Microsoft stated in their blog post about Windows 8’s native support for ISO and VHD files, if you’re using Windows 8 developer preview you can mount ISO and VHD files and access their contents easily, no more need to rely on third-party programs that mounts ISO images without the need of physical optical drive.
Mounting ISO files in Windows 8
Till now you can’t view and access files in an ISO image, you need to burn it. Now you can, simply right-click on an ISO file in your hard drive and select Mount option or double- click on it, Windows creates virtual CDROM/ DVD drive and its drive letter appears in My Computer for easier access to the contents.
You can access the files much as similar to that of if you had inserted CD/DVD drive into physical optical drive, the speed at which you can access content depends on hard drive speed not the optical drive.
You can virtually eject the virtual drive by right-clicking and selecting eject option and the virtual drive disappears .
Similar to ISO files you can also Mount VHD files (virtual hard disk files) but as new hard drives in in your Computer instead of virtual/removal drive.When you click VHD file, windows creates virtual drive letter pointing to the volume in the VHD and drive icon is same as that of VHD file.
You can eject VHD file by clicking Eject button on the ribbon, changes you made to VHD file will be saved.