This question, and questions of a general Unix nature are not appropriate
for this newsgroup.  Direct them to comp.unix.questions or other 
comp.unix groups.  However, since these questions do occur frequently, 
here is a brief summary of responses:

Submitted by Randolph J. Herber, paraphrased here:

Unix came first...

Unix was written before MS-DOS, which is a distant relative, tracing some
of its roots to Unix, but also incorporating other influences.  According
to _The Bell System Technical Journal_ (Vol. 57, No. 6, July-August, 1978
``Forward''), "The UNIX story begins with Ken Thompson's work on a
cast-off PDP-7 minicomputer in 1969." According to _The MS-DOS
Encyclopedia_ (Microsoft Press), page 19, MS-DOS "ran on the prototype for
the first time in 1981."

The abbreviations... 

The primary causes of the abbreviations were the 10 characters per
second terminal speeds and the small system memories (e.g. 128KB).

Although Microsoft based some of MS-DOS on Unix, they also incorporated 
elements of CP/M and other sources.  For this reason, some commands are
identical to Unix, while others are different.