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posted by martyb on Monday November 20, @11:02PM   Printer-friendly
from the good-question dept.

If you've ever had dialup internet service, or still do, or just know someone that does, you have probably heard terms like "56k modem". "56k" has become almost synonymous with dialup Internet access. But it's such an arbitrary number. It's not divisible by ten, it's not a power of two... so why was it chosen as the fastest dialup speed? For the answer, we will have to travel back in time quite a while.

Our visitors from Google should be warned that this is not a "stripped down" explanation; it is intended for relatively technical readers. But if you really want to know where this magic number comes from, you need to understand some of the technical background. As we shall see, "56k" was not just pulled out of a hat.

[...] Anyone that has ever used a dialup modem knows full well that they don't actually get to connect at that speed, though. And that their connection speed varies each time they dial in. There are two factors at work here.

The first is the FCC. If you are in the United States, the FCC places a restriction on the power output of devices connected to the phone network. The result is that you will never be able to connect at a speed faster than 53.3 kbit/s.

The second is the overall complexity of the phone network. 56 kbit/s (or 53.3 kbit/s) requires very good operating conditions, as it is really operating beyond the paramaters of what the phone network is required to be capable of. Operating at these speeds requires that there only be one ADC between the user and their ISP (which is not guaranteed to be true, but typically is), and that the copper wiring in the user's "local loop" have very good electrical properties. Part of the dialup process that is used to initiate a connection is an evaluation of the overall quality of the connection; if it is determined to be lacking, the modem will automatically drop down to a lower data rate.

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  • (Score: 3, Interesting) by Rich on Tuesday November 21, @01:31PM (10 children)

    by Rich (945) on Tuesday November 21, @01:31PM (#1333725) Journal

    Tape has higher bandwidth than phone. Seeing all the retro stuff, I've been wondering how much data one could store on an ordinary cassette tape, given a halfway decent recorder. My naive ballpark estimate would be equivalent to 8 kbaud with 6 bits per symbol (30dB dynamic range for a bit of resilience and framing) for each stereo channel, i.e. 96kbit/sec. However, comparing this to a V.34 modem, and a bandwidth*dynamic factor of at least four over phone, it might be closer to 2*4*33 = 264 kbit/s.

    Has anyone ever tried that or at least put some thoughts into it?

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  • (Score: 2) by ewk on Tuesday November 21, @01:55PM (1 child)

    by ewk (5923) on Tuesday November 21, @01:55PM (#1333727)

    "Tape has higher bandwidth than phone."

    But latency kinda sucks...

    I don't always react, but when I do, I do it on SoylentNews
    • (Score: 3, Funny) by drussell on Tuesday November 21, @03:10PM

      by drussell (2678) on Tuesday November 21, @03:10PM (#1333737) Journal

      The latency may be bad, but as the old saying goes, "never underestimate the bandwidth of a station wagon full of tapes hurtling down the highway!"

      What's the latest LTO tape hold, 6TB each?

      LTO Ultrium 7 6 TB rewritable data cartridge
      Data capacity: 6 TB native
      Data cartridge weight: 200 g (0.441 lb)

      So a ton of tapes is what, about 30 Petabytes traveling at, say 75 mph? ... ...

      Sure, the latency sucks, but the total bandwidth is pretty sweet! 😎

  • (Score: 2) by jman on Tuesday November 21, @05:13PM (4 children)

    by jman (6085) Subscriber Badge on Tuesday November 21, @05:13PM (#1333750) Homepage
    My VIC-20 held about 100K per side (assuming a 30-minute tape), but given how tiny those BASIC programs were, never needed more than a handful of tapes.

    After upgrading to the C64 and splurging on the floppy drive (actual 5-1/4", not those pretend not-really-floppy 3-1/2" things), total storage per media actually went down a little as it was only 170K (single sided, double-density), but oh so much faster than loading from tape!

    Many in the Enterprise world still use tape for archival.
    • (Score: 2) by drussell on Tuesday November 21, @07:29PM (3 children)

      by drussell (2678) on Tuesday November 21, @07:29PM (#1333775) Journal

      It's pretty bad when C64 floppy seemed fast for you at the time. :)

      It's the slowest floppy interface ever.

