What to WD to buy if I want to back up for dual boot?


Am new here.  Have an iMac now, which has Mountain Lion as main OS and I have Win7 via bootcamp.  i wonder if one external hard drive will do in backing up the files… I know I can use TimeMachine for the Mac OS but am not sure how will I do it when I boot my iMac into Win7.  

Appreciate any comments here.  




If you decide to boot the Mac on Win 7 you can use HFS Explorer to access the drive