If you do have another drive that can boot Windows 7, you can use the Disk Management tool to build a new system partition on your existing SATA drive. You have to shrink the existing partition, and create a new partition. Then you can copy the boot files to the new partition using bcdboot.
An APU is an auxiliary power unit. On-board APUs are small jet turboshaft engines that are started to provide electrical and hydraulic power to the aircraft when needed during periods when the engines aren't running. Some aircraft are designed...
In a nut shell, an APU is onboard power for an aircraft, usually a small turbine in the tail, a GPU is just what the initials stand for, ground power for the aircraft. The main difference is one is portable and one is built in. The ground unit never leaves the ground.