PHP process 32 v 64 bit virtual memory

Looking for some explanation (and verification) as to why the virtual memory increases by 5 fold (at the minimum) from 32 bit to 64 systems. I'm aware (for the most part) of the int, struct, etc changes from 32 to 64 bit. Results from running php -r 'sleep(1000);' & on 32 and 64 bit systems are below. PHP was built by hand. 32 bit System => Linux kronos 2.6.18-194.el5 #1 SMP Tue Mar 16 21:52:43 EDT 2010 i686 Build Date => Sep 22 2011 08:50:40 Configure Command => './configure' '--prefix=/opt/php' Test: php -r 'sleep(1000);' & root 4863 0.0 0.1 7064 1064 ? Ss 08:21 0:00 /usr/sbin/sshd root 5403 0.0 1.0 17736 11048 ? Ss 08:28 0:00 \_ sshd: root@pts/1 root 5418 0.0 0.1 4540 1488 pts/1 Ss 08:28 0:00 \_ -bash root 2340 0.0 0.3 13240 3288 pts/1 S 08:53 0:00 \_ /opt/php/bin/php -r sleep(1000); root 2341 0.0 0.0 4224 872 pts/1 R+ 08:53 0:00 \_ ps axuf 64 bit System => Linux ceous 2.6.18-194.el5 #1 SMP Tue Mar 16 21:52:39 EDT 2010 x86_64 Build Date => Sep 22 2011 08:51:02 Configure Command => './configure' '--prefix=/opt/php' Test: php -r 'sleep(1000);' & root 5181 0.0 0.1 62608 1220 ? Ss 08:22 0:00 /usr/sbin/sshd root 5724 0.0 1.5 102020 15620 ? Ss 08:27 0:00 \_ sshd: root@pts/1 root 5726 0.0 0.1 66064 1608 pts/1 Ss 08:28 0:00 \_ -bash root 2019 0.0 0.4 88864 4200 pts/1 S 08:54 0:00 \_ /opt/php/bin/php -r sleep(1000); root 2021 0.0 0.0 65592 924 pts/1 R+ 08:54 0:00 \_ ps axuf 32 v. 64 virtual memory difference: 75624 Thanks!