virtualbox.org

I have 2 desktop computers
PC1: Intel® Celeron® CPU G540 2.50GHz; MB=Gigabyte GA-H81M-S2H rev.1.0;
PC2: AMD Athlon (tm) 64 X2 Dual Core Processor 5400+ 2.80 GHz; MB=GIGABYTE M61PME-S2P;
Every time I try to create/open a Virtual machine at the PC2, I can select 32 bits OS only. I think this is not normal behavior, because the CPU is 64 bits.

FAQ: I have a 64bit host, but can't install 64bit guests.

Thank you !
After I enabled BIOS setting Virtualization, I can install or open 64 bits OS.