DuckCorp Dico

Found one definition

1.                 From The Free On-line Dictionary of Computing (19 January 2023):
                   
   
   
                   
                     
   box
   Unix box
      <computer> 1. A computer; especially in the construction "foo
      box" where foo is some functional qualifier, like "graphics",
      or the name of an operating system (thus, "Unix box",
      "MS-DOS box", etc.)  "We preprocess the data on Unix boxes
      before handing it up to the mainframe."  The plural
      "boxen" is sometimes seen.
      2. Without qualification in an IBM SNA site, "box" refers
      specifically to an IBM front-end processor.
      [Jargon File]
      (1994-11-29)