"Running Virtualbox 4.3.20, with matching Virtualbox Extension pack. I have a late model i7 laptop, so I thought I'd try the VBoxManage command. C:\Program Files\Oracle\VirtualBox>VBoxManage modifyvm OSX_Yosemite -cpuidset 00 000001 000306a9 00020800 80000201 178bfbff Oracle VM VirtualBox Command Line Management Interface Version 4.3.20 (C) 2005-2014 Oracle Corporation All rights reserved. Usage: VBoxManage modifyvm <uuid|vmname> [--name <name>] [--groups <group>, ...] [--description <desc>] [--ostype <ostype>] [--iconfile <filename>] [--memory <memorysize in="" mb="">] [--pagefusion on|off] [--vram <vramsize in="" mb="">] [--acpi on|off] [--pciattach 03:04.0] [--pciattach 03:04.0@02:01.0] [--pcidetach 03:04.0] [--ioapic on|off] [--hpet on|off] [--triplefaultreset on|off] [--hwvirtex on|off] [--nestedpaging on|off] [--largepages on|off] [--vtxvpid on|off] [--vtxux on|off] [--pae on|off] [--longmode on|off] [--synthcpu on|off] [--cpuidset <leaf> <eax> <ebx> <ecx> <edx>] [--cpuidremove..." - martin english