Talk:Bus (computing)

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bus width[edit]

Question about definition of bus width. Is it just the bandwidth of the bus times the duration of a CPU cycle? It would be nice if that were defined so I'd know for sure.

The "bus width" is the number of data bits that can be simultaneously transferred. Usually that is identical to the number of data wires in the bus -- i.e., the number of wires in the data bus. The memory bus to a typical memory chip includes 8 wires in the data bus, 15 wires in the address bus, and 3 wires in the control bus, giving a 8 bit bus width. The various serial buses transmit 1 bit at a time, so they have a bus width of 1 bit (no matter if they transmit that bit on a single-ended wire, or differentially on 2 wires, and no matter whether or not there are other control wires associated with it). -- 23:18, 11 November 2007 (UTC)

Erp Shubhy824 (talk) 19:33, 22 October 2016 (UTC)

article name[edit]

It's actually a more general term than computing. So this probably means moving. Or at least there needs to be another page, and have them linked together. Hmm. electrical bus perhaps? --drj

Do we really need separate articles for parallel bus, serial bus, internal bus, external bus? Can they be all covered here?

Any chance of some of Serial access, Serial transmission, Serial port merging?

"Buses" or "busses"? In American English at least, the former is the plural of "bus", while the latter is the third-person present tense of "to buss", meaning "to kiss".

Fowler says "buses" -- Tarquin


Is RS-232 a bus? Surely, it is not, it is strictly point-to-point and hence not a bus in any sense. The same goes for RS-422 and probably a few others too -- Egil

A bus should connect more than two elements. I agree that RS 232 is not reasonably a "bus" and is never described as such in the EIA standard (at least the Rev C that I have). I'm taking it out. --Wtshymanski 15:57, 15 Apr 2005 (UTC)

CAN bus[edit]

Hello! I'm a newbie here and as I didn't find anything in Wikipedia about the controller area network (CAN) bus, I intended to create its entry. But I'm not sure if I should add a link to it in the Computer bus page or in the Electrical bus page. What do you suggest?

By the way, to have an idea about what is the CAN bus, look at:

Thanks. -- Akira - Cleber Akira Nakandakare

An article about CAN (controller area network) is a very welcome contribution. It definitely think it should be listed on the Computer bus page, under Examples of External Computer Buses, Serial -- Egil 07:06 21 May 2003 (UTC)
done. -- 23:18, 11 November 2007 (UTC)


I think that the view of RS-232 not being a bus is conceptual, as someone else suggested about CAT5 nework connections. As a specific example, Centronics parallel connections are supposedly point-to-point, but parallel scanners and parallel ZIP drives (not to menion SCSI-via-parallel and IDE-via-parallel) have been out for years, which can daisy-chain between the computer and a printer. There are multiplexers available to run several independent signals over a serial connection; these are litle different from USB hubs and the like. Scott McNay 01:43, 2004 Feb 26 (UTC)

The PC-compatible world is full of stunts like that, but desparate work-arounds and expediencies in my opinion don't qualify the IBM PC parallel port as a "bus". It wasn't intended to be used as such, shucks, it wasn't even bidirectional till late in its evolution. --Wtshymanski 16:27, 15 Apr 2005 (UTC)


The following was on the main page in a hidden (html) comment: This is not a technical encyclopedia; this is a general-purpose encyclopedia. Thus, I think we should make an effort to make things understandable by non-techs, if possible, without sacrificing correctness or details. copied across and removed from article page by VampWillow 20:51, 12 Jun 2004 (UTC)

A diagram is in order. I'll put it on my to-do list unless someone beats me to it. --Wtshymanski 16:27, 15 Apr 2005 (UTC)

Asynchronous vs synchronous buses[edit]

The article says "All the equipment on the bus has to talk at the same speed, and thus shares a single clock." Surely this isn't true, since, for example the Motorola 68000 family implmeented asynchronous buses, where data transfer would vary in speed depending on how fast a peripheral chose to assert the "DTACK" (data transfer acknowledge) signal. --Wtshymanski 16:16, 15 Apr 2005 (UTC)

Spectra and Multics[edit]

RCA Spectra machines did not run Multics...multics was in the GE and the Honeywell camp. Spectra was a pseudo IBM compatible system running operating systems TOS, TDOS and TSOS. I suspect the comments about the BUS could be correct...but for Spectra machines of those that ran Multics?


