virtualbox.org

?You must run a 64-bit version of VirtualBox on that OS
?(Windows Vista, Linux or OpenSolaris).

Does VirtualBox 2.0 for Mac support 64bit guest?

No. 64bit support in VirtualBox depends on VT-x/AMD-V support.
VBox up to 2.0 lacks VT-x/AMD-V support on Macs.

See VirtualBox Manual chapter 1.6 on 64-bit guests

Starting with Version 2.0, VirtualBox also supports 64-bit guest operating systems, under the following conditions:

• 1. You need a 64-bit processor with hardware virtualization support (see chapter 1.2, Software vs. hardware virtualization (VT-x and AMD-V), page 10) and a 64-bit host operating system.
  2. You must run a 64-bit version of VirtualBox on that OS (Windows Vista, Linux or OpenSolaris). This can then run both 32-bit and 64-bit VMs; a 32-bit VirtualBox can only run 32-bit VMs, regardless of the hardware.
  3. You must enable hardware virtualization; software virtualization is not supported for 64-bit VMs.

See chapter 13 (known issues) for current Mac OS X VBox limitations

The following restrictions apply (all of which will be resolved in future versions):

• – No support for audio input
  – No support for VT-x/AMD-V (rarely required)
  – The numlock emulation isn’t implemented yet
  – No support for connecting a virtual serial port to a physical serial port on the host
  – No ACPI information (battery status, power source) is reported to the guest
  – The CPU frequency metric is not supported

[Edit 2008-09-05 09:31GMT]
In other words, there is currently no 64bit (host+guest) binary version for Mac because it would make no sense. You could always have a look into the OSE sources on SVN and even try improve and compile a 64bit Mac Version with VT-x.
[/Edit]

Pray for a Mac-friendly roadmap

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aquarius

As far as I know, the Intel/Mac Version could always be compiled 64Bit (or is there a 32Bit MacOS 10.5 exitsing?)
In fact 64Bit guest would be more than only a toy for me. I am using MacOS and have the need for a 64Bit Linux (OpenSuse) Guest. Are there any plans to support something like that soon...?

The Intel Core Dou's are only 32Bit compatible

The Intel Core 2 Dou's are 64Bit and 32Bit compatible.

The absolute beauty of OS X Leopard is it's ability to run as 64bit or 32bit OS seamlessly without ever worrying about using a 64bit or 32bit application.

Therefore the greatest compatibility range is to support 32bit.

Both Solo and Duo support VT-x hardware virtualization, however I believe there are some mac-mini's that lack the support due to a firmware bug, although it would not matter since thos affected CPU's are not 64bit compatible.