Alan Kay's answer to “Did the ENIAC have a BIOS”?

I had Claude Opus disassemble the CDC 6600 dead start panel. The hard part was finding a better image of the switches so the vision could read the bits.¹

The content isn't very interesting, and Claude's comments aren't very detailed. Not bad for 2 minutes of work about a 62 year old computer though. Look out Ken Shirriff, AI is coming for you.²

  Addr   Octal   Instruction      Meaning
  0001   7512    DCN  12          Disconnect channel 12 (put it in a known idle state)  
  0002   7712    FNC  12, 4000?   Send function code to channel 12's device  
  0003   4000?                      └ function code (last bit unclear: 4000 or 4001)  
  0004   7712    FNC  12, 0001    Send another function code
  0005   0001                       └ function code
  0006   7712    FNC  12, 1500?   Send a third function code
  0007   1500?                      └ function code (least certain row)
  0010   2000    LDC  0160?       Load A with a word count
  0011   0160?                      └ the count
  0012   7412    ACN  12          Activate channel 12
  0013   7112    IAM  12, 0015    Read A words from channel 12   into memory starting at 0015
  0014   0015                       └ destination address

1. https://dyninst.github.io/scalable_tools_workshop/petascale2...

2. Not really. I have no idea if this disassembly is corrrect.

3. Quora is prison for words.

EDSAC as early as 1949 had an "initial orders" module. A boot-up ROM. There was a bank of rotary selector switches, to set the octal digits in each ROM word.

David Wheeler (of subroutine fame) figured out the most sensible thing to put in the tiny ROM was a paper tape loader and mini-assembler that loaded the rest of itself from paper tape. So at switch-on the machine would start reading the tape input and run. Programs could be written on the teletype with mnemonics and relative addresses in octal.

It seems a little strange that more advanced later machines like the original PDP-11 from 1970, couldn't "autostart" from ROM like that. You had to toggle in a bootloader.

I think that was because core memory was non-volatile. (EDSAC didn't use core; it had a refreshing DRAM-like delay line memory.) With core, you only had to toggle the bootloader into once and, provided your software didn't accidentally overwrite it, it was still there after a power cycle. So re-toggling in the boot loader was not really that common, despite how much lore surrounds it.

I'm pretty sure Kay's not quite correct about the Eniac not being a stored program computer. In it's original form it obviously was not, as it had to physically reconfigured to solve different problems. However, after the war it was rebuilt to operate like any other stored program (von Neumann architecture) computer, as it was the first recipient of the design philosophy seen in the EDVAC report. It operated in that mode from '48 to '55, when it was decommissioned.

ENIAC in Action: Making and Remaking the Modern Computer is an excellent summary of the initial design and redesign of the Eniac.

Man I didn't even realize that Quora was still around, let alone prominent people still answering questions on it. I deprioritized it in my Kagi searches months ago and even then I didn't notice that much of a change in the quality of my searches.

Alan Kay answering questions on Quora. What a cool gift to the world!

This is one of the thing we lose as more and more of the conversations turn to people privately asking LLMs things, who do their best to scrape out answers from the existing info or make up a best guess. People are losing the ability to ask experts with real, unique knowledge and then share that knowledge with humanity.

The most surprising thing about this to me is Alan Kay answering questions on Quora.

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