I agree. But with either answer, it would probably not be the first such system. I don't know what the first would be, but I would guess that Burroughs D825 would be an early example. Perhaps this is too obscure to be illustrative. DHR 23:40, 19 February 2006 (UTC)

Three Bus Structure[edit]

Do you guys think it'd be worth mentioning the three-bus architecture? As I understand it, it's an important model and is used a lot in computer systems. I could write a little about it if it's a good idea. Haddock420 12:33, 13 January 2006 (UTC)

Yes, please write a little about it. -- 23:18, 11 November 2007 (UTC)

Yes, please write about it. Are you talking about the 3 buses in a system bus architecture, or some other three-bus architecture? --DavidCary (talk) 16:34, 11 March 2014 (UTC)

Article name[edit]

As nobody really calls the subject of this article a "computer bus" (do they?) I propose a name change, to "Bus (computing)" to fit in better with standard Wikipedia naming. Any comments? JulesH 09:50, 13 December 2006 (UTC)

I wholeheartedly agree - I was going to say exactly that. As nobody has responded within 5 days I'm renaming the page and setting the old name to be a redirect. I was going to edit all the links to here, but when I checked there were far too many for that to be viable. Perhaps a bot will sort that out later. Dan Pope 13:17, 18 January 2007 (UTC)

what is a another term for a computer bus? — Preceding unsigned comment added by (talk)

Is there a significant difference between a computer bus and a expansion bus? If not, both terms should redirect to the same article, with the difference (if any) explained in the article. --DavidCary (talk) 14:31, 18 July 2013 (UTC)

Ah, it seems expansion bus redirects to expansion card, which is somewhat a different topic. This topic is the architectural concept, which might be implemented in a number of different physical ways. One common way is to have cards that plug in, often some time after the other parts of the computer are assembled, which is what that article describes. There are many other computer buses that are not interfaces to plug-in cards; now days they are often even within the integrated circuit itself, so would only be visible under a microscope, and are fabricated when the integrated circuit is. Perhaps this could be explained better in these articles? W Nowicki (talk) 16:38, 18 July 2013 (UTC)

Is Bus an Acronym?[edit]

is bus an acronym?.. if so what is the full form?... —Preceding unsigned comment added by (talkcontribs) 13:00, 13 July 2007

I think it's important to clarify this one, particularly with references. Some people say it's short for Omnibus (latin for "for all"), wiki is the only source I've come across that mentions Bi-directional Universal Switch. I'll make it a project of mine for the next few days to find a source either proving or disproving it's acronym-ness. Alex Williams 23:51, 7 November 2007 (UTC)

I don't think that the bus we are talking of here is an acronym. Here is a list of bus acronyms which possibly do not suit the article here.
--Ahsasin8 16:40, 26 December 2007 (UTC)

I'm pretty sure that bus is not an acronym in this context, it's just an accessible metaphor for a transfer mechanism (like a motor bus). I think we need to remove the statement unless someone can come up with a credible citation. (talk) 14:01, 9 January 2013 (UTC)

I'd also like to add that my suspicion that "binary unit system" is a backronym arises from the fact that, as an IT professional, it just doesn't make any sense here. It's not a system of binary units or for binary units. Ultimately the information it transmits is binary, but you could say that of pretty much any computing resource. (talk) —Preceding undated comment added 14:07, 9 January 2013 (UTC)

Bus speeds for different devices[edit]

Some processors, such as the 68000, have provision for slow devices on the memory/IO bus and have a line (DTAK, for "data transfer acknowledge") which the peripheral will assert to signify it's had enough time to read/write the bus. So it's not strictly true that increasing bus speeds required increasing peripheral speeds, at least in the case of asynchronous bus designs. The whole world isn't an IBM PC, you know...or even an S100, for that matter. --Wtshymanski 18:53, 9 November 2007 (UTC)

