1975 is before my time, but to the best of my knowledge -- backed up with a quick Google -- computers of the time are recognisably similar to computers of today, obviously modulo technological advances. Whereas, if you were to go back a bit further (e.g., pre-silicon, etc.) then people, even experts, would probably find a modern machine somewhat mystical. Anyway, what if we turned things around: What would we think, today, of a computer owned by a time-traveller from 2055? Will there be another "quantum leap" -- possibly quite literally -- like ICs, that will make it an intractable wonder, or will it be basically recognisable?
I bet the software will start to resemble an actual engineering, not like our Moore's law era where the hardware capabilities expanded too fast and the software programmers got a lot of rope for too cheap of a price to value it properly! ...and that the number of cores in a processing unit being close to the number of neurons in a brain maybe?
