ok...
1. suspending is hibernating, it just happens on the mac side. otherwise, closing the VM after suspending or disconnecting the external drive as i often do would cause big problems. when you suspend your virtual machine, the contents of memory are written to the disk and the machine is placed in a "power off" state.
2. suspending parallels (Virtual Machine -> Suspend) is not the same as "Sleep" from the Windows Start Menu. "Sleep" on the windows side puts your machine in a low power state, but remains on and allows some background threads to continue to execute.
3. to enable hibernate on windows: (from windows knowledge base)
- Click Start, and then type cmd in the Start Search box.
- In the search results list, right-click Command Prompt, and then click Run as Administrator.
- When you are prompted by User Account Control, click Continue.
- At the command prompt, type powercfg.exe /hibernate on, and then press ENTER.
- Type exit and then press ENTER to close the Command Prompt window.