PCI Express Bus Photo[edit]

The photograph nearest the top of the page states that the image is of a PCI Express bus... however the PCI Express article states that the PCI Express standard does not use a traditional bus, it uses lanes instead. -- (talk) 05:16, 6 December 2007 (UTC)

Yes, but that's just on the electrical level. All the pins from different lanes are still arranged in a single strip. Hence why the connectors differ in size: they have a different number of lanes each. -- intgr [talk] 17:33, 6 December 2007 (UTC)

PCI Express is not a bus, neither is RS-232 —Preceding unsigned comment added by (talk) 21:25, 8 June 2008 (UTC)

AGP after PCI?[edit]

Didnt AGP come before PCI?


I think the whole organization of "bus" articles related to data buses needs to be re-vamped. The way I think about it, a computing bus as described in this article is just a specific case of a data bus. For that matter, there is a whole family of data buses not addressed: those used to connect special-purpose computers in aircraft, cars, and probably lots of other applications. For example, RS-422, RS-485, ARINC 429, MIL-STD-1553, and CAN, to name a few. By the way, the term bus in my experience is commonly used to describe point-to-point (two device) communication networks. I would like to see a citation for the "must connect more than two devices" assertion. —Preceding unsigned comment added by (talk) 05:13, 9 February 2008 (UTC)

Data bus redirect?[edit]

Why does data bus redirect here? They are entirely separate things. You to combine a data, address and control bus (or multiplex them all) to make a bus that is described in this article. Rilak (talk) 11:12, 13 April 2008 (UTC)

I agree with this, although I'm not sure if a control bus is necessary in every bus. However there is a worse terminology problem here which is the circularity of the definition; if we say "A bus is composed of a data bus, an address bus and a control bus," it still leaves the question, "What is a bus?" If allowable by quotation guidelines, I'd recommend quoting the definition here: (I found that definition the most helpful in clearing this word up; I'm unaffiliated with that site.) (talk) 23:27, 10 June 2016 (UTC)

Contradiction and apparent attempt to exclude HyperTransport[edit]

The article's lead explicitly rules out point-to-point links as being a "bus". Yet that is what HyperTransport is, and it's listed as a bus further down in the article. Furthermore, I think this is mostly semantics. You can add a discussion about the strictness (or lack thereof) for the dictionary definition of "bus", or even "not a bus", but by and large the common usage is that "bus" refers to whatever connects the various components of a computer together and vice versa (nobody actually calls HT a "point to point link" except in formal papers). If anyone objects to this and cannot reconcile it with a separate paragraph about the meaning of "bus", please discuss further. Ham Pastrami (talk) 04:38, 21 February 2009 (UTC)

