How did Raymond discover his carrier-screaming talent? And his homemade Marauder’s Map

George wonders, "I am curious how Raymond found about his talent. Maybe it will be an interesting post."

This isn't like a superhero who discovers as a young adult that he has powers beyond that of mortal men. And there was no radioactive spider. It was a simple case of problem-solving.

The basic way of checking whether the mainframe was up was to go into the lab and see if the terminals responded. But of course this meant having to hang around in the lab building all day.

The next way of checking whether the mainframe was up was to stay in your dorm room doing some other work while listening to a portable cassette recorder, and then every so often firing up your computer and trying to dial in. If the mainframe responded, you packed up your bag and headed to the lab. Otherwise, you stayed in your room and kept working. (I was one of the fancy kids with my own computer.)

It was a bit of a disruption to have to fire up my computer (or, if I was already using the computer to play a ga^W^W^Wwork hard on a paper, to save what I was doing, exit the program, and then fire up the terminal program), so I tried to fake it by screaming the carrier into the phone.

And once that worked, I realized I was no longer tied to my dorm room and could go about my regular business around campus, calling in every so often to see if the mainframe was up.

Why scream and not whistle? Because I can't whistle loud enough for the modem on the other end to hear me clearly.

"Wait a second, it was the answering modem's responsibility to send carrier first. Why did you need to say anything at all? Just listen for the answering carrier."

For some reason, the mainframe always sent answer carrier regardless of whether the system was up or not. To see if it was actually up, you had to send originator carrier, and then see if it responded with modulated tones. I have no idea why it worked that way, but I took advantage of it: I don't have perfect pitch, so having the answer tone as a reference let me generate my originator tone more accurately.

I later discovered that the mainframe also treated a certain DTMF tone as equivalent to originator carrier. (I don't remember which one. Didn't realize there would be a quiz twenty-five years later.) Therefore, if I was calling from a touch-tone phone, I could push the appropriate button instead of having to scream.

And in case you were looking for a demonstration, I'm afraid I will have to disappoint you. The passage of time has damaged by carrier-screaming ability. I can't quite get to a high-enough pitch any more.

Okay, so that wasn't an interesting post. To make up for it, here's something interesting:

There was a command on the mainframe to list all the users who were logged on, and one of the pieces of data that you got for each logged-on user was a four-digit hex value that everybody ignored. It took a while, but I eventually realized that the value was statically-assigned to each terminal.

Over the next several weeks, I visited as many computer terminals on campus as I could, including some really obscure ones, like the abandoned acoustic-coupler terminal on the second-and-a-half floor of the library, and collected the terminal IDs. Then I wrote a program that drew a map of every terminal room on campus with the name of the logged-on user printed in the appropriate location.

The upshot of this was that if I saw a friend online, I could usually tell exactly where they were. (If they were at a terminal ID assigned to a dial-up line, then I assumed they were in their dorm room.) Occasionally, they'd appear at a previously-unknown terminal ID, and I'd ask them where they were, so I could add it to my little collection.

In my third year, they redesigned the university network and terminal IDs were assigned dynamically, thereby rendering my program useless. But it was pretty awesome while it lasted. I could notice that a classmate was online and write, "Hey, I'll be right over. You going to be in the Physics Lab for a while?" And they'd be like, "How'd you know I was in the Physics Lab?"

Comments (14)
  1. Andrew says:

    I dreamt Raymond slept extra soundly last night.

  2. Rick C says:

    Good news–at some point the blog software was updated so that comment links work again!

  3. CmraLvr2 says:

    What baud rate do you scream?

    [Read the linked article. -Raymond]
  4. Adam Rosenfield says:

    @Rick C: In Firefox 25, comment links are still as broken as they have been for me for the last couple of years.  When you first open a linked comment, it doesn't scroll to the anchor since the comment hasn't loaded yet (they're loaded asynchronously).  But if you hit enter in the URL bar, it scrolls to the comment then.

