I don't think it's proper to call the PS/2 a model, it's a line of computers.
As for the C64, it was an actual model.  Seems to me that were something
like 20 different models of PS/2.
On Sat, 19 Jun 1999, Cameron Kaiser wrote:
  ::> Loaded question: What was the most popular
model of computer
 ::> of all time.  Answer: PS/2. "
 ::
 ::Did it outsell the Commodore C64?
 Unless it sold over 17 million (and that's a conservative estimate), no.
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