Why IBM got MS started?

["L.Goulet" <aminfo@java.dyn.ml.org>]

  Hello all,
  
  Like I stated before, this is the info list, so here I
  go with another question! ;-)
  
  I have that book on my desk, it says:
  
  IBM           (it was published by IBM in September 1983)
  Disk
  Operating
  System
  Technical References
  by Microsoft Corp.
  
  It is the IBM-DOS 2.10 Technical References book.
  
  As I remember it, MS haven't done anything before that 
  (except IBM-DOS 1.X and 2.0X, I presume).
  
  Why did IBM get MS started by giving them this first big
  contract? 
  
  Today, it seems strange. Maybe IBM figured it would be cheaper
  to have MS writing it for them. I cannot imagine that IBM didn't
  have the knowledge to do it themselves.
  
  What was Bill Gates doing in 1983? Has he ever written code or did
  he have some very qualified people with him back then? If so, what have
  those people become?
  
  We all know that later, MS was allowed to sell DOS themselves under
  the name MS-DOS.
  
  Can anybody refresh me on that? 
  
  I don't say this was good or bad, because should IBM have had all the
  rights on DOS, what OS the first PC-clone makers would have put in their
  machines? 
  
  I am just curious about what drove IBM to that decision back then.
  
  L.Goulet