8 ms·

I decided to build a nine-bit computer

180 points by mad_ned 5y ago

googamooga 5y ago
Ternary logic based computer Setun with 9-bit "bytes" was developed in late fifties in the USSR. Not much info on about it in English, unfortunately. https://en.wikipedia.org/wiki/Setun https://en.wikipedia.org/wiki/Setun
- buescher 5y ago
  Ternary on binary systems usually uses a 2-bit "trit" with an extra potential state. That's even how the later Setun machines did it, from what I understand. Oh yes, and the Soviets even developed their own trinary Forth dialect for them.
  - kragen 5y ago
    Even the original Setun machine worked that way, as it turned out, if we believe Willis Ware's contemporary report on Soviet computers.
krallja 5y ago
I hope your address bus is three nonads wide (3^3 bits = 128MiB address space). It would be thematically even better if you used ternary logic, but I’m not sure that FPGA can handle more than two voltage levels.
- tyingq 5y ago
  >I’m not sure that FPGA can handle more than two voltage levels There is a high-Z (high impedance) state you can set I/O pins to for a third state, but no way to detect that high impedance state from the FPGA. It's just used to share an output line with more than one pin. You could make a peripheral that could detect the three states though, with a voltage divider and an analog input.
- mad_ned 5y ago
  haha yes, excellent suggestions! I did think about ternary logic actually but I don't know of an FPGA that supports it. I considered creating like a primitive that burns 2 register bits to approximate it even, and just throw away the 4th state and pretend I have 3-state logic on all the layers above. but i have enough on my hands just trying to get the stupid timing working on a simple CPU. Im not actually a CPU designer so I dont really know what I'm doing lol.
  - enriquto 5y ago
    Throwing away 25% of your bits sound wasteful... what you need is a moderately large power of 2 that is very close to a power of 3. These can be found by computing the continued fraction of log(3)/log(2). The sequence of convergents starts thus 2/1, 3/2, 5/3, 8/5, 11/7, 19/12, 46/29, 65/41, 84/53. Some good choices seem to be 2^8-3^5=13 (loses 5%) or 2^46≈3^29 (loses 2.5%).
    - amelius 5y ago
      You can also detect Z state by driving the input high, reading, then driving the input low, reading. If both reads are different, then you have a Z state. Otherwise, the input is the read state. Of course, drive the input through a resistor.
  - buescher 5y ago
    This is a fantastic hobby project. Have you thought about doing something with the "extra" bit along the lines of tagging bytes for type or garbage collection or whatever like the lisp machines?
JoachimS 5y ago
I was hoping that he was building a CPU that worked on Strong Kleenean logic. https://en.wikipedia.org/wiki/Three-valued_logic https://en.wikipedia.org/wiki/Three-valued_logic
sillyquiet 5y ago
Regarding the interesting bit (to me) in there about the advantages of FPGAs over an SBC like the Pi (speed)- does anybody know of any blogs or projects where an FPGA's speed helped in a hobby project where software running on an SBC wasn't fast enough? I can imagine a few, mostly real-time projects involving expensive computations (image or pattern recognition maybe?), but I would love to see some concrete examples.
- FredFS456 5y ago
  RF/radio is one solid application. Can't really do the signal processing fast enough on an SBC.
  - sillyquiet 5y ago
    Ohh good one. mmRadar projects I guess will fall into this category too.
  - carlsonmark 5y ago
    Not just the signal processing on the received data, but if you want to transmit something, you will probably be using one or more DDS channels to do so. Those may be in the FPGA, or external chips. Either way, if you are mixing the outputs of the DDS, being off by a single clock cycle can cause your transmitted data to be complete garbage. With an FPGA and external DDS chips, this is difficult to do just because of mismatches in PCB trace lengths and/or small temperature fluctuations. With a microcontroller, it is nearly impossible to do even when using DMA because of memory bus contention.
- IshKebab 5y ago
  I think you won't find many because an FPGA that is as fast at computation as a Raspberry Pi will be thousands of pounds. The real advantage is latency and low-level control.
  - tyingq 5y ago
    There are cases where an FPGA is used to make a faster CPU. Old CPUs, of course, but it's still a pretty active niche. There are soft cores for Z80s, 6502, and other old CPUs that run circles around the real hardware.
IshKebab 5y ago
