I understand that if you install Ubuntu on Windows using Wubi, there are disk performance issues since the entire system is mostly concentrated on a single file.
What about the case of a Virtual Box, will it have improved performance over just installing on Windows with Wubi, or underneath they are the same thing.
Ubuntu running inside VirtualBox on Windows will not have a better performance than Ubuntu installed wihtout separate partition (thus using file on Windows file system). Most likely the performance will be worse.
In the first case, you have a file on Windows FS + virtual machine; In the second case, you still have a file on Windows FS but no virtual machine.