I am the owner, as I had long suspected, but only found out for sure very recently, of a most remarkable little hand calculator I bought back in the mid-eighties: a programmable Scientific Calculator HP 15C.
This particular calculator, one of a series of models, was produced by HP from 1982 through 1989, can be used to write in it and then save for their later use, subroutines involving numerical integration, matrix multiplication and inversion, trig functions (direct and inverse), logarithms, rise numbers to powers and, or find their square roots and to do other usual operations in engineering R&D and for scientific number crunching.
Having always had access to regular computers, I have had little use for these functions, except for the direct and inverse trig functions, logarithms, exponentials and roots. I often use it to check results when running tests on the software I need to write, for example to figure out if certain ideas of mine, or of someone else, are feasible or not in practice. Case in point: just now I have been imagining a mission with a very little and cheap (in terms of “normal” space prices, that is) kind of satellites that are all the rage now days, known as “cubesats” because of their usual shape, with several deployed in each of a number of equally spaced orbit planes, so I needed to figure out, among other things, how many of those planes would be enough to do the intended job and how long it will take to deploy the little satellites until all the planes are occupied and in the desired configuration. For that I wrote a program to find out and used my trusty old calculator for doing much of the checking of the results.
As I was doing that I had this thought: “Listen Oscar, you have been using this thing for over thirty years and have not changed its batteries for at least 15, maybe 20 years. How is that even possible?”
So I first looked for orientation in old and trusty Wikipedia, and found the whole story there, as well as an explanation of the amazing long-life of the tiny batteries it uses:
https://en.wikipedia.org/wiki/HP-15C
The secret is that the integrated circuit, or chip, in this calculator was made using a silicon-on-sapphire technique, where the usual silicon, before etching the electronics on it, is first deposited on top of a sapphire layer, where it bonds to it so the sapphire then provides a very strong insulation to all the electronic components, so much less of the batteries charge is wasted in leakages from them:
https://en.wikipedia.org/wiki/Silicon_on_sapphire
As to what are the MOS or MOSFET transistors? Here is an explanation for the technically minded. They are probably the most usual kind of transistor now in use and have been that for a long time. What changes over time is their ever decreasing size:
https://en.wikipedia.org/wiki/MOSFET
As for those who have this little wonder but no longer also the manual, here is a place to get one in PDF format:
http://www.hp.com/ctg/Manual/c03030589.pdf
Ex-Windows user (Win. 98, XP, 7); since mid-2017 using also macOS. Presently on Monterey 12.15 & sometimes running also Linux (Mint).
MacBook Pro circa mid-2015, 15" display, with 16GB 1600 GHz DDR3 RAM, 1 TB SSD, a Haswell architecture Intel CPU with 4 Cores and 8 Threads model i7-4870HQ @ 2.50GHz.
Intel Iris Pro GPU with Built-in Bus, VRAM 1.5 GB, Display 2880 x 1800 Retina, 24-Bit color.
macOS Monterey; browsers: Waterfox "Current", Vivaldi and (now and then) Chrome; security apps. Intego AV
