-=[ Butts, and the Internet ]=-
On domino effects, real and imagined
2019-10-23
## First... Butts
Let's talk about butts. Specifically horse butts.
There's a story that's been going around the Internet, probably since
its inception, about how the dimensions of spaceship parts are
indirectly derived from the width of a horse's butt. The short version
is something like this:
> Roman chariots were typically pulled by two horses. Therefore
> chariots were about two horse butts wide. When the Romans built stone
> roads, they put ruts in to keep the carriages aligned. They used the
> existing widths of ruts as a guideline for the stone ruts, and then
> carriages throughout Europe were built for those new stone ruts. Fast
> forward to the industrial age and you find that European railroad
> builders used the ruts in the stone carriageways as a guide for how
> wide to build the rails (i.e. the gauge). This meant a whole bunch of
> trains in Europe being built approximately two horse butts wide. When
> America started building railroads, European engineers were brought
> over and used the same measurements. A final fast forward to the space
> age, and you've got rocket boosters for the Space Shuttle being
> transported by rail through rail tunnels, and so they need to be skinny
> enough to fit through those tunnels.
There are some obvious problems with this. The United States didn't
have a common track gauge until after the Civil War, and it was only
chosen because it happened to be the only one used in the North. Even
more glaring here is the fact that train tunnels are quite a bit wider
than train tracks, and in fact were not an issue they had to design
around for the shuttle rocket boosters. Snopes does a great job of
tearing this one down. [1]
As it turns out, simple boring happenstance is the main reason these
things seem to line up as they do.
## CR+LF
Way back in the 1960s, the ISO and ANSI (then called ASA) were in the
process of standardizing character sets. Part of any set of printable
characters is a way to indicate that text needs to appear on a new
line. The two contenders were the `CR+LF` two-byte combo, versus a
single `LF` on its own. In C-like languages, these are represented as
`\r\n` and `\n` respectively. The ISO drafts suggested either `CR+LF`
or `LF`. The ASA draft only used `CR+LF`. Either way, a two character
sequence was supported by both standards in order to produce the new
line effect.
But why? Surely one character ought to do it. Indeed, in most use cases
today, we only use `LF`, so what was the need?
As it turns out, a lot of computing at the time was done using Teletype
Model 33 ASR machines as terminals for input and output. These machines
required both instructions in order to bring the printer head back to
the start of the line, using `CR` ("carriage return"), and down one
line, using `LF` ("line feed").
We no longer use Teletype machines, and haven't for some time. That
hasn't stopped the various twists and turns of history from keeping the
`CR+LF` alive, long after its original technical need had been
obsoleted.
When Unix arrived on the scene in the 1970s, it used the `LF` character
alone to denote a new line transitions in text files, taking the
shorter option in the ISO specification. Despite this efficiency, later
operating systems like MS-DOS and Windows preferred the `CR+LF` line
delimiter, adhering to both standards.
In 1989, the earliest version of the World Wide Web was born, and with
it, HTTP. Like any other text format, newlines needed to be
represented. From HTTP/0.9 straight through to HTTP/1.1, the `CR+LF`
was used to denote the end of an HTTP message, and in the case of later
versions to delimit headers. Part of the reason the two-character form
of newlines was used was the differences between operating system text
formats. HTTP/2 and HTTP/3 now use a compressed binary header format
that does not make use of of the `CR+LF` to delimit headers, but since
only about 41% of websites use HTTP/2 [2], and HTTP/3 isn't
standardized yet, you're still likely using `CR+LF` under the hood in
2019, regardless of which operating system you use.
Much like with horse butts, there's a cool story of how some obsolete
technology makes a surprise appearance in modern technology. Unlike the
horse butts, we don't need to squint in order to see it right there in
the technology we're using. In both cases, it's still a matter of
boring happenstance that caused an old weird technical decision to last
many years longer than it should.
(HTM) [1] https://www.snopes.com/fact-check/railroad-gauge-chariots/
(HTM) [2] https://w3techs.com/technologies/details/ce-http2/all/all