64bit Windows Perl has 64 bit integer support (quad ints or quads in pack's docs). 32bit Perl has 53 bit integer support because floating points dont start rounding numbers until 2^53 is reached. Less XS modules work/compile on 64bit windows than on 32bit windows. Not sure if modern X64 CPUs run faster in 32bit or 64bit mode. Remember 64bit Perl will use a significantly more amount of memory because of 64bit integers and 64bit pointers being used everywhere. Its difficult for me to think of scenarios where Perl would need more than 2 GB of memory (max amount of address space a 32bit program can use on Windows, most apps will crash in 32bit 3GB mode due to signed/unsigned errors with pointers, I've heard on PerlMonks Perl will crash in 3GB mode). Is Win64 Perl a beta product? Absolutely not. Are there differences which would make 32 over 64 better? yes, but there are also differences which would 64 better than 32.