Magic Numbers
exple.tive.org
exple.tive.org
[1]: https://en.m.wikipedia.org/wiki/Asynchronous_Transfer_Mode
OTOH, skimming the Wikipedia article, it seems to me that overhead in that system was proportional to message length, so perhaps length of 53 bytes was still meaningfully better than 64 bytes.
Doesn't quite lock into the memory banks so easily.
Semi-related problem I dealt with recently: Google Cloud seems to choose a different magic number of 1460 for their VPCs default MTU, which is annoying if you don't know because its different than the default of everything else (such as docker) will cause random packet drops if you do a standard install of those tools.
Took me a few hours to figure this out.
Later I researched it, and they were blocking all of ICMP which not only killed ping, but messed with mtu path discovery. Found some information about it on a Cloudflare blog: https://blog.cloudflare.com/path-mtu-discovery-in-practice
[1] https://en.wikipedia.org/wiki/Standard-gauge_railway#Origins
That same admin had made cool menus and guide posts, documents that showed everyone about the net.
We had many system wide chats about stuff and everyone was all about helping everyone else.
Then we had the Eternal September... or was it December. In any case, for a couple years there before we got the first browser.
Everyone was mentored onto the Net in the early days. I wish that would have continued, but it would never have scaled, ah well.
Yes, I had a list of machines I could telnet to. Each offering some resource.
Oh, one cool thing was being able to ask for a bigger disk quota, download some big stuff and swing by the office to move it onto portable storage. SCSI disk or floppy or tape. I loved those chats right there in the server room!
I can totally understand that feeling, but my personal experience is honestly that "protecting the company from malicious employees" by technical means is often just window dressing.
A patient malicious internal actor that is both technically and socially competent can cause much more damage than most companies would ever admit to themselves (but those actors are rare enough to keep modern workplaces running just fine).
In short I think that just giving employees root access to some important company-internal system could work out surprisingly well even for decently-sized companies (not that I'm advocating for that :P).
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1. The VMS equivalent, to the best of my recollection, of rm -rf *
You could lower or raise the frame size and have it take any amount of microseconds you want. Perhaps ~4ms was selected with human interaction times in mind. You can send a frame, process for a few ms, then send one frame back quick enough for feedback to appear as instant.
If that's indeed the reasoning, then it's amazing how arbitrary decisions made in the past end up deciding today's standards.
Now I want the story of the 9000 bytes MTU.
* 2018: https://blog.dave.tf/post/jumbo-frames/
* April 2023: https://news.ycombinator.com/item?id=35647779
The 1500 byte frame size was introduced with 10 Mbit/s DIX Ethernet. PARC Ethernet had 8 bit terminal addresses whereas DIX Ethernet introduced 48 bit MAC addresses.
But something seems off in the calculation. 2^12 microseconds for one frame would be awfully slow. [EDIT: I stand corrected below]
> 12288 bits, which takes 2^12 microseconds to transmit at 3Mb/second,
A story that's passed around a million times whose truth content is damn close to nothing?
SRBs were made in Utah by Thiokol and sent by rail in sections. The limiting factor (choke point) was a single mountain tunnel, which was built a long time ago and was influenced by the winners of the rail gauge wars.
If you want to be confrontational skeptic to seem original, that's all you.
The tl;dr: the "limiting factor" is a tunnel width of 18', against a standard US loading gauge of 10'6", and a standard US track gauge of 4'8½" ... and the SRBs are 12' in diameter, which doesn't seem clearly limited by any of those factors whatsoever.
Am I missing something?
Pretty much every factual allegation in the original article is false, and to cap it all off, actually trying to track down the key assertion--the effect of rail transportation limitations [implied to be caused by history dating back to Roman times] on booster design--indicates to you that it had no relevance whatsoever.
Snopes is accurate in that the track gauge being slightly less than 5' is somewhat correlated with the width of two horses. But the track gauge being slightly less than 5' isn't even relevant to the main claim!
Let me give the actual answers to the questions:
> That's an exceedingly odd number [4'8½" track gauge]. Why was that gauge used?
Various railroad companies in the US over the 19th century moved to standardize gauges as the interconnected nature of railways meant that it was far more beneficial to have a uniform gauge throughout the system rather than dealing with constant gauge switches. The single biggest gauge conversion was the decision of railroads in the South to move to the same gauge as the Pennsylvania Railroad, 4'9", in 1886, converting some 11,000 miles of 5' gauge track to 4'9" in a weekend.
Yes, I said 4'9", not 4'8½". The difference between these two gauges is generally within tolerance, but higher speed traffic generally requires tighter attention to tolerances, and so setting the median at a world uniform 4'8½" standard gauge makes sense. Note that the British legislated the 4'8½" as that country's standard gauge in 1846.
> I see, but why did the English build them like that?
Well, there was a wide variety of gauges in England even after the passage of the Gauge Act, to say nothing of the time when the US was relying on English engineers to build railroads (which is the 1820s; by the mid-1830s, the US already has a pretty thriving homegrown rail industry). There's a broad cluster of track gauges around 5', and that's a pretty natural fit for a rail gauge.
> Well, why did they use that gauge in England?
