Dose anyone know where to download WIndows 8 free ISO?

Commonly Windows 8 ISO is used for burning the downloaded Windows 8 steup file indo DVD or CD. Yesterday one friend told me that Windows 8 ISO is a single file with the suffix as “*.iso”. It looks like a zip file under Windows 8. Windows 8 ISO is, sometimes, useful to repair the crashed system, whose safe mode is also crashed. Besides, burning Windows 8 ISO into DVD or CD is much better than saving it in hard drive, cause it is big to ocuppy the space.

Now my problem is where to download Windows 8 free ISO for there are so many download resources so that do not know which one is best.

many thanks in advance.