I encountered 2 terms ,"FAT32", a file system and "Windows Vista 32 bit".

I found that the meaning of a 32 bit OS is that that the OS deals with data in chunks of minimum size 32 bits. I don't quite understand the depth of that, but I figure ,every file in that system with that OS should have a minimum size of 32 bits. I also read that these 32 bits are used to hold data of files' location(reference) and details. Which of it is it?

I have also read that 4 GB of RAM is all that is needed at the most if you're on a 32 bit OS. But I don't understand why.

If there are 32 bits to hold info about files and their locations,there can be 2^32 possible combinations of it. But I have found in many places,2^32 is divided by 1024 thrice to get 4GB. Why? Did that 2^32 become equal to 2^32 bytes?

And about filesystems I read a similar explanation for what 32 means in FAT32. It is supposed to mean that 32 bits are used to number file system block. Now how is different from the number before the OS?