while ( <DAT> ) {
    my @line = split( /\t/, $_ );

    while ( @line ) {
        my @four_records = splice( @line, 0, 4 ); # think "4 x shift( @line )"

        push @array_of_arrays, [ @four_records ]; # make this an array containing an array of four elements in each array slot.
    }
}