The Free On-line Dictionary of Computing (30 December 2018):

Microsoft Extended
MSX
MSX-DOS

    (MSX) A Range of computers created in an attempt by
   the industry to create a standard for home computers, similar
   to VHS did with home video.

   The basic MSX machine contained a Z80 CPU working at
   3.58MHz.

   MSX machines were produced by such giants as Sony, Yamaha,
   Panasonic, Toshiba, Daewoo, and Philips.

   The MSX standard was designed by a company called ASCII in
   cooperation with Microsoft who provided a firmware version
   of its BASIC for the machine.  Because this BASIC version
   was an extended version of MicroSoft Basic, it was called
   "MicroSoft eXtended BASIC"; Hence "MSX".

   Microsoft also produced MSX-DOS - a stripped-down version of
   MS-DOS.

   Extensions to the MSX included MSX2, MSX2+ and TurboR.

   FAQ (http://faq.msxnet.org/).

   (1999-02-26)