Path: utzoo!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!uunet!tut.cis.ohio-state.edu!cs.utexas.edu!asuvax!mcdphx!mcdchg!ddsw1!ddsw1!vpnet!akcs.amparsonjr
From: akcs.amparsonjr@vpnet.UUCP (Anthony M. Parson, Jr.)
Newsgroups: comp.sys.ibm.pc
Subject: Re: distinguishing between MS and IBM(PC) DOS
Keywords: Microsoft C
Message-ID: <25c5ed3d:4260.6comp.sys.ibm.pc;1@vpnet.UUCP>
Date: 31 Jan 90 17:00:07 GMT
References: <6178@uhccux.uhcc.hawaii.edu> <8526@ingr.com>
Lines: 4

Just type
                VER

by itself at any DOS prompt.