‹ BackHN Continuity

Thread

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

188 points · 74 comments · midnightfish

  1. coldpie · · focus · HN ↗
    Somewhat tangential, I've watched a bunch of videos on YouTube from @deramp5113 about the Altair 8800 and other early microcomputers, which feature a similar set of front panel switches for dialing in your initial program. One thing that's interesting to me, as someone who learned computing in the late 90s, is how much is expressed in octal instead of hex on these early computers.

    As shown in the linked picture, the byte pairs are divided into [4 groups of 3] instead of [3 groups of 4] switches, which I would find more comfortable as a hex-reader. I believe, maybe someone can confirm, that octal notation is easier to translate into bits than hex is. We just don't do either of those things terribly often anymore, so octal has mostly fallen out of favor, perhaps because it groups less nicely into multiples of 8.

    Nowadays I almost never think in octal. The only time it seems to come up is for Unix file mode switches (chmod etc), which likely date to this time when octal was more common.

    Just some interesting cultural drift.

    1. SoftTalker · · focus · HN ↗
      Octal allowed used of simpler numeric displays (numeric nixie tubes or 7-segment displays) as you only needed digits and not ABCDEF that you'd need for hex notation.
      1. rswail · · focus · HN ↗
        Octal on a PDP-11 meant that the instruction set (16 bits) allowed two-register instructions with src/dst register and modes taking up 12 bits.

        So you programmed the front panel with 3 fingers for octal instead of 4 for hex.

Open on Hacker News to reply ↗

Unofficial Hacker News client; not affiliated with Y Combinator.