> The answer to why you would still want to build an FPGA system is (and always has been) speed. > So I quickly gave up on creating something that could only exist on my FPGA board I've been doing some FGPA stuff and I think that's the wrong way to look at it. Yes FPGAs are often useful when you need raw speed but that's not the only advantage over CPUs. You also get extremely low latency and direct control of IO pins. With software you are limited to the existing hardware peripherals, but with an FPGA you can make your own!
- horsawlarway 5y ago
  I agree with you. I had a brief stint in hardware design, and an FPGA is almost always going to be worse than dedicated hardware for a task, but it's extraordinarily flexible. Most workflows I saw - you design the hardware on the FPGA (hugely useful for quickly testing and prototyping) then you outsource and actually build a custom chip if you really want speed. It's also a great polyfill tool - since it can take the place of a lot of other hardware peripherals at a moment's notice.
  - bandq 5y ago
    Hey horsawlarway, This is definitely the wrong way to ask but in another thread about the PineNote, you mentioned you have a flow to sync your RM2 to Bookstack -- are your scripts on github or any other place? If not, would you consider making them public or posting on Reddit /r/selfhosted/ and/or /r/RemarkableTablet/ ? I'm new to HN (as a poster, long-time lurker) and I didn't find a way to directly send you a message.
    - horsawlarway 5y ago
      Unfortunately I have not made them public. I'd have to go and clean up a lot of places where I have hardcoded auth. It's not going to be tomorrow (or probably any time in the next month or two) but I have been intending to do the cleanup at some point. If I post them, I'll shoot you a link.
thehappypm 5y ago
Unbelievably tangential but your dog is very cute and I want to see more pictures!
- mad_ned 5y ago
  Wish granted! @the.bessie.report on Instagram
  - errcorrectcode 5y ago
    Hey, we don't need any Aladdin djinns showing off their magical puppers here. Definitely against guidelines and regulations. ;)
  - thehappypm 5y ago
    I love this account! My dog also is a great pup, with some behaviors we’re working on, like barking and reactivity. From the scenery it looks like central MA if I had to guess too!
bronlund 5y ago
onion2k 5y ago
I took my Macbook to pieces and there were lots more than 64 bits.
- errcorrectcode 5y ago
  2^(>64) combinations to put it back together. I find the empty set plus a Hackintosh seems to have fewer bits but work much faster. It must be those repairable qubits.
- selcuka 5y ago
  > I took my Macbook to pieces How did you do that? I couldn't even remove the battery to replace it.
pjdesno 5y ago
Long ago I interned for the group supporting the C-30 ARPANET IMP. At one point the IMP was a 16-bit machine, emulating the old Honeywell (?) minicomputer that the original IMP code was written for. At some point they needed more memory, so they lashed on another 4-bit bit slice, and it became a 20-bit machine. There was an alternate microcode load for it, which implemented an instruction set similar to that of a PDP-11, and could run an ancient version of Unix. (maybe not so ancient back in 1985, but definitely pre-BSD) We used one or two of those for our development machines, and it was my job to write software tools on them, using C with 20-bit words and 10-bit bytes. Man, it was a pain in the ass.
- larsbrinkhoff 5y ago
  The Unix machine was called C70, right?
- googamooga 5y ago
  I have working PDP-11/23 in my possession and last couple of months I’m trying to convince myself that I have enough soldering skills to solder four additional memory lanes on its backplane to increase memory limit from 256KB to 4096KB. Otherwise even though I install a processor able to work with 22bit addresses only 18bit addressing will be available.
- linguistiliniw 5y ago
  IIRC MSP430 microcontrollers do something like that, too. They have low-power 16-bit CPUs, but you can't do a lot with 64k memory space so newer models have instructions with 20-bit addressing. They're fun to work with; some versions have FRAM instead of Flash memory.
  - wildzzz 5y ago
    FRAM is pretty neat. I considered using an MSP430FR5969-SP for a component on a satellite but backed off when I learned more about the destructive read process. We were concerned about a transient bitflip during the write back and had no where safe to store program code other than the FRAM itself. Instead, we went with a RISC-V core in an FPGA and used an 8 channel ADC to cover the telemetry reporting the MSP430 was supposed to handle. I spent a lot of time writing fast, safe code for it so was a little disappointed it never made it into the final design.
bencollier49 5y ago
Related question - is there an FGPA simulator / designer which works on OS X?
- jecel 5y ago
  This one is written in Java: https://github.com/hneemann/Digital https://github.com/hneemann/Digital You can export your project as a Verilog file that can be used in the various FPGA tools.
  - bencollier49 5y ago
    Brilliant, thank you.
einpoklum 5y ago
