If your PC don't have a CD/DVD drive (as netbook) or you don't want to buy or write a bootable CD/DVD, you can't boot to your operation system installer or recovery software. Then, an ISO image of that bootable disks and an USB maybe useful for that.
- Prepare your ISO file and an USB which has capacity is equal your ISO expand size. Of course, you must backup your data on the USB
- Open your ISO file with any ISO editor (like UltraISO, MagicISO, . . .). Choose function Write Disk Image and start writing the ISO file to the USB
- Or you open your ISO to USB program (only support Windows installation iso file), choose ISO file dir, check Bootable . . . . and click Burn
Then restart system and you can boot to your software from your bootable USB without CD/DVD.