4 ms·

Running a Minecraft Server and more on a 1960s UNIVAC Computer

243 points by brilee 6mo ago

kaladin-jasnah 6mo ago
Hah, I heard about this at VCF East this year, but didn't get to check out the exhibit. There was another MC server demo running on old Macs IIRC. Shame the event was cut short due to a bomb threat.
- feedmittens 6mo ago
  Yeah, I was there on Saturday and could not imagine how it would end the next day. Got to see the Univac powered up but not spitting out those awesome outputs at the time.
proxysna 6mo ago
What a great write up, and a video too! Even though Minecraft stuff ofc was a bit of a bait, it would be interesting see the answer to "Can it run Doom?".
- zimpenfish 6mo ago
  > a bit of a bait "a bit" is doing a lot of work there. It was absolute nonsense. They were no closer to running a Minecraft server than I am to running UKGOV.
  - voidUpdate 6mo ago
    They hosted a program that allowed minecraft clients to connect... I'd class that as a minecraft server, even if it wasn't a very good one
    - proxysna 6mo ago
      Yeah, my thought exactly, execution lacked, but i do admire the attempt.
    - zimpenfish 6mo ago
      > They hosted a program that allowed minecraft clients to connect... Connect in the sense of receiving a login packet and saying "yes". That's it. Steps 1, 2, 3, 9, 10 of [0] (they didn't mention encryption or compression, I'm assuming they didn't implement it.) They didn't mention anything about any of the steps past 10 - again, assuming they didn't implement them. It's a trivial thing they've implemented - good work, sure, but a Minecraft server? Absolutely not. [0] https://minecraft.wiki/w/Java_Edition_protocol/FAQ#What's_the_normal_login_sequence_for_a_client https://minecraft.wiki/w/Java_Edition_protocol/FAQ#What's_th...?
      - creaturemachine 6mo ago
        Not enough dedotated wam for all that.
- voidUpdate 6mo ago
  It could probably run the code for doom, once recompiled for the risc-v emulator, but given that the only output is a paper teletype, displaying it would be a problem
  - Cthulhu_ 6mo ago
    And given the NES emulator example, take half an hour per frame.
  - toast0 6mo ago
    > but given that the only output is a paper teletype, displaying it would be a problem You are in a maze of twisty passages, all alike. A cacodaemon floats by, hissing.
  - kmoser 6mo ago
    I wonder which would be faster: computing a frame, or printing it? If you could print one frame at a time, you could make a flip-book animation.
- jandrese 6mo ago
  Feels kind of like when Usagi Eletric got "Doom" running on a vacuum tube computer with a teletype interface without support for even ASCII, but it was just an imitation of the background music. Anything for the thumbnail.
- egypturnash 6mo ago
  From the article: Only 40,960 words of memory. That’s only 90kb total memory to split between our code and the memory it needs at runtime. Looking at a copy of Doom on the Internet Archive (https://ia800404.us.archive.org/view_archive.php?archive=/15/items/doom_dos/doom.zip https://ia800404.us.archive.org/view_archive.php?archive=/15...), DOOM.EXE is about 709k, and DOOM.WAD is about 11159k. I think that's a pretty solid no. Also it's a 250khz CPU. Not megahertz. Kilohertz. It's slower than the 1MHZ 8-bit home computers like the Apple ][ or c64. "Running" Doom might be possible with some insane hack that offloads storage and/or processing to more modern hardware crammed into the UNIVAC case but given that this is one of two UNIVACs in the entire world, and the only one that actually runs, I don't think the museum is gonna let anyone cram a Raspberry Pi up in there.
- anthk 5mo ago
  Not Doom, but a ZMachine interpreter might run with: - Zork I-III - Calypso - Tristam Island - All the Z3 machine games at IF archive - The rest of Infocom propietary games https://www.ifwiki.org/List_of_Z-machine_interpreters https://www.ifwiki.org/List_of_Z-machine_interpreters Also: https://ifdb.org/viewgame?id=lkr2jf03np19ieix https://ifdb.org/viewgame?id=lkr2jf03np19ieix Now, if the game was libre software it could be improved and ported to Puny Inform (a 'lite' version of Inform6 tuned for smaller machines) creating a really small Z3 file being able to play it from the PDP10 and 8 bit microcomputers to anything from today. From smartphones to PDA's to GNU/Linux with Frotz to Winfrotz and Lectrote and Fabularium for Android/Mac and iOS. So, 'does it run Doom'? Man, you can play Zork in a pen with writting detection. How cool is that?
caminanteblanco 6mo ago
Related: https://github.com/TheScienceElf/UNIVAC-1219 https://github.com/TheScienceElf/UNIVAC-1219 https://youtu.be/rU8sCbwB8XU https://youtu.be/rU8sCbwB8XU
vaughnegut 6mo ago
Favourite article I've read in a while, what a delight. I wonder what kind of performance you could get if someone hand wrote a dedicated, modern C compiler for it.