    Internet Explorer 10 and Chrome 30 don't have this behavior — they both automatically scroll to the comment as soon as it finishes loading.  I don't know what (if anything) the HTML spec says about this, but I certainly prefer the IE/Chrome behavior.

  5. Pseudo-Anonymous says:

    Nitpick: "…my carrier screaming ability" not "…by carrier screaming ability"

    Andrew: Hilarious.

    On another side note, the comment links also work in IE11.

  6. Danilo Piazzalunga says:

    It certainly is an interesting post. Too bad bad your Marauder's Map only lasted for the first two books, er, years.

  7. db2 says:

    Oh how I wish I attended college during an era when a man might dial a pay-phone, scream into the mouthpiece, listen for a moment, hang up, and then resume normal activities.

  8. cheong00 says:

    On a related look regarding the terminal ID, since occasional I lend my hand to help reinstall the bootloader softwares in computer labs, I helped so many times so I actually remembered the IP ranges of individual PCs there.

    And then I was a campus BBS user, and like most IP based BBS it has the login IP address shown on the user info page if the user is login.

    There was one case that another BBS user who was my classmate needs help and I was in the affilated clubs' room of studuent union. I told him to wait and "I'll go and find you at room ST502" and he was amazed.

    On a not so related note of this post, after I acquired knowledge of how to write "expect" script to prevent idle kickouts, I kept login the BBS straight 2 years (expect downtime of both servers) through the UNIX clusters and they can't guess my actual location using that infomation, yet I can still find them with finger. :P

  9. T. West says:

    > "How'd you know I was in the Physics Lab?"

    Not so hi-tech, but I fondly remember working in my office when a friend visited.  My office shared a phone with someone who was many cubicles away, but while talking, I heard the faint ringing of the other cubicle.  Without even thinking, I put my hand over the phone, and two second later it rang and I picked it up.

    I didn't think anything of it until I noticed my friend staring at me open mouthed.  "How… how… how did you know it was going to ring?"  He was almost white.

    I shrugged, and said "After a few years here, you just get a sense when it's going to ring.  Nothing special."

    Sadly, and I've regretted it ever since, I could not keep a straight face the moment I finished the sentence.  I've had to live with my failure to pull that off for years now, as it would have been, just, perfect.

  10. Dave says:

    >"listening to a portable cassette recorder" […] "screaming the carrier into the phone".

    Maybe it's just me, but it seems like there's a fundamental disconnect at work here in terms of tools available vs. tools used.

  11. Ian Yates says:

    @Dave – the portable cassette recorder wasn't all that portable I imagine.  And to change tapes just to have carrier sounds would be annoying :)  But kudos for noticing the disconnect – I had overlooked it.

    [If you can scream carrier, what do you need a tape recorder for? -Raymond]
  12. Brian_EE says:

    Not exactly analogous to the marauder's map, but when I was in college we used a DEC VAX 6400 cluster. I once sat there and changed the group ACL properties of one of my files to every possible value and then checked the directory listing. I learned that the numeric group values were in Octal, and compiled a list of all numeric values and corresponding names. The campus system administrator wanted to know where I got the campus-wide ACL information after I showed him the list…

  13. Mike.Shawaluk says:

    This reminds me of a story that a friend of mine once told me. At the time, he was working for Bell Labs in Batavia IL, and he was trying to troubleshoot a problem where one of their dial-ups was crashing intermittently. At one point he manually dialed the number on his phone, and for some reason he decided to blow into the receiver. He was surprised when this reproduced the crash! (and he was later able to replicate the error predictably). His coworkers called this the "blowjob" test.

  14. Dr Tongue says:

    I regularly hypnotise and insert micro-tracking devices into my colleagues' bodies. I once thought tracking their location could be more easily done by exploiting their smart phones, but decided against it as that loses the personal touch (hypnosis, the insertion ritual, and subsequent recollection via posthypnotic suggestion to retrieve the device from their stool, clean it, and return it for recharging, reinsertion, and [imagined] reward).

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