To have computers that are anything close to what you'd recognize as a computer today, you'd need to have an electronics industry that's capable of manufacturin

To have computers that are anything close to what you'd recognize as a computer today, you'd need to have an electronics industry that's capable of manufacturing semiconductors, disk drives, CRTs, etc. These rely on many different raw materials which take complex industrial processes to produce. You will probably have to rebuild most of modern civilization (power plants, mines, factories, vehicles, roads, etc.) before you can even think of building computers. Yes, you could build computers out of relays or vacuum tubes, but their computational power would be very limited. You're not going to be able to run Unix on hardware like that. That technology was very slow and had to be repaired frequently (if you have thousands of vacuum tubes, one would burn out every few hours).