> I decided to build a nine-bit computer Somehow I was sure that sentence was going to end with "... in MineCraft!"
- IncRnd 5y ago
  Here is a computer created in MineCraft! Wow, it's actually v5.0. The intro starts at 1:22. [1] [1] https://www.youtube.com/watch?v=SbO0tqH8f5I https://www.youtube.com/watch?v=SbO0tqH8f5I
  - einpoklum 5y ago
    8-bit... amateurs :-)
vient 5y ago
See also cLEMENCy 9-bit middle-endian (sic) arch from DEF CON CTF 2017 https://2017.notmalware.ru/89dc90a0ffc5dd90ea68a7aece686544/clemency-201707271159.pdf https://2017.notmalware.ru/89dc90a0ffc5dd90ea68a7aece686544/... (link from https://blog.legitbs.net/2017/07/the-clemency-architecture.html https://blog.legitbs.net/2017/07/the-clemency-architecture.h...)
- nneonneo 5y ago
  Ah, I have fond memories of hacking on that architecture for DEF CON. We wrote a lot of tools for it: by the end (less than 3 days after getting the spec), we had disassemblers, debuggers, binary rewriters, and even rudimentary decompilation support. It was quite a fun journey :)
giovannibajo1 5y ago
Nintendo 64 had a 9-bit RAM (Rambus RDRAM). Only 8 bits of each byte were accessible from the MIPS CPU for obvious reasons; the 9th bit was only used by the GPU (called "RDP") to store extra information while rendering (begin a UMA architecture, the CPU used the same RDRAM used by the CPU). Typically it contained a flag called "coverage" that was used to discriminate pixels on the edge of polygons, that were later subject to antialiasing. By reading back pixels using the CPU, you would be unable to see the coverage flag.
- wolfram74 5y ago
  Yet another weird bit of N64 lore, I'm amazed mupen64 works as well as it does.
  - oh_sigh 5y ago
    > weird bit Quite literally
- klodolph 5y ago
  The 9th bit was also used by the depth buffer. To add to this, the reason that the RAM was available with 9 bits in the first place is so that it could be used to make systems with ECC. It's just that you didn't have to use that 9th bit for error correction, you could use it for extra data, if you designed the system to use it that way.
- phaedrus 5y ago
  Earlier today I was idly wondering: if aliens invented computers and went through the whole 8-bit era, 16-bit era etc. - would they perhaps have developed architectures which had additional "shadow" or "tag" bits on every word? What might they use them for? The idea being maybe an intelligent race with different balance of motivations might not do only the minimum economical thing, instead being willing to trade X% of memory bits or X% of instructions per second or X% more chips for other purposes. For example extra tag bits might be used to encode where the data came from or its datatype, or additional clock cycles between instructions might be used to run a reliability check on the program as it executes, etc.
jacquesm 5y ago
https://en.wikipedia.org/wiki/UNIVAC_1100/2200_series https://en.wikipedia.org/wiki/UNIVAC_1100/2200_series Had a 36 bit word length resulting in a 9 bit 'byte'.
- uvesten 5y ago
  I went way down the rabbit hole on this one. Seems that they are still made and used, fascinating!
  - jacquesm 5y ago
    They are pretty impressive machines. The loadable microcode store is especially interesting, they allow you to emulate an arbitary CPU. Diagnostics in 'IBM' mode was a real possibility on these!
- malkia 5y ago
  I was coming to mention this, though I think my memory goes back to some LISP machine (and was related to car/cdr and related encoding if I'm not mistaken)
- klodolph 5y ago
  36-bit was a common enough word length. Not just UNIVAC, but IBM 360, PDP-6/PDP-10, and some others. Convenient both for octal (multiple of 3 bits) and working with pre-ASCII, 6-bit character encodings (multiple of 6 bits). Which is why we have UTF-9 and UTF-18, as defined in RFC 4042. https://datatracker.ietf.org/doc/html/rfc4042 https://datatracker.ietf.org/doc/html/rfc4042 (Spoiler: It's an April Fool's joke.)
Koshkin 5y ago
Wrote an emulator of a simple 12-bit CPU once, and ran a few examples (coded in binary, of course) on it. It's a fun exercise - highly recommended!
- vba616 5y ago
  Unfortunately, I don't have it anymore, but I was shown a souvenir IBM manual once for a machine with six bit bytes. Probably a 704.
teekert 5y ago
I read it because of the steam powered machine at the top… turns out it’s an fpga.
_nalply 5y ago
When I was bored, I thought about a minimal six-bit computer with a three-byte address bus (18 bit). I went ahead and tried to design a machine language for that computer. There are three registers: the three-byte accumulator, the two-byte stack pointer and a 6 bit wide flag register and these addressing modes: accumulator, immediate, absolute, relative and stack. It's possible that I will try to implement this system with the help of a FGPA. Just out of curiosity. As a hobby.
101010110 5y ago
10008290 5y ago

