If you are willing to wait an infinite amount of time, expend an infinite amount of memory, and restrict your I/O needs to nothing more complex than an infinitely erasable paper tape, then, yes, Perl can "compute anything". That's a rather limited view of "anything", in my opinion. :-)

In the real world, we have real-time applications; Turing-completeness cannot speak to such requirements. Similarly, when trying to access memory mapped I/O, Perl has no native facility that I know of to write to specific memory locations; whereas other languages do. (Even BASIC has it's PEEK and POKE statements!) In Perl, we fall back to using C via XS instead; there is no native "POKE" statement, though unpack with pointers can be used to emulate a "PEEK".

Unless I'm mistaken, this is something that native Perl can't do.