Windows – Why does windows 7 64bit require more disk space/ram

I don't have any special information about the upgrade advisor, but here are a couple possibilities:

1. There's not much reason to use 64-bit unless you're going to have more than 3GB of RAM, as the extra address space won't do much for you. There are some special-case reasons, like high security applications or certain media processing, but in general memory address space is the reason to use a 64-bit OS at the moment.

2. 64-bit OSes DO use more space to store memory addresses, as each address is generally twice as long (this isn't totally precise, but a generalization here will do). This means that storing the locations of data in memory takes more memory itself. Again, however, this isn't really a reason not to use a 64-bit OS, because if you are using one you are probably taking advantage of its increased address space anyway with a decent amount of RAM.

Install and frequently run ccleaner. Defragment your disk (which is probably the biggest). And lastly (if you can), just buy a terabyte external hdd, they are about a 100 bucks and you never have to worry about disk space again :)