I have two Windows installations on a single machine: Windows 7 and Server 2008 and have to regularly switch between them. However it takes a lot of time to start all applications needed to start working on each one.
So I thought, maybe it was possible to (for example) hibernate W7, but then somehow start Server 2008 and when finished working there return to the last state of W7 waking it from hibernated state.
Unfortunately I was unable to find solution to this using search.
It is probably not a good idea to do this if any of the partitions in use by the hibernated system are also used by the other system: when the hibernated system wakes up its disk is going to have magically changed, and may well be seen as having errors.
The Windows bootloader automatically restarts the hibernated system, if there is one, so the two Windows systems cannot share a bootloader. You will need a third bootloader to choose between the two Winodows bootloaders.
The method: In turn, make the partition of each Windows installation active, and do a repair of the bootsystem so that each system can boot itself.
Install a Linux system, using Linux's grub bootloader to select between the installed operating systems. The installation procedure will add entries for both of the Windows systems alongside the Linux system.
You could load one OS into a virtual machine (there are many: VMWare, VirtualBox, VirtualPC, etc.). These generally let you save the current state of a running VM and restart it (or you could hibernate it).
I'm not sure if any of the Windows VMs let you boot an existing partition though, so this is just a partial answer for you.
This isn't possible. Hibernation, sleep, etc. are basically the same as shutting down but to a different degree of "down".
They're low-level commands that use a system baked into the machine BIOS, called ACPI. There are ACPI "states". I don't remember specifically but gnerally: state 1 = off, 2 = CPU power, 3 = CPU+RAM power, 4 = full power. The friendly names "sleep", "off", etc. map to these. These states are implemented at the BIOS level, in between OS and hardware, and are associated with the machine itself, not the OS. Therefore, for example, if you put an OS into sleep mode, it's actually shutting hardware off.
This would only work if the ACPI layer were being emulated (as in virtual machines). You could install VMware and run the two concurrently, or use a desktop VM system like VirtualBox (both are available for free).
