How to find 32bits or 64 bits OS/CPU/Application information?

This one is really very interesting topic. Most of the time, people ask about what is my OS type (is it 64 bit OS or 32 bit OS) because in any case they need to buy/download/install compatible applications or OS or databases. In this post, there are three sections to find out about OS, CPU and application bits information.

Remember that if everything is good at OS side and still problems with installation of application or databases, it may be because of incompatible type (32 vs 64 bits) of application/database!

For OS:

In Linux:
# uname -a
Linux srv32bits 2.6.9-11.ELsmp #1 SMP Fri May 20 18:26:27 EDT 2005 i686 i686 i386 GNU/Linux

# uname -a
Linux srv64bits 2.6.9-42.ELsmp #1 SMP Wed Jul 12 23:32:02 EDT 2006 x86_64 x86_64 x86_64 GNU/Linux

Note: In case of Linux, check for the green colored text. 
1) i686/i586/i486/i386 describes a 32-bit kernel.
2) x86_64 describes a 64-bit kernel.

In Solaris:
coming soon  :-)