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Since the last version we have now installer part 1 and part 2, but both are the same installer (64bit), just that second "part" is named as if it was the 32 bit installer.

Then we also have the right 32 bit installer, which is smaller than the 64 bit one.

So: 64 bit installer part 1 and part 2 are the same 64 bit installer, repeated, just with different name and down the correct 32 bit installer (smaller than 64 bit one):

setup_prison_architect_64_12b_(13214)_(g).exe -> "Prison Architect (Part 1 of 2)" (460MB)
setup_prison_architect_32_12b_(13214)_(g).exe-> "Prison Architect (Part 2 of 2)" (460MB)

And also:

setup_prison_architect_32_12b_(13214).exe->"12b (32-bit installer)" (341MB)

I know it's a little error, but it can be confusing and as no one has reported this... Please, GOG, can you fix that when you can? Thank you very much!
Whats the difference 32 vs 64 installers ? And yes downloads are confusing. what to pick ? or if i need to patch earlier version. will the patch work
Yeah, noticed this problem, too. And the 64bit-installer (I guess) installs GOG Galaxy without asking for permission or anything:

Yes, the download page says:
Prison Architect (Part 1 of 2) 12b 460MB
Prison Architect (Part 2 of 2) 12b 460MB

yet they behave like:
Prison Architect (complete 32-bit version) 12b 460MB
Prison Architect (complete 64-bit version) 12b 460MB

However, the 64-bit version causes a System Error:
The program can't start because VCRUNTIME140.dll is missing