Then you'll have to clone the whole disk (the primary one, where you currently have elementary OS) into the external disk.
I've always done this with a live USB/CD, so that's what I recommend you to use. Otherwise, the results may be unexpected (thanks @Xen2050 for the heads-up!).
NOTE: This will delete all data on your external HDD.
Also, a backup of your main disk is strongly encouraged.
Identify the /dev/sdX path of both your main and external drives:
$ sudo fdisk -l
Do the cloning using dd
:
$ dd if=/dev/sdX of=/dev/sdY bs=64K conv=noerror,sync
Replacing sdX
with your primary disk, and sdY
with the external one. Be very sure of that you're writing them correctly, or you could delete/overwrite important stuff!
The additional parameters (bs
and conv
) are the recommended ones by Arch Linux's wiki, you can find more information on what they mean there.
Install Windows on your main drive. Feel free to delete all the stuff in it, it should be in your external disk now (though I'd insistently recommend you to check it before, by trying to boot from the external HDD before doing any deletion).
dd
image of linux to have it still work, you could just usecp
orrsync
etc that copies the files & permissions. I think Windows used to care if it wasn't in the exact same sector of a drive & complain, but linux doesn't mind. But, setting up partitions & grub again can be a hassle, so especially if the new drive is equal or bigger than the old one cloning should work.