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    Kinda neat how Microsoft went full circle…

    1978-1980: Unix
    1980-2000: DOS
    2000-2009: Emulated DOS
    2009-2016: PowerShell (plus Emulated DOS)
    2016-today: Linux (plus PowerShell and Emulated DOS)
    
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      According to wikipedia, Xenix was first released in 1980 with the last release in 1989.