Perl traditionally uses 32-bit integers, but you can have 64-bit integers if your interpreter is configured that way at compilation time. This can break compatibility with pre-compiled modules.

Natively 64-bit systems like Alpha don't need a configuration flag set.

Perl automatically converts to floating point when integers can't hold a value, too.

perldelta for 5.6 has all the nooks and crannies of 64-bitness.

perlnumber has MTYEWTK about numbers in Perl.