When trying to assign more than 3456MB RAM to a Mac OS X Server 10.6.8 guest in 64bit Mode running on a Mac OS X 10.6.8 host the EFI won't initiate the boot process properly. I observed different behaviors depending on the amount of RAM and VRAM I assigned: I need to run a Mac OS X Server 10.6 guest inside Virtual Box for some serious work: I have lots of Adobe Freehand documents, Adobe Freehand was obsoleted by Adobe, there is only a PowerPC version of it. Mac OS X 10.6 is the last version of OS X which support PowerPC binaries through Rosetta Emulation. That means I am stuck with 10.6 but I need to update to 10.9 to run other software like Final Cut Pro and Pixelmator. So the only way to go is to keep Freehand inside a 10.6 guest while updating the host. Sadly having less than 4GB of RAM for the guest is not enough. I appreciate your help very much! Well, I tried it on mine with 8 GB and at least it boots fine. BUT, there is some strange behavior. The 'Activity Monitor' and 'top' reveal only 3.5 allocated. On the other hand, 'About this Mac' and 'System Profiler' report 8 GB. Attaching VBox.log. VirtualBox 4.3.18. I tried the 8 GB RAM / 128GB VRAM setup on 4.3.18 with Mavericks and Snow Leopard. Both booted but it did not allocate the RAM. Looking into top at the host reveals: Fixed in VBox 4.3.20. It will still not work if the ICH9 chipset is selected but this problem is covered by #11103. Source.