you can always use Modules like Math::BigInt

Excellent observation - and such large numbers are, after all, stored in scalars - as per the OP's requirement.

The one limitation of Math::BigInt is that it's pure perl and can therefore be a little slow when it comes to manipulating those numeric values. As an alternative one could look at modules like Math::GMP, Math::Pari and Math::MPFR. These modules, like Math::BigInt, all store their values in sclarars and they still suffer from the "available memory" limitation - and, unlike Math::BigInt, they all depend upon external C libraries. The one big difference in their favour is that they provide much faster arithmetic manipulation of the bignum values than Math::BigInt.

Cheers,
Rob