1. What is the difference between MER and APA?
MER is the Machine Edition Runtime. This is a compiled version of the application that is running in your PV terminal. This file type cannot be edited.
APA is the APlication Archive. This is essentially a zipped version of the development version of your application. This file also cannot be edited.
There is a third file type that doesn't really get mentioned, but it is the most important. The MED is the Machine Edition Development file. This is what you open and work on in FactoryTalk View Studio. You can only edit the MED file.
When I do my development (MED) and want to send it to the PanelView, I create the runtime (MER) file and load it into the PV. There is also a tool to convert the MER back to a development (MED). This was not always the case in earler versions. And today, developers have the option to not allow this. That way I can't connect to your PV and "steal" your application. Very important to small companies or a 1 person shop.
If I am doing development and want to send you a copy of the whole project to review, I would create the application backup (APA) and send that to you. You can then "restore" that file and you will have the same project. But I could also send you the MER.
MED ==> MER = Create Runtime
MER ==> MED = Restore Runtime
MED ==> APA = Backup
APA ==> MED = Restore
2. Should I backup both?
From a developers point of view I would make a point to backup the MED (APA). But from a user's point of view, I would backup the MER.
If a user has a backup to the MER they could potentially reload it into a PV without needing any software. In the past, the restrictions on the MER meant that backing it up didn't get you much. Today though, with the ability to restore the MER file into a development copy (MED) means that it is a good item to backup and makes the APA a bit less important.
3. Are these files already automatically saved under a specific folder or do I have to force an archive?
The MER and APA files can be located wherever you wish on your PC. They don't have to go to any specific location. The MED on the other hand must be located in a specific folder and they do not give you any option to put it anywhere else (don't bother backing up the MED). There is no automatic backup that takes place. Manual only.
OG