180 points by mad_ned 5y ago

Ternary logic based computer Setun with 9-bit "bytes" was developed in late fifties in the USSR. Not much info on about it in English, unfortunately. https://en.wikipedia.org/wiki/Setun https://en.wikipedia.org/wiki/Setun

buescher 5y ago
Ternary on binary systems usually uses a 2-bit "trit" with an extra potential state. That's even how the later Setun machines did it, from what I understand. Oh yes, and the Soviets even developed their own trinary Forth dialect for them.
- kragen 5y ago
  Even the original Setun machine worked that way, as it turned out, if we believe Willis Ware's contemporary report on Soviet computers.

krallja 5y ago

I hope your address bus is three nonads wide (3^3 bits = 128MiB address space). It would be thematically even better if you used ternary logic, but I’m not sure that FPGA can handle more than two voltage levels.

tyingq 5y ago
>I’m not sure that FPGA can handle more than two voltage levels There is a high-Z (high impedance) state you can set I/O pins to for a third state, but no way to detect that high impedance state from the FPGA. It's just used to share an output line with more than one pin. You could make a peripheral that could detect the three states though, with a voltage divider and an analog input.
mad_ned 5y ago
haha yes, excellent suggestions! I did think about ternary logic actually but I don't know of an FPGA that supports it. I considered creating like a primitive that burns 2 register bits to approximate it even, and just throw away the 4th state and pretend I have 3-state logic on all the layers above. but i have enough on my hands just trying to get the stupid timing working on a simple CPU. Im not actually a CPU designer so I dont really know what I'm doing lol.
- enriquto 5y ago
  Throwing away 25% of your bits sound wasteful... what you need is a moderately large power of 2 that is very close to a power of 3. These can be found by computing the continued fraction of log(3)/log(2). The sequence of convergents starts thus 2/1, 3/2, 5/3, 8/5, 11/7, 19/12, 46/29, 65/41, 84/53. Some good choices seem to be 2^8-3^5=13 (loses 5%) or 2^46≈3^29 (loses 2.5%).
  - amelius 5y ago
    You can also detect Z state by driving the input high, reading, then driving the input low, reading. If both reads are different, then you have a Z state. Otherwise, the input is the read state. Of course, drive the input through a resistor.
- buescher 5y ago
  This is a fantastic hobby project. Have you thought about doing something with the "extra" bit along the lines of tagging bytes for type or garbage collection or whatever like the lisp machines?

