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...
Auxillary Power Unit (APU) and Ground Power Unit (GPU) is used to mostly to assist the aircraft engines to start. They supply air to Air driven Motor. The motor is mechanically connected to the high pressure compressor assembly of the engine. This starts the engines.