Source : Free On-Line Dictionary of Computing

Baby AT
     
         The redesigned {AT} motherboard that had the same
        size as the {XT} motherboard had (8.5" x 11") and could thus
        fit into an XT case.  The original 12" x 13" AT motherboards
        are now largely forgotten.
     
        Compare {ATX}.
     
        (1997-02-20)