JoachimS 5y ago

I was hoping that he was building a CPU that worked on Strong Kleenean logic. https://en.wikipedia.org/wiki/Three-valued_logic https://en.wikipedia.org/wiki/Three-valued_logic

sillyquiet 5y ago

Regarding the interesting bit (to me) in there about the advantages of FPGAs over an SBC like the Pi (speed)- does anybody know of any blogs or projects where an FPGA's speed helped in a hobby project where software running on an SBC wasn't fast enough? I can imagine a few, mostly real-time projects involving expensive computations (image or pattern recognition maybe?), but I would love to see some concrete examples.

FredFS456 5y ago
RF/radio is one solid application. Can't really do the signal processing fast enough on an SBC.
- sillyquiet 5y ago
  Ohh good one. mmRadar projects I guess will fall into this category too.
- carlsonmark 5y ago
  Not just the signal processing on the received data, but if you want to transmit something, you will probably be using one or more DDS channels to do so. Those may be in the FPGA, or external chips. Either way, if you are mixing the outputs of the DDS, being off by a single clock cycle can cause your transmitted data to be complete garbage. With an FPGA and external DDS chips, this is difficult to do just because of mismatches in PCB trace lengths and/or small temperature fluctuations. With a microcontroller, it is nearly impossible to do even when using DMA because of memory bus contention.
IshKebab 5y ago
I think you won't find many because an FPGA that is as fast at computation as a Raspberry Pi will be thousands of pounds. The real advantage is latency and low-level control.
- tyingq 5y ago
  There are cases where an FPGA is used to make a faster CPU. Old CPUs, of course, but it's still a pretty active niche. There are soft cores for Z80s, 6502, and other old CPUs that run circles around the real hardware.

IshKebab 5y ago

> The answer to why you would still want to build an FPGA system is (and always has been) speed. > So I quickly gave up on creating something that could only exist on my FPGA board I've been doing some FGPA stuff and I think that's the wrong way to look at it. Yes FPGAs are often useful when you need raw speed but that's not the only advantage over CPUs. You also get extremely low latency and direct control of IO pins. With software you are limited to the existing hardware peripherals, but with an FPGA you can make your own!

horsawlarway 5y ago
I agree with you. I had a brief stint in hardware design, and an FPGA is almost always going to be worse than dedicated hardware for a task, but it's extraordinarily flexible. Most workflows I saw - you design the hardware on the FPGA (hugely useful for quickly testing and prototyping) then you outsource and actually build a custom chip if you really want speed. It's also a great polyfill tool - since it can take the place of a lot of other hardware peripherals at a moment's notice.
- bandq 5y ago
  Hey horsawlarway, This is definitely the wrong way to ask but in another thread about the PineNote, you mentioned you have a flow to sync your RM2 to Bookstack -- are your scripts on github or any other place? If not, would you consider making them public or posting on Reddit /r/selfhosted/ and/or /r/RemarkableTablet/ ? I'm new to HN (as a poster, long-time lurker) and I didn't find a way to directly send you a message.
  - horsawlarway 5y ago
    Unfortunately I have not made them public. I'd have to go and clean up a lot of places where I have hardcoded auth. It's not going to be tomorrow (or probably any time in the next month or two) but I have been intending to do the cleanup at some point. If I post them, I'll shoot you a link.

thehappypm 5y ago

Unbelievably tangential but your dog is very cute and I want to see more pictures!

