VirtualBox - upgrading Windows XP VMs to 2 CPU

Symptom: If you had Windows XP VM with only 1 CPU created / virtalized earlier you won't be able to see a second CPU when you add it later.

1. Make sure you have second CPU added via VM Virtual Box Manager and "Enable IO APIC" checkbox  in System settings on Motherboard tab is checked.
2. You should see 2 CPUs in Device Manager , but when you run Task Manager, you'll see only 1 CPU.
3. MS recommendation for Windows XP is to reinstall Windows (no surprise) as you can see it in this KB article: http://support.microsoft.com/kb/309283
4. Do not reinstall Windows, just run run the following from command prompt

rundll32 syssetup,SetupInfObjectInstallAction ACPIAPIC_MP_HAL 128 %windir%\inf\hal.inf

5. Reboot when prompted , log on back to Windows XP wait until you see "Windows has finished installing new devices. The software that supports your device requires that you restart your computer. You must restart your computer before the new setting will take effect" and press OK to reboot it again.

6. Done

Extpart.exe error "Unable to connect to C: or it does not exist"

When you try to expand C: drive using extpart.exe you get the following error:
"Unable to connect to C: or it does not exist"

Here are some workarounds you can try:

1. Close Windows Disk Management console. It's using Logical Disk Management service which extpart.exe is using.
2. Make sure there are no snapshots
3. Stop some non-essential services i.e:

• Windows Search
• File Replication service
• DFS Replication service
• Perfect disk PDEngine service

4. Reboot computer in safe mode and then run extpart.exe