I think he means the "External Device" option from the create timers screen. It can function like the VCR timer or Auto-Tune options. However, "External Device" displayed at "Ext" on the timers create screen, is designed for compatible external devices that will allow the box to turn on the external recording device while the show is recording and turn it off when the program ends or in other ways control that external recording device.
It is connected by the analog outputs for recording.
This external device option was really designed for the old PocketDish external recorders (manufactured by Archos but no longer available), but it still supports the latest generation of Archos portable recorders that are designed to function with Dish Network equipment. These hand held recorders can record Dish Network programming directly onto its hard drive. Then all you have to do is take it with you and play back all your favorite programs wherever you are. The latest Archos with Dish Network can now perform high-speed transfers from the DVR HDD to the recorders HDD using the USB 2.0 connection The largest screen size for the players available today is 7". Think of it like the iPod playing video etc. That kind of thing.
Go to the Archos website and learn more and the Dish website tech portal may also have some info.