- voidUpdate 6mo ago
  According to the article, it takes 40 univac instructions to run a single risc-v instruction, so potentially up to 40x the current performance. Though you'd probably need more instructions to do things than a single one, so probably less than that, say 10-20x? Especially if you made a custom compiler that made the best use of the hardware you could, since it's weird
  - commandlinefan 6mo ago
    > it takes 40 univac instructions to run a single risc-v instruction Which is wild, given: > The computer’s original purpose was to be used by the Navy to read in radar signals and direct artillery I'd really be fascinated to see how that was done on such a primitive machine, shame that's probably been lost.
    - mrgaro 6mo ago
      The radar "reading" was done by first plotting analog radar signals to the antique rotary radar displays. Then there would be human operators with a light pen, marking each radar signature on each radar turn. So the Univac would receive input coordinates for each target and track those in memory each turn.
  - dmitrygr 6mo ago
    RISCV is a VEEEEERY poor emulation target - the piecemeal scattering of immediates all over the instr makes it very slow to assemble them (lots of ANDs, shifts, and ORs) . Re-encoding them is one solution, yeah, but then this is a mandatory messy post-compilation step that also needs to know what is code and what is data. It is almost a pessimal setup. MIPS is much simpler to emulate
mghackerlady 6mo ago
I watched the video when it came out, I've been a fan of his stuff for a while. It'd been a while since he uploaded and I was rewatching some of his videos the night before this was uploaded!
Dwedit 6mo ago
"What's My Line" had in-show advertisements for the UNIVAC computer. https://www.youtube.com/watch?v=rEQlOrPs6fw https://www.youtube.com/watch?v=rEQlOrPs6fw
kls0e 6mo ago
beautiful, thank you
petterroea 6mo ago
Stupid question, would a quick&dirty LLVM backend for univac be possible to write, or are there inherent incompatibilities due to its weird architecture?
- mmastrac 6mo ago
  I'm not sure if LLVM would support ones-compliment (does GCC even support that any more?)
djmips 6mo ago
I would like to see this code instead compiled native instead of via the RISC-V interpreter.
deweywsu 6mo ago
WOW! I started off thinking "this could be a boring meandering through registers and op codes" but by the time I got half way through your write-up, I was bouncing off the walls excited. Thanks for sharing your awesome write-up and glad you had such a cool project!
chasil 6mo ago
Research UNIX was ported to the UNIVAC, which (I believe) was the first SMP kernel implementation. It ran on top of the native kernel, known as EXEC-8. A later port to IBM hardware did the same. "The UNIX system for the UNIVAC 1100 series was built as an integrated development environment for transactions that run directly on EXEC. Unlike most other implementations, therefore, it runs not directly on the hardware but as a collection of user-level activities under control of EXEC. These obtain services that would normally be provided by device drivers, and some process creation and management services from EXEC. Any configuration supplied by Sperry, including multiprocessor ones, can run the UNIX system." https://www.nokia.com/bell-labs/about/dennis-m-ritchie/otherports/newp.html https://www.nokia.com/bell-labs/about/dennis-m-ritchie/other...
hassaanr 6mo ago
Incredibly cool project and fantastic write up!
dmitrygr 6mo ago
Give me access to the machine and i'll have linux up on it in a few weeks ;) For real, not just the login prompt
invalidSyntax 6mo ago
"Claude Code can’t write UNIVAC assembly yet" Who knew. It's hard just to look for data on the internet(besides wikipedia).
anthk 5mo ago
Port Scoundrel/Donsol: https://codeberg.org/luxferre/scoundrel-ports https://codeberg.org/luxferre/scoundrel-ports Rules: gopher://hoi.st/0/posts/2026-01-05-discovered-new-game.txt
anthk 5mo ago
On '18 bit words'... if you know some experts on the PDP10, these might help you, they already created new software for ITS and Tops20.
aftbit 5mo ago
Does anyone know why the jal RISC-V instruction scrambles it bits in this way? https://msyksphinz-self.github.io/riscv-isadoc/html/rvi.html#jal https://msyksphinz-self.github.io/riscv-isadoc/html/rvi.html...
- soxfox42 5mo ago
  RISC-V's instruction encoding is designed to keep the bits of literals in common positions between different instruction types. I believe this is to simplify/speed up instruction decoding. The MSB of the literal is always the MSB of the instruction, which makes sign extension consistent. Most of the other bits in the J-type encoding line up nicely with the I-type or U-type encodings.

