it wasn't
the first
 portable by a long chalk but which one does everyone remember? 
  Since the first portable was the Hyperion and  I have  a
 basement full of them, I'm hoping that people have long memories.
  
 I think the first one to "call" itself a "portable" was the
"IBM 5100
Portable Computer" - circa 1975 (although I think there might have been
a 1950s computer that also called itself a "portable" in that you could
move it around on a truck).
-W