38

There's a slightly obscure, slang meaning in tech circles of the word "pegged" as it relates to a computer's CPU. When it is fully utilised for a duration (at least several seconds), you can say that "the CPU is pegged".

Does anyone know the history or etymology of this usage of "pegged"?

  • 1
    What does the term actually mean in the context you are asking about? – Erik Kowal Oct 14 '14 at 5:41
  • 17
    That's it, when this question is asked I'm an old man. – dotancohen Oct 14 '14 at 7:51
  • +1 - I've thought about asking a similar question, though I've heard it in different contexts, e.g., the VCO is pegged high or the output voltage is pegged low, meaning that something is broken and forcing operation at the edge of the range. For some of these electrical versions, if the pegged parameter is a voltage, the word railed can also be used (referring to power supply voltage rails). – Justin Oct 14 '14 at 14:01
  • 10
    Ever seen a mechanical volt meter? There are small pins at the minimum and maximum points on the scale to prevent the needle from going too far. "Pegged" is when the voltage is at the maximum for the scale. – Hot Licks Oct 14 '14 at 15:29
  • 1
    @dotancohen - I hear you. I got my first voltmeter (an Eico kit, IIRC) about 1960. – Hot Licks Oct 14 '14 at 15:35
84

Many analog gauges such as speedometers have a maximum marking which is technically not as high as you might be able to make the reading actually go. To prevent the indicator needle from going too far beyond that marking and possibly getting bent or otherwise damaged when it hits the casing, a small peg is placed at or slightly beyond the maximum marking. Thus, when you achieve the highest speed the gauge will show, you have "pegged the needle".

(Hitting the peg is not damaging in the way that hitting the casing would be because the peg is placed much closer to the base of the needle than the tip, so there is less torque being exerted, and the torque is usually on a thicker part of the needle.)

Here is an image of a gauge, with the peg circled in green. On this one you don't have to worry about needle damage, since the gauge is circular, but you wouldn't want to have it measuring a pressure of about 100 psi and only showing a reading of about 20 psi because it had wrapped around.

pressure gauge with peg circled in green

(Unfortunately the only other reference I can find on short notice is Urban Dictionary (sense 6).)

  • 2
    This term is common for speedometers, tachometers VU meters (audio) and probably many others, with or without the literal "peg". – TecBrat Oct 14 '14 at 14:47
  • 15
    The reason for the peg is not to prevent exceeding the maximum marking (the peg may in fact be located past the maximum marking), but to prevent the thin, fragile metal needle from hitting the meter case and getting bent. – Andrew Medico Oct 14 '14 at 16:28
  • 1
    @AndrewMedico Really? I'd have thought that hitting the peg would be just as bad as hitting the meter case. – David Richerby Oct 14 '14 at 16:56
  • 10
    The peg is usually very close to the pivot, so there is less torque (small radius) when the needle hits the peg vs. the end of the needle (full radius) hitting the case. – Andrew Medico Oct 14 '14 at 17:04
  • 3
    Also, the needled is hitting the peg edge-on, somewhere along the length of the needle, as opposed to the thinner, weaker tip of the needle hitting the curved (concave) surface of the housing, which would be much more likely to bend the tip of the needle or to cause the end of the needle to get wedged and stuck against the housing. Or if the needle was moving fast when it hit the housing, depending on dimensions and angles, it could even pop past the point of maximum friction ending up stuck on the wrong side of the housing. – Craig Oct 14 '14 at 21:52
1

I have seen an actual pegged meter in the EE Lab at the University of Wisconsin. When the meter is hit with a sudden extreme over voltage, the needle hits the peg hard enough that the needle wraps around the peg.

Why is there a peg on the face of the meter? Probably because the meter isn't accurate above the peg point.

  • hi paul, welcome to el&u. we welcome your contributions, but here your answer is better phrased as a comment to hellion's answer. that being said, you won't be able to comment on other people's questions until you earn a little rep, by asking or answering other questions. – Erich Apr 29 '15 at 13:23
1

There are a few reasons for a Peg to by placed on the face of an analog meter. 1) The devise was designed to measure a certain range accurately. A peg prevents rotation beyond the limit. 2) Some of these devices have a limit to how far the pointer can rotate before it would jam or damage the device. 3) Many analog meters have a spring connected to the pointer under the 'face'. a) Often this spring is designed to bring the pointer back to zero...and a peg may be placed there as well. Stretching the spring would render the device inaccurate. b) In some meters, the springs are calibrated for the device, with precise resistance. To prevent over-tightening (winding) or loosening (unwinding) of the spring, a peg is placed on the the face to stop the pointer from breaking or stretching the spring, which would either break the meter, or make it inaccurate. The point is, if something is 'pegged', it is maxed out, full throttle, needle to the pin, peddle to the metal, or Pegged out!

