You have just installed the VirtualBox and you are about to setup a new 64 bit operating system. But, from the selections – you realized that only 32 bit operating system are available and no 64 bit operating systems!
If you just select the 32 bit operating system, you will also notify that the tab of Acceleration is greyed out (under the Settings > System).
Solution
Depending on the CPU manufacturers (AMD or INTEL), you will need to activate the Intel VT-x and AMD-V virtualization hardware extensions in the BIOS level. Once done, you will able to see and select the 64 bit operating system.
