Apple Service Diagnostic tests the hardware for correct operation. Apple Service Diagnostic (EFI) performs low-level tests of hardware directly and does not require an operating system to run. Apple Service Diagnostic OS tests use an OS X operating system to perform tests.

The models this ASD is used for are:
iMac (21.5-inch, Mid 2010)
iMac (27-inch, Mid 2010)

This is in 3 DMGs directly from Apple, they can not be combined until final burning to disk or USB key as the bless commands embedded will look for the next DMG.

Directions:
1) unzip
2) keep all DMGs in the same folder or all on your desktop! (they need to be in the same directory)
3) Use disk utility to burn onto DVD, refer to the manual inside first DMG on how to install ASD onto flash drive