"It's not about an undo button," writes Slashdot reader marcle, sharing an article by a senior member of the technical staff at Sandia National Laboratories who's studying advanced technologies for computation. "Just reading this story bends my mind." From IEEE Spectrum: [F]or several decades now, we have known that it's possible in principle to carry out any desired computation without losing information -- that is, in such a way that the computation could always be reversed to recover its earlier state. This idea of reversible computing goes to the very heart of thermodynamics and information theory, and indeed it is the only possible way within the laws of physics that we might be able to keep improving the cost and energy efficiency of general-purpose computing far into the future... Today's computers rely on erasing information all the time -- so much so that every single active logic gate in conventional designs destructively overwrites its previous output on every clock cycle, wasting the associated energy. A conventional computer is, essentially, an expensive electric heater that happens to perform a small amount of computation as a side effect...

[I]t's really hard to engineer a system that does something computationally interesting without inadvertently incurring a significant amount of entropy increase with each operation. But technology has improved, and the need to minimize energy use is now acute... In 2004 Krishna Natarajan (a student I was advising at the University of Florida) and I showed in detailed simulations that a new and simplified family of circuits for reversible computing called two-level adiabatic logic, or 2LAL, could dissipate as little as 1 eV of energy per transistor per cycle -- about 0.001 percent of the energy normally used by logic signals in that generation of CMOS. Still, a practical reversible computer has yet to be built using this or other approaches.
The article predicts "if we decide to blaze this new trail of reversible computing, we may continue to find ways to keep improving computation far into the future. Physics knows no upper limit on the amount of reversible computation that can be performed using a fixed amount of energy."

But it also predicts that "conventional semiconductor technology could grind to a halt soon. And if it does, the industry could stagnate... Even a quantum-computing breakthrough would only help to significantly speed up a few highly specialized classes of computations, not computing in general."

intellitech shares a report from Engadget: For those of you who miss the iPhone headphone jack, you're definitely not alone. But Strange Parts creator Scotty Allen missed it so much that he decided to add one to his iPhone 7. He just posted a video of the project's entire saga, with all of its many ups and downs, and in the end he holds what he set out to create -- a current generation iPhone with a fully functional headphone jack. It turns out, real courage is adding the headphone jack back to the iPhone. The project took around 17 weeks to complete and throughout it Allen spent thousands of dollars on parts including multiple iPhones and screens and handfuls of lightning to headphone adaptors. Along the way, Allen bought a printer, a nice microscope and fancy tweezers. He had to design his own circuit boards, have a company manufacture multiple iterations of flexible circuit boards and at one point early on had to consult with a chip dealer that a friend hooked him up with.

The final product works by using a lightning to headphone adaptor that's incorporated into the internal structure of the phone. However, because the headphone jack is powered via the phone's lightning jack with a circuit board switching between the two depending on whether headphones or a charger are plugged into the phone, you can't actually listen to music and charge the phone at the same time.