243 points by brilee 6mo ago

Hah, I heard about this at VCF East this year, but didn't get to check out the exhibit. There was another MC server demo running on old Macs IIRC. Shame the event was cut short due to a bomb threat.

feedmittens 6mo ago
Yeah, I was there on Saturday and could not imagine how it would end the next day. Got to see the Univac powered up but not spitting out those awesome outputs at the time.

proxysna 6mo ago

What a great write up, and a video too! Even though Minecraft stuff ofc was a bit of a bait, it would be interesting see the answer to "Can it run Doom?".

zimpenfish 6mo ago
> a bit of a bait "a bit" is doing a lot of work there. It was absolute nonsense. They were no closer to running a Minecraft server than I am to running UKGOV.
- voidUpdate 6mo ago
  They hosted a program that allowed minecraft clients to connect... I'd class that as a minecraft server, even if it wasn't a very good one
  - proxysna 6mo ago
    Yeah, my thought exactly, execution lacked, but i do admire the attempt.
  - zimpenfish 6mo ago
    > They hosted a program that allowed minecraft clients to connect... Connect in the sense of receiving a login packet and saying "yes". That's it. Steps 1, 2, 3, 9, 10 of [0] (they didn't mention encryption or compression, I'm assuming they didn't implement it.) They didn't mention anything about any of the steps past 10 - again, assuming they didn't implement them. It's a trivial thing they've implemented - good work, sure, but a Minecraft server? Absolutely not. [0] https://minecraft.wiki/w/Java_Edition_protocol/FAQ#What's_the_normal_login_sequence_for_a_client https://minecraft.wiki/w/Java_Edition_protocol/FAQ#What's_th...?
    - creaturemachine 6mo ago
      Not enough dedotated wam for all that.
voidUpdate 6mo ago
It could probably run the code for doom, once recompiled for the risc-v emulator, but given that the only output is a paper teletype, displaying it would be a problem
- Cthulhu_ 6mo ago
  And given the NES emulator example, take half an hour per frame.
- toast0 6mo ago
  > but given that the only output is a paper teletype, displaying it would be a problem You are in a maze of twisty passages, all alike. A cacodaemon floats by, hissing.
- kmoser 6mo ago
  I wonder which would be faster: computing a frame, or printing it? If you could print one frame at a time, you could make a flip-book animation.
jandrese 6mo ago
Feels kind of like when Usagi Eletric got "Doom" running on a vacuum tube computer with a teletype interface without support for even ASCII, but it was just an imitation of the background music. Anything for the thumbnail.
egypturnash 6mo ago
From the article: Only 40,960 words of memory. That’s only 90kb total memory to split between our code and the memory it needs at runtime. Looking at a copy of Doom on the Internet Archive (https://ia800404.us.archive.org/view_archive.php?archive=/15/items/doom_dos/doom.zip https://ia800404.us.archive.org/view_archive.php?archive=/15...), DOOM.EXE is about 709k, and DOOM.WAD is about 11159k. I think that's a pretty solid no. Also it's a 250khz CPU. Not megahertz. Kilohertz. It's slower than the 1MHZ 8-bit home computers like the Apple ][ or c64. "Running" Doom might be possible with some insane hack that offloads storage and/or processing to more modern hardware crammed into the UNIVAC case but given that this is one of two UNIVACs in the entire world, and the only one that actually runs, I don't think the museum is gonna let anyone cram a Raspberry Pi up in there.
anthk 5mo ago
Not Doom, but a ZMachine interpreter might run with: - Zork I-III - Calypso - Tristam Island - All the Z3 machine games at IF archive - The rest of Infocom propietary games https://www.ifwiki.org/List_of_Z-machine_interpreters https://www.ifwiki.org/List_of_Z-machine_interpreters Also: https://ifdb.org/viewgame?id=lkr2jf03np19ieix https://ifdb.org/viewgame?id=lkr2jf03np19ieix Now, if the game was libre software it could be improved and ported to Puny Inform (a 'lite' version of Inform6 tuned for smaller machines) creating a really small Z3 file being able to play it from the PDP10 and 8 bit microcomputers to anything from today. From smartphones to PDA's to GNU/Linux with Frotz to Winfrotz and Lectrote and Fabularium for Android/Mac and iOS. So, 'does it run Doom'? Man, you can play Zork in a pen with writting detection. How cool is that?

