Fairchild Symbol Computer

Well, here’s something you don’t see every day.

The Fairchild Symbol Computer.

Fairchild’s Symbol computer had both the compiler and operating system built with hardware, not software.


Wow, that’s quite the machine! Some 10000 chips, by the sound of it, and in the late 60s. And the memory controller does everything from demand paging to garbage collection.

A very interesting approach. Doing it all in hardware, and in a much better way than the (referenced) later IAPX32 of Intel.

Also, it never quite worked. OS, Compiler, TextEditor in gates? Do you have any idea how difficult it is to fix a bug in your compiler or OS with a soldering iron? Any idea how to ensure there are no bugs to begin with

The one-and-only version built still exists in the Computer History Museum back rooms; I’ve seen it.


You use TECO and program with your text editor.
Text editing is not hard logic wise, just use a new card coding form.
It also makes the key punch girl happy.

I suspect the motive was still from the punched cards batch era,
In goes the cards, out punches the program or the results,
depending on just what the symbol computer does.
Makes computer scence easy, none of this mouse or password stuff;
just use the correct hole in the wall: programs:input:output:bribes

I was talking about debugging the hardware, since the compiler is in hardware - not ROM, but in gates, Fixing bugs means cutting traces, unsoldering chips, soldering and wiring up new ones, etc, and sometimes it meant designing a new circuit board, procuring parts, worrying about timing…
Slow, not for the faint of heart, and no one could do anything else while it was being fixed.
Totally stupid idea.


It would have been worse, if they’d been successful - the idea, as I understand it, was to replace the 10,000 logic chips with a smaller number of custom LSI chips. I suppose you’d have to call the result a computing appliance - it behaves as-shipped. In fact, perhaps we could think of this as extreme early-binding, whereas the best ideas seem to be around late binding.

Fixing bugs means cutting traces

My guess it was on wire wrapped panels, easy to change a connection, or add spare gate.
PCB’s where mostly flip chip sizes, for the late 60’s,for mass production.

computing appliance - it behaves as-shipped

This would never do in real life. No modern program behaves as shipped, or expected.
There is never a bug in a program, just a new feature.

Doing it gates is a different model than regular computing, just more work to get it right.

Nope, you guessed wrong.
No wirewrap, all tightly packed (blue) PC boards full of dual inline TTL, with edge connecters on 3 (yes!) sides- which is tricky.
The head of the project was the inventor of the dual inline package and the zero insertion force connectors which made it possible to have edge connectors on more than 1 side.
Maybe the backplanes (and sideplanes) were wire wrapped, but you still need to cut/jump traces on the PC board.
Really ugly. Never worked after years of trying.

Still for that scale of chips,it is impressive, working or not.
I wonder if could get a FPGA version working?

Nice! I never quite got to visit the CHM - got quite close, but it was closed that day. Unlikely to travel that way again.

The CHM was closed at least one “sample day” in February 2022. Not sure about more recently. I imagine they’ve been suffering a shortage of old-timers like us to staff the place.

Maybe now is the time to beg/borrow/buy a team of robots to cruise around the exhibits on our behalf and let us “visit” the museum through their eyes. Wheels seem expensive. Drones are cheap. You just need an air traffic control system.

What Fairchild needed was (okay, maybe with the help of a time machine) access to a “silicon compiler” and a hardware simulator. I wonder if anyone has written a useful compiler in Verilog and burned it into an FPGA. (Yes, yes, let me Google that for you…).

Addendum: a minute later appears one path: FpgaC - Wikipedia
The problem with hardware-based compilers, I can see already: recursive descent. But with the right coding style and a stack, it should be doable. The original Bell Labs C compiler was probably very small, BTW. A minimal BASIC interpreter fits in 1,500 bytes of C code, heavily macro-iced. But we already know you can implement an interpreter in hardware.

Computer science has state based versions of compilers everywhere. Never a comple version,
as students have to finish that on thier own. Forth also decomposes nicely into a simple computing machine. The symbol computer may be just a demo version, ample to comple a simple program
but not a large one as memory was quite dear in the 1960’s.

As noted by Ben, a chapter (“SYMBOL: A Large Experimental System”) in one of Gordon Bell’s books:

Also not far away:
Fairchild Symbol Computer by Stanley Mazor (4 pages)