How to find a machine is 32 or 64 bit

Normally we confuse between whether a CPU or OS is 64/32 bits.. Here is some clarity. 

Linux :
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To find kernel is 64 or 32 bit:
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shell # uname -a
Linux vscn1u.rchland.ibm.com 2.6.18-92.el5 #1 SMP Tue Apr 29 13:16:15 EDT 2008 x86_64 x86_64 x86_64 GNU/Linux

If "x86_64" or "ia64" is mentioned, it means the kernel(OS) is 64 bit, otherwise its 32 bit.

To find whether a CPU is 64 or 32 bit :
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1) shell # grep flags /proc/cpuinfo

    In the output if you see
    1. rm means: 16 bit processor
    2. tm means: 32 bit processor
    3. lm means: 64 bit processor

 2) shell # getconf LONG_BIT
     The output will say directly whether the processor is 32 or 64 bit.

Windows :
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To find whether the OS is 32 or 64 bit :
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For Windows XP / Vista / Server 2003 :

Find whether window is 32 or 64 bit

For windows 7 :
1. Right click Computer -> Properties
    .. This will open up a window
2. Look at System Type field. It will directly say whether window 7 is 32 or 64 bit.