You should understand that the "image" you are referencing is just a release level. It does not describe the feature set which is important for picking the correct "part number" or image file. In the sh ver below the C3660-JS-M on the second line shows that this image is for the 3660 platform, the JS is the feature set ( I think its enterprise plus) and the M means something I cant remember without looking up again. Point is to get the correct part number to order you need to know what router you want to put it on and what feature set you need. You can see further down in the show ver that the name of the image file in flash is specific to the platform and feature set.
Cisco Internetwork Operating System Software
IOS (tm) 3600 Software (C3660-JS-M), Version 12.2(3), RELEASE SOFTWARE (fc1)
We are pleased to announce availability of Beta software for 16.6.3.
16.6.3 will be the second rebuild on the 16.6 release train targeted
towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are
looking for early feedback from customers befor...
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