mad_ned 5y ago
Wish granted! @the.bessie.report on Instagram
- errcorrectcode 5y ago
  Hey, we don't need any Aladdin djinns showing off their magical puppers here. Definitely against guidelines and regulations. ;)
- thehappypm 5y ago
  I love this account! My dog also is a great pup, with some behaviors we’re working on, like barking and reactivity. From the scenery it looks like central MA if I had to guess too!

bronlund 5y ago

onion2k 5y ago

I took my Macbook to pieces and there were lots more than 64 bits.

errcorrectcode 5y ago
2^(>64) combinations to put it back together. I find the empty set plus a Hackintosh seems to have fewer bits but work much faster. It must be those repairable qubits.
selcuka 5y ago
> I took my Macbook to pieces How did you do that? I couldn't even remove the battery to replace it.

pjdesno 5y ago

Long ago I interned for the group supporting the C-30 ARPANET IMP. At one point the IMP was a 16-bit machine, emulating the old Honeywell (?) minicomputer that the original IMP code was written for. At some point they needed more memory, so they lashed on another 4-bit bit slice, and it became a 20-bit machine. There was an alternate microcode load for it, which implemented an instruction set similar to that of a PDP-11, and could run an ancient version of Unix. (maybe not so ancient back in 1985, but definitely pre-BSD) We used one or two of those for our development machines, and it was my job to write software tools on them, using C with 20-bit words and 10-bit bytes. Man, it was a pain in the ass.

larsbrinkhoff 5y ago
The Unix machine was called C70, right?
googamooga 5y ago
I have working PDP-11/23 in my possession and last couple of months I’m trying to convince myself that I have enough soldering skills to solder four additional memory lanes on its backplane to increase memory limit from 256KB to 4096KB. Otherwise even though I install a processor able to work with 22bit addresses only 18bit addressing will be available.
linguistiliniw 5y ago
IIRC MSP430 microcontrollers do something like that, too. They have low-power 16-bit CPUs, but you can't do a lot with 64k memory space so newer models have instructions with 20-bit addressing. They're fun to work with; some versions have FRAM instead of Flash memory.
- wildzzz 5y ago
  FRAM is pretty neat. I considered using an MSP430FR5969-SP for a component on a satellite but backed off when I learned more about the destructive read process. We were concerned about a transient bitflip during the write back and had no where safe to store program code other than the FRAM itself. Instead, we went with a RISC-V core in an FPGA and used an 8 channel ADC to cover the telemetry reporting the MSP430 was supposed to handle. I spent a lot of time writing fast, safe code for it so was a little disappointed it never made it into the final design.

bencollier49 5y ago

Related question - is there an FGPA simulator / designer which works on OS X?

jecel 5y ago
This one is written in Java: https://github.com/hneemann/Digital https://github.com/hneemann/Digital You can export your project as a Verilog file that can be used in the various FPGA tools.
- bencollier49 5y ago
  Brilliant, thank you.

einpoklum 5y ago

> I decided to build a nine-bit computer Somehow I was sure that sentence was going to end with "... in MineCraft!"

IncRnd 5y ago
Here is a computer created in MineCraft! Wow, it's actually v5.0. The intro starts at 1:22. [1] [1] https://www.youtube.com/watch?v=SbO0tqH8f5I https://www.youtube.com/watch?v=SbO0tqH8f5I
- einpoklum 5y ago
  8-bit... amateurs :-)

vient 5y ago

See also cLEMENCy 9-bit middle-endian (sic) arch from DEF CON CTF 2017 https://2017.notmalware.ru/89dc90a0ffc5dd90ea68a7aece686544/clemency-201707271159.pdf https://2017.notmalware.ru/89dc90a0ffc5dd90ea68a7aece686544/... (link from https://blog.legitbs.net/2017/07/the-clemency-architecture.html https://blog.legitbs.net/2017/07/the-clemency-architecture.h...)

