Is Unix running in 32-bit or 64 bit?

In Solaris:

You can determine the currently running kernel with this command:

/usr/bin > /usr/bin/isainfo -kv
64-bit sparcv9 kernel modules
/usr/bin > isainfo -v
64-bit sparcv9 applications
        asi_blk_init vis2 vis popc
32-bit sparc applications
        asi_blk_init vis2 vis popc v8plus div32 mul32

This machine is able to run 64 bit applications, thus it has a 64 bit kernel running. If you only saw a 32-bit response or even "Command not found" then you are running with a 32 bit kernel.

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In Linux:

>uname -a
Linux linux-machine 2.6.18-194.8.1.el5 #1 SMP Wed Jun 23 10:52:51 EDT 2010 x86_64 x86_64 x86_64 GNU/Linux

>uname -m
x86_64

If it prints i686 then your kernel is 32 bit, if you see x86_64 then it's 64 bit,