As the others have identified, x creates the scalars nice and efficiently, and then throws that away by copying it into the scalar, rather than pointing the scalar at the string it created :(

If you're on a version of Perl that supports memory files, here's a technique I use for allocating big strings.

It's more efficent than x in two ways:

1. No duplication.
2. No initialisation.

Of course, the latter may be a downside too.

#! perl -slw
use strict;

our $SIZE ||= 10_000_000;

sub allocBig {
    local $/;
    open my $memFile, '>', \$_[ 0 ] or die $!;
    seek $memFile, $_[ 1 ], 0;
    print $memFile chr(0);
    return;
}


printf 'Check '; <STDIN>;

my $bigScalar;
allocBig $bigScalar, $SIZE;

print length $bigScalar;

printf 'Check '; <STDIN>;

__END__
P:\test>414880
Check 1660/528k
10000002
Check 1888/10376k

P:\test>414880 -SIZE=200000000
Check 1664/528k
200000002
Check 1892/196104k
[download]

Of course, then you face the problem of using it without it getting freed and replaced, but that's what substr and lvalue refs are for :)