limits other than by the motherboard it is installed on.

Hope that helps!