RedHat - 32 or 64 bit?

Run command: uname -a

Output from 32 bit host:
Linux hostname 2.6.18-92.el5 #1 SMP Tue Apr 29 13:16:12 EDT 2008 i686 i686 i386 GNU/Linux

Output from 64 bit host:
Linux hostname 2.6.18-92.el5 #1 SMP Tue Apr 29 13:16:15 EDT 2008 x86_64 x86_64 x86_64 GNU/Linux

64 bit systems will have x86_64 in their output and 32 bit systems will not have this flag.