virtualbox.org

windows 2008 enterprise can
after installed vbox 5.04 on Win 2012 Host and upgrade guest 2008 enterprise, the memory 2008 in guest machine set down to < 3582 MB.

I discover the session Information:
configuration indicate OS Type: Windows 2008 (32-bit)

but

Runtime Information:

Guest OS Type: Windows Vista (32-bit)

I solved the problem by set the windows 2008 X64 and reinstalled guest.