Computers, as I understand them
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Computers as I understand them

by Stuart P. Bentley


I'm not sure where I learned the stuff I'm going to write here. I think it started somewhere around Wikipedia, then spiralled off into perusing the Jargon File, sprinkled with some loose Googling into long-forgotten 1993 home pages and archived posts to mailing lists. Raymond Chen's blog, The Old New Thing, contributed a lot to my understanding of the history of Windows.

There's no real authority to any of this: I wasn't around for pretty much all of the stuff I'm going to write about. Most of this is me half-remembering things I read on the Internet somewhere and filling in the gaps with over-simplistic interpretations and assumptions that fit the narrative I've arbitrarily constructed.

Since I'm writing this as a text document on GitHub, if you read this and notice that I've got something rather wrong, you can suggest an edit by submitting a GitHub pull request, or just email me at:

This document is formatted as Markdown with footnote syntax.


Computers are more of a story than a science. Programming is less about understanding complex mathematical theories than it is about knowing why people made the weird decisions that shaped every interaction we have with computers to this day.

Chapter 1: Everything Before The Sixties

The first computers ever invented are generally agreed to be Charles Babbage's Difference Engine and Analytical Engine, mechanical devices designed around the 1840s. Lady Ada Lovelace (daughter of Lord Byron) wrote a sequence of operations that could be performed using the Analytical Engine, that would be the first computer program ever.

However, while Babbage's designs for the machines were complete by the time of Babbage's death in 1871, a working Difference Engine wouldn't be built until nearly a century later, and a completed, working Analytical Engine, as of June 2015, has never been built. As a result, the widespread influence of these particular machines that Babbage envisioned never materialized: when the first computers as we think of them were built around the time of World War II, their builders did it from scratch, with little to no awareness of how the Analytical Engine would have worked.

Here are the lessons of this story that are relevant today:

  1. The most detailed plans will never be more than a historical footnote if you can't carry them out.
  2. Just because something's possible with current technology, doesn't mean you should try it with current technology.
  3. Female programmers were here first.

The two most influential developments of the nineteenth century on modern computers would be much more pedestrian: the telegraph and the typewriter.

The Electric Telegraph

The notion of sending messages electrically had been in discussion since the eighteenth century, but ran into problems around the notion of long-distance transmission. You can't just string one wire the whole way for very long distances, since eventually the electric current can't make it from one end of the cable to another.

The Relay Switch

Relays are how this got fixed: you'd take from a new, locally-generated electric source, and then re-transmit the electrical state of your input by having that input magnetically pull the switch for the new electricity. (This ended up being really useful for building more complex electrical machines, prototyping the domain of solid-state electronics, but that's a whole separate topic from this current telegraph/typewriter narrative.)

Ultimately, practical implementations of electrical telegraphs didn't really start until about a century later.

Cooke and Wheatstone

The UK's Great Western Railway had one of the earliest electrical telegraphs, which started out using six parallel electrical cables, so as to make figuring out the letter being communicated "easy" by following a series of left/right branches. However, these six parallel cables ended up requiring a lot of maintenance, and as the cables would get damaged, the operators (who had quickly gotten used to which series of switches referred to which letters) would need to devise more complex codes using fewer switches.

Meanwhile, in America, Samuel Morse was devising a telegraph system that used a single line to transmit its messages, along with a specially-designed code.

Morse Code

An Appreciation for Binary/Digital

Punched Paper Tape

Baudot code

The Typewriter

Western Union

The Telephone

The pendulum swung back to an analog technology


The TeleType


Chapter 2: The Sixties