caminanteblanco 6mo ago

Related: https://github.com/TheScienceElf/UNIVAC-1219 https://github.com/TheScienceElf/UNIVAC-1219 https://youtu.be/rU8sCbwB8XU https://youtu.be/rU8sCbwB8XU

vaughnegut 6mo ago

Favourite article I've read in a while, what a delight. I wonder what kind of performance you could get if someone hand wrote a dedicated, modern C compiler for it.

voidUpdate 6mo ago
According to the article, it takes 40 univac instructions to run a single risc-v instruction, so potentially up to 40x the current performance. Though you'd probably need more instructions to do things than a single one, so probably less than that, say 10-20x? Especially if you made a custom compiler that made the best use of the hardware you could, since it's weird
- commandlinefan 6mo ago
  > it takes 40 univac instructions to run a single risc-v instruction Which is wild, given: > The computer’s original purpose was to be used by the Navy to read in radar signals and direct artillery I'd really be fascinated to see how that was done on such a primitive machine, shame that's probably been lost.
  - mrgaro 6mo ago
    The radar "reading" was done by first plotting analog radar signals to the antique rotary radar displays. Then there would be human operators with a light pen, marking each radar signature on each radar turn. So the Univac would receive input coordinates for each target and track those in memory each turn.
- dmitrygr 6mo ago
  RISCV is a VEEEEERY poor emulation target - the piecemeal scattering of immediates all over the instr makes it very slow to assemble them (lots of ANDs, shifts, and ORs) . Re-encoding them is one solution, yeah, but then this is a mandatory messy post-compilation step that also needs to know what is code and what is data. It is almost a pessimal setup. MIPS is much simpler to emulate

mghackerlady 6mo ago

I watched the video when it came out, I've been a fan of his stuff for a while. It'd been a while since he uploaded and I was rewatching some of his videos the night before this was uploaded!

Dwedit 6mo ago

"What's My Line" had in-show advertisements for the UNIVAC computer. https://www.youtube.com/watch?v=rEQlOrPs6fw https://www.youtube.com/watch?v=rEQlOrPs6fw

kls0e 6mo ago

beautiful, thank you

petterroea 6mo ago

Stupid question, would a quick&dirty LLVM backend for univac be possible to write, or are there inherent incompatibilities due to its weird architecture?

mmastrac 6mo ago
I'm not sure if LLVM would support ones-compliment (does GCC even support that any more?)

djmips 6mo ago

I would like to see this code instead compiled native instead of via the RISC-V interpreter.

deweywsu 6mo ago

WOW! I started off thinking "this could be a boring meandering through registers and op codes" but by the time I got half way through your write-up, I was bouncing off the walls excited. Thanks for sharing your awesome write-up and glad you had such a cool project!

chasil 6mo ago

Research UNIX was ported to the UNIVAC, which (I believe) was the first SMP kernel implementation. It ran on top of the native kernel, known as EXEC-8. A later port to IBM hardware did the same. "The UNIX system for the UNIVAC 1100 series was built as an integrated development environment for transactions that run directly on EXEC. Unlike most other implementations, therefore, it runs not directly on the hardware but as a collection of user-level activities under control of EXEC. These obtain services that would normally be provided by device drivers, and some process creation and management services from EXEC. Any configuration supplied by Sperry, including multiprocessor ones, can run the UNIX system." https://www.nokia.com/bell-labs/about/dennis-m-ritchie/otherports/newp.html https://www.nokia.com/bell-labs/about/dennis-m-ritchie/other...

hassaanr 6mo ago

Incredibly cool project and fantastic write up!

dmitrygr 6mo ago

Give me access to the machine and i'll have linux up on it in a few weeks ;) For real, not just the login prompt

invalidSyntax 6mo ago

"Claude Code can’t write UNIVAC assembly yet" Who knew. It's hard just to look for data on the internet(besides wikipedia).

anthk 5mo ago

Port Scoundrel/Donsol: https://codeberg.org/luxferre/scoundrel-ports https://codeberg.org/luxferre/scoundrel-ports Rules: gopher://hoi.st/0/posts/2026-01-05-discovered-new-game.txt

anthk 5mo ago

On '18 bit words'... if you know some experts on the PDP10, these might help you, they already created new software for ITS and Tops20.

aftbit 5mo ago

Does anyone know why the jal RISC-V instruction scrambles it bits in this way? https://msyksphinz-self.github.io/riscv-isadoc/html/rvi.html#jal https://msyksphinz-self.github.io/riscv-isadoc/html/rvi.html...

soxfox42 5mo ago
RISC-V's instruction encoding is designed to keep the bits of literals in common positions between different instruction types. I believe this is to simplify/speed up instruction decoding. The MSB of the literal is always the MSB of the instruction, which makes sign extension consistent. Most of the other bits in the J-type encoding line up nicely with the I-type or U-type encodings.