I also had not heard of Wubi, and no wonder… It’s strictly an Ubuntu project
Wikipedia Wubi entry
I also had not heard of a loop device (which is different than a loopback device), but after reading up on it, it’s really not different than a lot of things that commonly exist… By definition (Wikipedia loop device entry) a loop device isn’t too much different than mounting an optical device (CDROM, DVDROM, etc), or the filesystem for any virtual technology (eg VMware, Virtualbox, Xen, etc).
So, unlike previous opinions in this thread I can’t agree in general about file permissions performance, it probably won’t be that noticeable on typical Workstations which typically run only one main program at a time anyway.
Totally not described in the Wikipedia entries is what really distinguishes Wubi from paravirtualized systems, but that should be relatively easy to figure out… Whereas paravirtualized systems (eg VMware, Xen, Virtualbox, etc) run in their own isolated space separated from the Host by a hypervisor, Wubi runs in the standard virtual application (User) memory space of the Host machine.
Considering the implications, as I noted before I can’t see any real problem doing that aside from noting the <very> busy processing as all process calls within the wubi VM (again, it’s a standard application VM, not a paravirtualized VM) would be made through the Ubuntu OS, then to the Windows OS, then to the hardware (CPU, RAM, Peripherals).
So, as noted this isn’t suitable for probably even moderate multi-tasking but if you’re interested in doing something relatively small, quick or a relatively light load… It looks OK for me.
That all said, it’s an Ubuntu technology, and understandably highly customized to run Ubuntu. Someone would have to be very motivated to try to modify it for any other distro.
Tony