-2

Peg in the sense of restricted or constrained, 19th C:

1824 W. S. Landor Imaginary Conversation. II. i. 15 [Marvell] I will not be pegged down to any plot.

Peg in the sense of a fixed price:

1882 Pall Mall Gazette. 8 Apr., Arbitrarily raising prices against them—‘pegging prices up’, it is called.

Peg in the sense of toiling labouriously for a long period:

1805 J. Stagg Misc. Poems 132 I' th' meanteyme th' fiddlers changt an playt As hard as they cud peg.

All of these show that being stuck on the maximum level has had analogous uses for some time. The first two are by analogy of pegs used to fasten something, while the last is more obscure.

Tachometers and similar dial-based measures are from around the same time, though I don't know when they first had pegs to block overrun, but it certainly has led to people talking of dials being pegged in the twentieth century so it's there as a source too. Since at the time talking about a car or engine being pegged could both be referring to this or also in the earlier senses I give above, chances are it's actually a combination of both that led to it being used. That two different people might understand the word in the same way, albeit by different routes, would only make it more likely to become current.

  • Though these things are true, they are not the path which our language took to give "pegged" this meaning in electronics. – SevenSidedDie Oct 15 '14 at 2:04
  • @SevenSidedDie If it's none of those things, can you show which it is? – Jon Hanna Oct 15 '14 at 2:05
  • It's the current top answer. – SevenSidedDie Oct 15 '14 at 2:07
  • @SevenSidedDie that answer in fact mentions one of the senses I mention in mine. Are you sure that's the one you meant to link to? – Jon Hanna Oct 15 '14 at 9:23
-3

Hellion's answer is probably right. But my first guess was that the meaning was more along the lines of "the CPU isn't really doing that much useful work, but its usage rate is being arbitrarily reported as" 100% - akin to a pegged exchange rate. (I hear the phrase "pegged at 100%" as "prevented from dropping below 100%" rather than "prevented from exceeding 100%"...)

It would be interesting to have actual evidence either way.

  • 4
    The notion of a "pegged exchange rate" comes from the same analogue gauge concept, I'd wager. – Lightness Races in Orbit Oct 14 '14 at 14:12
  • 4
    "Probably right" and "my first guess was" are not indicators of a good answer on Stack Exchange. We want answers that are correct and, ideally, backed up by references, not people's guesses. – David Richerby Oct 14 '14 at 16:58
  • 1
    @DavidRicherby: ok, so how does it differ from Hellion's answer? No one here has any actual evidence that a given etymology is connected to the idiom in question. I'm just trying to be a bit more explicit about that fact. – Steve Bennett Oct 14 '14 at 20:54
  • 1
    Because without any actual evidence, I have no real reason to think that either Hellion's or my explanation is more likely. My gut says Hellion's is more plausible, but I know (like you) that gut instinct isn't worth that much - so I offer another plausible explanation. – Steve Bennett Oct 14 '14 at 22:16
  • 1
    @SteveBennett Many of us were there when this etymology was current and not mysterious. – SevenSidedDie Oct 15 '14 at 2:05
-7

The original meaning of the word peg is a small stake driven to the ground or onto a wall to hold something down, or an item used as mark.

The word is of Dutch and Germanic origin.

peg (n.) mid-15c., from Middle Dutch pegge "peg," a common Low German word (Low German pigge "peg," German Pegel "gauge rod, watermark," Middle Dutch pegel "little knob used as a mark," Dutch peil "gauge, watermark, standard"), of uncertain origin; perhaps from PIE *bak- "staff used as support" (see bacillus). To be a square peg in a round hole "be inappropriate for one's situation" is attested from 1836; to take someone down a peg is from 1580s, but the original literal sense is uncertain (most of the likely candidates are not attested until centuries later). Peg leg "wooden leg" attested from 1765.

Therefore, to ask the question

What is the origin of "peg down your expenditure"

would be akin to asking the difficult to answer question

What is the origin of "driving me crazy".

English is full of idiomatic usage, like any language.

The world of computer science itself has frequently borrowed and adapted such idiomatic usage.

  • Hard drive, floppy drive, flash drive
  • driver
  • software, firmware, vapourware

The commercial world first used the word

  • the Renminbi was pegged to the US dollar
  • the price of apples was pegged to $0.50 a pound

It is then by no accident that computer professionals would spontaneously say

  • the CPU performance was pegged
  • the CPU was pegged

Furthermore:

peg (v.) "fasten with or as if on a peg," 1590s, from peg (n.). Slang sense of "identify, classify" first recorded 1920. Related: Pegged; pegging.

  • 3
    The term (in the computer sense) comes from voltmeters and the like. And this sense goes back 50 years, at least. – Hot Licks Oct 14 '14 at 15:37
  • The term is a few hundred years old. – Blessed Geek Oct 14 '14 at 15:39
  • 9
    @BlessedGeek Your answer is missing the point. While a "peg" may have been a wooden cylindrical dowel for hundreds of years, the usage in question ("being pegged", meaning at the maximum/minimum) is a more modern construct, and as the correct answers have noted, is based on analog meters. – Digital Chris Oct 14 '14 at 18:57

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.