      SO painfully slow!!

      • (Score: 2) by jman on Wednesday November 22, @12:02PM (2 children)

        by jman (6085) Subscriber Badge on Wednesday November 22, @12:02PM (#1333853) Homepage
        Well, it *was* forty years ago; most computers were slower. The V20 chip (an NEC clone of Intel's 8088) I used to build a DAS machine in the latter 80's ran at a whopping 5Mhz, which just blew away the C64's 1.something from a six or so years earlier.

        Now I have an "aging" i9 clocking billions of cycles per second, and even interprative languages run pretty quickly on it, given enough memory.

        The floppy comment was that it way faster than loading from tape.
        • (Score: 2) by drussell on Thursday November 23, @04:37PM (1 child)

          by drussell (2678) on Thursday November 23, @04:37PM (#1333980) Journal

          Well, it *was* forty years ago; most computers were slower.

          No, they weren't. Not the floppy data transfer rate.
          The C64-style floppy interface was by FAR the slowest, it's not even close!

          Commodore 1541: 400 bytes/sec
          Commodore parallel IEEE (PET): 1,800 bytes/sec
          Atari 810: 2,400 bytes/sec
          Apple Disk ][: 15,000 bytes/sec
          IBM PC 360kB: 32,000 bytes/sec
          IBM AT 1.2MB: 64,000 bytes/sec

          The floppy comment was that it way faster than loading from tape.

          It wasn't really, though. If the tape you were loading used a tape fastloader like Turbo 250 instead of the slow (even for tape) stock 300 baud C64 protocol, you could get 540 bytes/sec from tape. This is significantly faster than the stock 1541 drive's transfer rate.

          Sure, you can do various types of fastloaders or custom firmware on the 1541 and some methods even managed to get as high as 10,000 bytes/sec (still only ⅔ the speed of a stock Apple Disk ][ !!), but Commodore's "home" line was the only crap where fastloaders ever really needed to be a thing, because their stock performance was so utterly abysmal.

          • (Score: 2) by jman on Friday November 24, @01:17PM

            by jman (6085) Subscriber Badge on Friday November 24, @01:17PM (#1334030) Homepage

            That was not my experience. Using the tape drive I had from the Vic-20, it would take, say, two and a half minutes to load a game. From the floppy, it was under a minute.

            Not going to argue about theoretical specs, just what I actually saw.

  • (Score: 2) by kazzie on Tuesday November 21, @07:15PM (1 child)

    by kazzie (5309) Subscriber Badge on Tuesday November 21, @07:15PM (#1333770)

    Some background reading about what was achievable back in the day: []

    • (Score: 2) by Rich on Wednesday November 22, @01:55AM

      by Rich (945) on Wednesday November 22, @01:55AM (#1333813) Journal

      I knew most were in the range of some easy sort of zero-crossing detection in the 2kHz range, resulting in about 2kbps, but with some amplitude sensing, that could easily be increased. Back in the days, there was the ZN427 ADC which would have been able to retrieve 6 bits at, say 10kHz. I was wondering if anyone ever tried such a thing (or any "higher" modulation methods).

  • (Score: 3, Interesting) by Unixnut on Tuesday November 21, @07:35PM

    by Unixnut (5779) on Tuesday November 21, @07:35PM (#1333778)

    Not sure about audio cassette tapes, but I remember in the 90s you could buy PC hardware that would interface to your VCR and store/retrieve data from it (using video tapes as slow tape backup), as video tapes had the helical scan recording and wider track allowing for higher data density making it feasible for data storage requirements at the time.

    You could store a decent amount on a tape (I think like a few GB) and tapes were relatively cheap (especially compared to "proper" tape backup systems). Once CD-recorders became mainstream though I think the concept died out (around the early 2000's) as recordable CD's had the benefit of being readable in any CD-ROM drive, rather than needing a VCR + assorted HW to restore, and were less bulky per MB stored.

    I myself have pondered that with the advance in computational power and compression/ECC algorithms, a modern implementation may well be able to store more data on such tapes (which now you can pretty much get for free, or cheap in bulk).