Source : Webster's Revised Unabridged Dictionary (1913)

Yow \Yow\, pron.
   You. [Obs.] --Chaucer.

Source : Free On-Line Dictionary of Computing

Yow!
     
         /yow/ (From "Zippy the Pinhead" comics) A
        favoured hacker expression of humorous surprise or emphasis.
        "Yow!  Check out what happens when you twiddle the foo option
        on this display hack!"
     
        Compare {gurfle}.
     
        [{Jargon File}]
     
        (1995-03-07)