Stephenson (who built the first practical steam locomotive) chose to use 4'8" for his early railways to match the existing (non-steam) railways then in use, and later expanded it to 4'8½" for the Liverpool & Manchester Railway for better curve engineering. Given the fact that Stephenson was one of the preeminent engineers in England at the time, there was a tendency to use his decisions as a basis for future railway design. However it should be noted that another great titan of English engineering, Isambard Kingdom Brunel, chose a 7' gauge for the Great Western Railway, and this prompted the gauge war that led to the passage of the Gauge Act.
> Okay! Why did their wagons use that odd wheel spacing?
At this point I have to seriously wonder... has this author ever seen a pre-industrial wagon? Because wagons don't have fixed wheel spacing! And they're not around 4'8½"; in fact, they're generally much larger. Look at a railroad car, and notice that it is basically a platform hoisted above the wheels. But wagons are generally built so that the platform is situated between the wheels, with relatively little clearance between the axle and the base of the platform.
> So who built these old rutted roads?
Not worth answering this question since we've deviated from any relevance whatsoever.
> And the ruts?
Going to comment on the answer here: "Roman war chariots." Dude, Romans didn't have war chariots; they became obsolete centuries before Rome existed.
> So, just what does this have to do with the exploration of space?
Absolutely nothing.
You see, the entire discussion I gave so far was on track gauge. But track gauge has no relevance whatsoever to the question of what the maximum size of a load you can carry on track is... that's loading gauge. And whereas track gauge is largely standardized across the world--4'8½"--the loading gauge is very much not. One should note that England, the birthplace of the railroad, generally suffers from extremely tiny loading gauges; the US is among the roomiest loading gauges in the world, especially Plate H double-stacked container traffic.
The main tunnel east of Ohio that's being referred to is likely Moffat Tunnel, which (per Wikipedia) has a width of 18'. Standard US loading gauge is 10'6" wide; the European standards are generally 10'4"; the UK can sometimes go down to 9' loading gauge. The Space Shuttle SRBs are, per Wikipedia, 12'... above all of them. So even the standard loading gauge in the US didn't limit the diameter of the SRB, much less any discussion of the track gauge!
https://discoveryparkofamerica.com/uncategorized/the-great-g...
No one is saying that the boosters are the same size as the rail gauge. Just the size of the train & train tunnels. As you mention, it’s not a standard size.
But the link and the intuition are the same. Our modern technology standards are based on anachronistic technologies. That was the point of the article.
No, they're not. The wheel ruts should be about 7' apart. The rail gauge is 4'8½", which is far less than that.
But as noted, if you trace the history of 4'8½", it comes from a 4'8" gauge (no longer perfect), and that comes from the existing infrastructure that was used to haul coal out of the mines, which came about in the 18th century, has no relevance to any wheel ruts whatsoever.
(Also, I should point out, there's also a tunnel-free route from Salt Lake City to Florida; just head north and over to Laramie instead of in the Moffat Tunnel. No clue what the actual route used was.)
Thanks for the details. If those coal mine gauges came from the dynamics of draft horses, would you agree with this example showing the idea that “anachronistic technology impacts modern standards?”
> If those coal mine gauges came from the dynamics of draft horses
I think coal mine haulage was dominated by hand, not by people (one of the reasons they used track technology--tracks make it easier to handle the heavier loads).
> would you agree with this example showing the idea that “anachronistic technology impacts modern standards?”
Not really. As noted, the track gauge wars occurred well into the development of steam technology (so the horse dimensions played no role), and it turns out for a variety of engineering reasons that the sweet spot for railroad track gauge is around 5'. So track gauges aren't based on anachronistic technology.
And also, as I pointed out, the track gauge didn't play a role in determining the size of loading gauge or tunnel width. And no one has actually ever provided any evidence that the people who designed the booster wanted a larger rocket, but couldn't build it because they were limited by the loading gauges. So it's not even clear that any concerns about the ability to transport by rail played a role in determining the size of the booster.
The only thing you have linking anything here to the size of the booster is this statement:
> The railroad from the factory runs through a tunnel in the mountains. The SRBs had to fit through that tunnel. The tunnel is slightly wider than a railroad track, and the railroad track is about as wide as two horses' behinds.
And every single fact in that statement is false: there is a path that doesn't run through a tunnel, so the SRBs don't have to fit through "that" tunnel; and tunnels are not "slightly wider" than railroad track, and railroad track is not "about as wide as two horses' behinds."
The answer is universally this: whoever designed <thing> at the time couldn't even fathom <modern thing>, and didn't need to fathom <modern thing> while they were designing <thing>. What they did at the time made perfect sense for the constraints they were aware of.
It’s also good to remind the next generation of engineers (and ourselves) to be humble because we stand on the shoulders of giants who they themselves stood on the shoulders of giants, and on and on
> I bet it seemed like a very reasonable tradeoff.
Also, it’s not very correct. You could dump bits straight into a memory buffer and still sanitize them before use. It’s not as insane of a security issue as presented. It’s more like downloading a file today and not executing it. It technically passed though your system memory, it was just never executed as instructions.
Well, I think it made the author feel good about themselves so maybe they didn’t notice it doesn’t serve a purpose to the reader. It happens a lot.