My question:
The HPZ220 workstation was originally installed with Windows 2012, and the partition is a GPT partition.
The original system has data partition, the data in the reload system when the requirements can not be lost.
However, after inserting the Windows 2008 installation disk, formatting the original partition or deleting the system partition, select Install and prompt "Windows cannot install to this disk." The selected disk is in GPT partition format, causing the installation to fail.
Workaround: (Refer to the link below)
If it is a HPZ220 workstation, start the workstation, insert the Windows 2008 installation disc, press the F9 key to start the boot option during the self-test, select the HP DVD-ROM option in the boot option in the UEFI boot sources to start the installation of Windows 2008 from the disc boot.
Reference:
HP z230/z220 Workstation, installing Windows7 system with UEFI boot