Answer: 1.5 tons
Over half a century ago, "Popular Mechanics" provided a generous estimate of future computing status for the time. In the March 1
Where a computer like ENIAC today has 18,000 vacuum tubes and weighs 30 tons, computers may only have 1,000 vacuum tubes in the future and may weigh as little as 1.5 tons.  Although it's easy to smile about yesterday's technological predictions, we can forgive the authors of Popular Mechanics for overly conservative weight estimation. In 1949, computer calculations were performed with vacuum tube arrays. Reducing an array from 18,000 to 1,000 components while maintaining computational power (or even increasing computational power) would require more than just a few advances – the future of computing looked rosy to the authors, albeit still somewhat voluminous. What they could not have foreseen at the time was the advent of the microprocessor.
The invention and the widespread commercial use of the microprocessor in the 1970s changed the amount of space required for arithmetic and triggered a race to continually increase the computational burden Turn on the tiny silicon chips. Now a single microprocessor, millions of times more powerful than ENIAC, can be balanced at the touch of a button, and ultra-light computers and smartphones can be plugged directly into our pockets – without a crane.