An 8051-family microcontroller, the CPU architecture that's found almost everywhere - including space. I wonder if they're running Forth too, as this old discussion I found also mentions 80C32 and RTX2010 together with Forth:

https://groups.google.com/d/topic/comp.lang.forth/7PK44n68I_...

So if HN has any questions, this is a good time to ask them. The hangout is here:

https://plus.google.com/u/0/115269917987589859757/posts

These are 16-bit chips (the Novix addressed 128 KB) that use dedicated stack memories, that's 3 ports to memory total. The RTX puts the stacks on chip.

The nice thing about these CPUs is they can do stack, alu, and return in parallel, interrupts are cheap, timings are predictable, and programming model is nice if you like Forth. One disadvantage of the design is that clock rate is limited. RAM fetch and instruction processing have to fit between pulses meaning RAM has to be approx twice as fast as clock.

Still, it's telling of the industry's regard for Forth that the manufacturer itself manages to misspell the language as "Fourth" in the chip's official product page.

> The file holding the interpreter was labeled FORTH, for 4th (next) generation software - but the operating system restricted file names to 5 characters.

http://www.colorforth.com/HOPL.html

It was the OS for the IBM 1130: http://en.wikipedia.org/wiki/IBM_1130

Because it was the cheapest computer IBM had at the time, it got used by a lot of young pioneers in their salad days.

Redundancy's definitely one solution, which is one reason why spacecraft tend to have multiple processors and/or processors with redundant logic pipelines. They also tend to use different substrates that are harder for cosmic rays to effect, different, more expensive, casings that offer more shielding, and also larger, older, more vetted processes. For example, this chip is uses a 1 micron process, which is a lot bigger than the process used in current cpus, which means that there's a lot more mass in the transistors to soak the effects of radiation, making it harder to cause damage.

The smallest integrated circuit is a diode, it has 1/2 transistors :). OK, a diode is not actually an integrated circuit, but if you can use a material to make a diode, you probably can use the same material to make an integrated circuit with enough money, time and ingenuity.

Some of the diodes are made of germanium. It has a very low band gap, that is useful for "crystal radios" ( http://en.wikipedia.org/wiki/Crystal_radio#Crystal_detector ). Perhaps this can be useful to make very low voltage CI, to reduce the power and heat. But perhaps there is a technical problem that I don't know.

The diodes in the LED have many semiconductors. The band gap of the material is related to the color ( http://en.wikipedia.org/wiki/Light-emitting_diode#Colors_and... ). With this you could make high voltage CI (like 10V?). Perhaps it may reduce the noise ratio??? But perhaps there is a technical problem that I don't know.

[kens: If you are reading this, I'd love to see a technical post about this subject.]

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Edit: According to Wikipedia, one of the first CI was made of Germanium: http://en.wikipedia.org/wiki/Integrated_circuit#Invention

> Half a year after Kilby, Robert Noyce at Fairchild Semiconductor developed his own idea of an integrated circuit that solved many practical problems Kilby's had not. Noyce's design was made of silicon, whereas Kilby's chip was made of germanium. Noyce credited Kurt Lehovec of Sprague Electric for the principle of p–n junction isolation caused by the action of a biased p–n junction (the diode) as a key concept behind the IC.

So nearly 2 orders of magnitude price difference. In 1998 admittedly, but still. (Someone should come up with a better example for the Wikipedia article)

Other users have answered the question, but I'd like to add a little more information. http://en.wikipedia.org/wiki/LED_circuit#LED_as_light_sensor

> As a photodiode, an LED is sensitive to wavelengths equal to or shorter than the predominant wavelength it emits. For example, a green LED is sensitive to blue light and to some green light, but not to yellow or red light.

If you want to measure the light of all visible wavelength, you must use a semiconductor with a low band gap, for example the named in the other comments: Germanium, Silicon or Gallium Arsenide

It's interesting to read the table in http://en.wikipedia.org/wiki/List_of_semiconductor_materials... but it's important to sort it by band gap fist, o you an compare the applications of semiconductor with a similar band gap.

There are even more exotic examples to think of. Eyes turn light into electricity without (AFAIK) Silicon. Maybe part of that physics/chemistry can be practically used elsewhere?

Correct. A photon hits a chromophore bound to an opsin protein, and flips the chirality of the chromophore from 11-cis to all-trans, which changes the structure of the opsin protein, which starts the cascade of activity leading to sight. We could definitely use chemical detectors to take advantage of this or a similar process.

Nerve impulses are not electricity. There is a moving charge gradient which is not the same as an electric current.

Large "scientific" CCD's benefit from large geometries (typ. 25 micron pixels), which probably contributes to radiation hardening. But it's hard to protect a chip from radiation without keeping it in the dark.

There's also the fact that silicon has received such refinement thanks to the overall semiconductor industry.

One issue with only using redundancy to overcome errors from radiation is you'll have a hard time determining which processor has an error - especially when several processors are affected at the same time.

https://www.pmddtc.state.gov/regulations_laws/documents/offi...

So mass market products aren't made radiation-hard. Rad-hard CPUs more modern than that FORTH engine exist; Atmel makes a rad-hard SPARC. But they're produced in tiny quantities and are thus very expensive.

http://bernd-paysan.de/b16.html

http://www.greenarraychips.com/

Nice to see this neat-but-underappreciated architecture in the news.

It's already appreciated. Let me recall here the 'scientist' character (A&B Srugatsky) who explains the World as a huge inertial mass to the good or evil in the same.

Tertium non datur it is a principle of our mind sometimes used in computers.

http://www.intersil.com/en/products/space-and-harsh-environm...

How do they do this? They're lying. Various Alibaba vendors list literally every part number they can find as something they are selling. If someone wants it, then they see if they can actually get it.

In any case, the real price for the RX2010 was between $1000 and $10,000 according to this thread I found from 1999: http://www.strangegizmo.com/forth/MISC/msg01281.html

http://users.ece.cmu.edu/~koopman/stack_computers/index.html

The RTX2010 has had its own wikipedia entry too since 2008 : http://en.wikipedia.org/wiki/RTX2010

Actually in this thing the top two elements of the stack are held in registers. So if you wanted to use the ANSI C compiler instead of FORTH, you might just think of it as a two-register machine (there are actually quite a few more) with a few special stack-manipulation instructions.

How that compares on a practical level, I have no idea. But it's one of the reasons the JVM has a stack-based model and no registers: it makes writing compilers for JVM byte code a lot easier.

In terms of compiler writing, if you wanted to write any optimisations you'd probably want to manipulate 3-address code internally, if only because the data flow based analyses would be made easier (and then you would emit stack code in the last step).

This might be a reason why the JVM designers decided to use a stack machine, but I doubt it's an important one - they'd easily be able to get ahold of a few decent compiler writers if they needed to.

https://en.wikipedia.org/wiki/Graph_coloring

http://research.ihost.com/lcpc06/final/7/7_Paper.pdf

Actually, here's the original for sale, but the abstract doesn't explicitly mention being NP-complete.

http://www.sciencedirect.com/science/article/pii/00960551819...

The biggest disadvantage is their performance because it's hard to make them do operations in parallel.