According to Spaceflight 101, the chamber pressure is the same, but the expansion ratio (throat area to end-of-nozzle area) is 7 times larger in the vacuum variant, which (if correct) implies about 2.7 times the nozzle diameter if the throat is unchanged.
The Wikipedia description of the 1C-vacuum says the expansion nozzle length is 2.7 meters, while the overall length of the first-stage 1C is only 2.9 meters long - roughly half of that being nozzle. So the nozzle length is basically doubled. Presumably the relationship between the 1D and 1D vacuum is analogous.
This pic is said to be, left to right: Falcon 1 Merlin 1C, Falcon 9 1C (different mounting), and Falcon 9 2nd stage 1C vacuum - without the extension nozzle, so it's a shorter, fatter nozzle than the others.
Source: space.stackexchange.com
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Its a software informer from Microsoft.