IEEE Std. 100 says a bus in the context of a microcomputer system connects "a number of devices" - that is, more than two. I don't think it's useful or appropriate to describe a point to point link as a "bus" since a bus implies that multiple devices can connect to it. I'm all in favor of common useage defining usage but not at the cost of ambiguity. Otherwise the word "bus" is meaningless. --Wtshymanski (talk) 15:36, 21 February 2009 (UTC)
A "number" is not "more than two", unless you are referring to another normative definition. The dictionary[1] provides: (1b) an indefinite usually large total and (3) a distinction of word form to denote reference to one or more than one. The 1b definition rules out point-to-point links and traditional buses equally; neither kind of bus is typically built for a "usually large" number of devices. In practice, there are also several high-profile precedents: front side bus and back side bus connect only 2 devices, unless you also want to count the clock; the "AGP bus" would also be a misnomer. Again, the article as-is mentions HyperTransport in several places anyhow (really, as it should) and using a conflicting, interpreted definition (correct me if I'm wrong, but IEEE does not actually say "Point-to-point is not a bus") is what leads to ambiguity. You have the lead and the body claiming different things. Also, I'm not at all sure what is meant by the word "bus" becoming meaningless. Aside from that one sentence, the article provides a solid background on what a computing bus is. It's not like this creates the ability for someone to add "a computer bus is a monkey". Please keep in mind that Wikipedia is not a technical manual (see point 5 especially), and things like IEEE or dictionary definitions are not necessarily appropriate to define the scope of an article. Ham Pastrami (talk) 07:48, 27 February 2009 (UTC)
Why does the IEEE definition not then say "two or more" instead of "a number"? That would be clear and would have shown an intent by the IEEE to include point-to-point links. Dictionaries often don't define things by exclusion because dictionaries (unlike Wikipedia) have to worry about space. A point-to-point link and a bus have significantly different properties - bus contention doesn't exist in a point to point link, for example. ( Recall all those desparate stunts in the 5 1/4 disk days for "networking" a classroom using nothing but the RS 232 ports and a bunch of diodes, pull up resistors, clever software, and optimism. RS 232 is not a bus and will bite the hand of anyone who treats it like one.) What is the difference between a point to point link and a bus? If they are synonymous, why are their two different terms? Personal computer users have long taken the Humpty Dumpty attitude towards words and definitions, starting with the murky idea of "formatting" a hard drive. I'm of the opinion that our technical vocabulary is the poorer for this practice. --Wtshymanski (talk) 14:59, 27 February 2009 (UTC)
Perhaps the IEEE definition is intentionally vague for the express purpose of not locking down the concept to specific electrical implementations? Again, if you want to make a more specific distinction between the general idea of a bus and the difference between traditional and point-to-point, you can, you just need to be more clear that there is a wider context and not narrow the article's purported scope. Within its common English usage, the difference between a point-to-point link and a "bus" is the same between an apple and a fruit. One is a specific type of the other. Ham Pastrami (talk) 16:41, 27 February 2009 (UTC)

BS detected[edit]

"Almost always, there was one bus for memory, and another for peripherals"

This is a contradiction with text later in the article and also false. While a separate I/O space existed on Intel processors, this is only true for them and derived CPUs such as the Zilog Z80. On the other hand, Motorola processors, MOS CPUs etc. mapped hardware registers in the same memory space with RAM and ROM. They were accessed using the same instructions and only one data bus existed on the majority of 1980s computers. -- (talk) 11:17, 18 April 2010 (UTC)

(replying two years late...) No, this is not false. The statement is discussing much older systems, the mainframes and minicomputers of the 1950s and 1960s. These generally had completely separate memory and I/O buses. Digital's PDP-11 of 1969 was one of the first systems to unify memory and I/O into a single bus. --Colin Douglas Howell (talk) 00:48, 21 August 2012 (UTC)

Further disambiguation needed[edit]

As a non-anglophone, I occasionally need to browse throu various pages to understand a voice.
In this voice the case was:
"Early computer buses were literally parallel electrical buses with multiple connections".
I clicked on "electrical buses " to understand the sentence, but I was redirect to the electric coaches, wich I think is not what ment here...
Any help?

Thanks & regards,
Michele, Italy. (talk) 16:24, 15 March 2011 (UTC)

Thanks a lot to user OlEnglish who updated the page


In computer architecture, a bus is a subsystem that transfers data between components inside a computer, or between computers.

What about comp-flashdrive? Josh, linguist (talk) 14:46, 10 March 2013 (UTC)

I think of a USB keyboard as part of the computer when it is plugged into a desktop computer's USB port.
Likewise I think of a USB flash drive as part of the computer when it is plugged into a desktop computer's USB port.
In these two cases, the USB bus "transfers data between components inside a computer", even though the keyboard and the flashdrive are outside the computer case.
Josh, linguist, can you help us Wikipedia: Make technical articles understandable by editing this to use easier-to-understand English?
Is there a better way of saying the bus transfers data between parts of a computer, even when some of those parts are outside the computer case, without going into a lot of technical caveats in the first sentence of the article?
--DavidCary (talk) 14:13, 5 June 2016 (UTC)
I think what you just said is fine, David: "The bus transfers data between parts of a computer." But I'm surprised that nowhere in the article is it mentioned that a bus can transfer data between more than two parts at a time. The definition I found here: was the most helpful for actually grasping the word "bus" itself. I understand this is an encyclopedic article, not a dictionary; however it should start with a clear and precise definition of the subject being discussed. (talk) 23:20, 10 June 2016 (UTC)