There is a special variable $. that always contains the current line number of the file you are reading, starting with one. This can be used as the index for your two parallel arrays:

use strict;
use warnings;
use Data::Dumper;
my @array;
my @arraynew;
while(<DATA>){
  chomp;
  ( $array[$.-1], $arraynew[$.-1] ) = split ' ', $_, 2;
}
print Dumper \@array, \@arraynew;
__DATA__
1 http:/abcd efgh/
2 http:/
[download]

Update 1: corrected split statement as per comments below.

Update 2: another version based on regexes instead of using split:

use strict;
use warnings;
use Data::Dumper;
my @array;
my @arraynew;
( $array[$.-1], $arraynew[$.-1] ) = /^(\S+)\s(.*)/ while <DATA>;
print Dumper \@array, \@arraynew;
__DATA__
1 http:/abcd efgh/
2 http:/
[download]

This will work if
    ( $array[$.-1], $arraynew[$.-1] ) = split;
is
    ( $array[$.-1], $arraynew[$.-1] ) = split ' ', $_, 2;
(see below).

---

Give a man a fish:  <%-(-(-(-<

split takes an optional third argument which says how many elements to split the string into, so it will work for your purposes:

my $line = "1 http:/abcd efgh/";
my($number, $address) = split ' ', $line, 2;
# $number now contains "1";
# $address now contains "http:/abcd efgh/";
[download]