Source : Free On-Line Dictionary of Computing

yoyo mode
     
         The state in which a computer is said to be when it
        rapidly alternates several times between being up and being
        down.  Interestingly (and perhaps not by coincidence), many
        hardware vendors give out free yoyos at {Usenix} exhibits.
     
        {Sun Microsystems} gave out logoised yoyos at SIGPLAN '88.
        Tourists staying at one of Atlanta's most respectable hotels
        were subsequently treated to the sight of 200 of the country's
        top computer scientists testing yo-yo {algorithms} in the
        lobby.
     
        [Is it "yoyo" or "yo-yo"?]
     
        [{Jargon File}]
     
        (1995-03-07)