Is that even possible delay invention of computers to 1990's with 1900 POD? Perhaps one or two decades later is possible. It might be possible delay home computerrs to early 1990's but hardly whole invention of computer.
Very much this. Get a major war, like WW2, and it seems to me that governments, at the very least, will be throwing dollars at research into better and better machines that can do calculations in the interest of code-breaking.
Granted, on the grounds of 'national security' they might possibly clamp down on the spread of any such technology, in case it can be used against their own secret transmissions...