nneonneo 5y ago
Ah, I have fond memories of hacking on that architecture for DEF CON. We wrote a lot of tools for it: by the end (less than 3 days after getting the spec), we had disassemblers, debuggers, binary rewriters, and even rudimentary decompilation support. It was quite a fun journey :)

giovannibajo1 5y ago

Nintendo 64 had a 9-bit RAM (Rambus RDRAM). Only 8 bits of each byte were accessible from the MIPS CPU for obvious reasons; the 9th bit was only used by the GPU (called "RDP") to store extra information while rendering (begin a UMA architecture, the CPU used the same RDRAM used by the CPU). Typically it contained a flag called "coverage" that was used to discriminate pixels on the edge of polygons, that were later subject to antialiasing. By reading back pixels using the CPU, you would be unable to see the coverage flag.

wolfram74 5y ago
Yet another weird bit of N64 lore, I'm amazed mupen64 works as well as it does.
- oh_sigh 5y ago
  > weird bit Quite literally
klodolph 5y ago
The 9th bit was also used by the depth buffer. To add to this, the reason that the RAM was available with 9 bits in the first place is so that it could be used to make systems with ECC. It's just that you didn't have to use that 9th bit for error correction, you could use it for extra data, if you designed the system to use it that way.
phaedrus 5y ago
Earlier today I was idly wondering: if aliens invented computers and went through the whole 8-bit era, 16-bit era etc. - would they perhaps have developed architectures which had additional "shadow" or "tag" bits on every word? What might they use them for? The idea being maybe an intelligent race with different balance of motivations might not do only the minimum economical thing, instead being willing to trade X% of memory bits or X% of instructions per second or X% more chips for other purposes. For example extra tag bits might be used to encode where the data came from or its datatype, or additional clock cycles between instructions might be used to run a reliability check on the program as it executes, etc.

jacquesm 5y ago

https://en.wikipedia.org/wiki/UNIVAC_1100/2200_series https://en.wikipedia.org/wiki/UNIVAC_1100/2200_series Had a 36 bit word length resulting in a 9 bit 'byte'.

uvesten 5y ago
I went way down the rabbit hole on this one. Seems that they are still made and used, fascinating!
- jacquesm 5y ago
  They are pretty impressive machines. The loadable microcode store is especially interesting, they allow you to emulate an arbitary CPU. Diagnostics in 'IBM' mode was a real possibility on these!
malkia 5y ago
I was coming to mention this, though I think my memory goes back to some LISP machine (and was related to car/cdr and related encoding if I'm not mistaken)
klodolph 5y ago
36-bit was a common enough word length. Not just UNIVAC, but IBM 360, PDP-6/PDP-10, and some others. Convenient both for octal (multiple of 3 bits) and working with pre-ASCII, 6-bit character encodings (multiple of 6 bits). Which is why we have UTF-9 and UTF-18, as defined in RFC 4042. https://datatracker.ietf.org/doc/html/rfc4042 https://datatracker.ietf.org/doc/html/rfc4042 (Spoiler: It's an April Fool's joke.)

Koshkin 5y ago

Wrote an emulator of a simple 12-bit CPU once, and ran a few examples (coded in binary, of course) on it. It's a fun exercise - highly recommended!

vba616 5y ago
Unfortunately, I don't have it anymore, but I was shown a souvenir IBM manual once for a machine with six bit bytes. Probably a 704.

teekert 5y ago

I read it because of the steam powered machine at the top… turns out it’s an fpga.

_nalply 5y ago

When I was bored, I thought about a minimal six-bit computer with a three-byte address bus (18 bit). I went ahead and tried to design a machine language for that computer. There are three registers: the three-byte accumulator, the two-byte stack pointer and a 6 bit wide flag register and these addressing modes: accumulator, immediate, absolute, relative and stack. It's possible that I will try to implement this system with the help of a FGPA. Just out of curiosity. As a hobby.

101010110 5y ago

10008290 5y ago