[Bloat] Re: [Cake] [ih] Bandwidth v Capacity [Early Internet Report when Vint was at Stanford (and DARPA PI)]

[Sebastian Moeller <moeller0@gmx.de>]

Mmmh, from the meta-peanut gallery

a) The man's name was Heinrich Hertz, and so the unit's name is hertz as well, not herz. Typically I would just silently correcting this internally when reading a text and not bother, but when a text is trying to show how to correctly name things, it should lead by example.

b) Just to be contrarian, how about using "data rate" or "information rate" when talking about what is achieved, capacity being the achievable limit of said rate and bandwidth being the spectrum allotted (I know, too easy)?

c) That ship has sailed, language is adaptable and typically dies not ask permission when changing connotations and usage/meaning. 

d) Not that it matters, I agree that bandwidth and capacity should not be confused (but see c) ) or we end up with bangers like:
	"out of a bandwidth of X Hz our modulation and encoding scheme allows a total bandwidth of Y Bits/second out of which a bandwidth of Z Bis/seconds were achieved in real world testing."

Re


> On May 31, 2026, at 13:49, Frantisek Borsik <frantisek.borsik@gmail.com> wrote:
> 
> Forwarding for visibility - a great "rant" on the usage of "bandwidth" vs
> "capacity", from Brian E. Carpenter https://profiles.auckland.ac.nz/bcar071
> 
> To read more, from people like Vint Cerf or John Day, on this topic, take a
> look into the archive:
> https://elists.isoc.org/pipermail/internet-history/2026-May/thread.html#start
> 
> All the best,
> 
> Frank
> 
> Frantisek (Frank) Borsik
> 
> 
> *In loving memory of Dave Täht: *1965-2025
> 
> https://libreqos.io/2025/04/01/in-loving-memory-of-dave/
> 
> 
> https://www.linkedin.com/in/frantisekborsik
> 
> Signal, Telegram, WhatsApp: +421919416714
> 
> iMessage, mobile: +420775230885
> 
> Skype: casioa5302ca
> 
> frantisek.borsik@gmail.com
> 
> 
> ---------- Forwarded message ---------
> From: Brian E Carpenter via Internet-history <
> internet-history@elists.isoc.org>
> Date: Sat, May 30, 2026 at 11:55 PM
> Subject: [ih] Bandwidth v Capacity [Early Internet Report when Vint was at
> Stanford (and DARPA PI)]
> To: Internet History <internet-history@elists.isoc.org>
> 
> 
> Hi,
> 
> Yes, that's a very nice slice of history. It leads me to one of my hobby
> horses: when did the solecism of using "bandwidth" to mean "capacity" first
> arise? This is something that should annoy every physicist, or anyone who
> has read Shannon's foundational paper [1]. Unfortunately, it's become
> firmly established in the Internet community and beyond. And it matters
> because it quite often creates confusion, particularly in media reports.
> 
> * Bandwidth is measured in herz (cycles per second) and is the frequency
> range that a communication channel can transmit.
> 
> * Capacity is measured in bits per second and is the amount of binary
> information that a communication channel can transmit.
> 
> There is no fixed relationship between the two (which is more or less the
> main point of Shannon's paper). Anyone who ever heard the startup screeches
> of a modem should know this.
> 
> To illustrate the issue, page 1 of Vint's report says:
> 
> "During the months of December (1975) and January (1976), we undertook
> extensive and detailed timing measurements of the ELF VDH behavior to
> ascertain the degree to which VDH performance affected total TCP
> bandwidth and delay."
> 
> That (and the other 14 occurrences of "bandwidth") should be "capacity."
> 
> Page 8 says:
> 
> "The actual
> line utilization is about 20% in each direction, assuming a nominal 50
> kbits/second available full-duplex capacity between ELF and the IMP."
> 
> That's correct usage.
> 
> My favourite sentence is on page 45:
> 
> "Many of the experiments have been
> frustrating, owing to a bug of some kind in UCL's buffer allocation scheme
> causing them to crash irrevocably when attempting to achieve high
> bandwidth."
> 
> If only they had tried to achieve high capacity!
> 
> So, my question is: when did this inaccurate use of "bandwidth" to mean
> "capacity" first arise? It was clearly well established by 1975.
> 
> I looked in Donald Davies's book [2], and it only uses "capacity" (I would
> expect no less of him). Baran in 1964 [3] used "capacity" correctly many
> times. He also used "bandwidth" correctly once [5] and debatably a second
> time [6].
> 
> Pierce [4] in 1961 was completely clear on the difference between bandwidth
> and capacity (and he learned directly from Shannon).
> 
> Regards/Ngā mihi
>    Brian Carpenter
> 
> [1] C. E. Shannon, "Communication in the Presence of Noise," Proceedings of
> the IRE, vol. 37, no. 1, pp. 10-21, Jan. 1949
> [2] D. W. Davies, D. L. A. Barber, W. L. Price & C. M. Solomonides,
> "Computer Networks and their Protocols," Wiley, 1979
> [3] P. Baran, "On Distributed Communications Networks," IEEE Transactions
> on Communication Systems, Vol. 12 No. 1, 1964, pp. 1-9
> [4] J. R. Pierce, "Symbols, Signals and Noise," Harper, 1961
> 
> [5] "In a conventional circuit-switched system each of the
> tandem links requires matched transmission bandwidths.
> In order to make fullest use of a digital link, the post-
> error-removal data rate would have to vary, as it is a
> function of noise level."
> 
> [6] "Most importantly, standardized data blocks permit
> many simultaneous users, each with widely different band-
> width requirements to economically share a broad-band
> network made up of varied data rate links."
> 
> On 30-May-26 15:13, Barbara Denny via Internet-history wrote:
>> While poking around on DTIC,  I found this interesting early report on
> the Internet while Vint was still at Stanford and Jon Postel was still at
> SRI (How many of you knew that? :-))The period of performance is Nov
> 15,1975 to Feb 15 1976.
>> https://apps.dtic.mil/sti/tr/pdf/ADA024823.pdf
>> You can find a little bit more info by using the contract number in dtic.
>> Happy Reading,barbara
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