Talk:Microcode

From Wikipedia, the free encyclopedia

Contents

[edit] Critique of the article

I am a computer engineer, as was kind of confused also. This is really not a place for technical info I guess. —The preceding unsigned comment was added by 192.55.52.1 (talk • contribs) 13:37, 16 June 2004 (UTC)

if you two have sufficient technical know-how to criticize the article, why don't you amend it so that it is accurate? after all, is that not the point of a wikipedia?—The preceding unsigned comment was added by 4.10.174.115 (talk • contribs) 03:33, 17 November 2004 (UTC)

[edit] Microcode redirect

I came here to find out what microcode was. Microcode redirects to this article, which present WAY more info than I can follow...oerhaps someone who knows what they are can add an additional article on microcode specifically, so I can learn what it is?—The preceding unsigned comment was added by 24.68.241.212 (talk • contribs) 07:04, 5 September 2005 (UTC)

[edit] PDP-8 "microinstructions"

I disagree with the use of the PDP-8 as an example of vertical microcode. The use of the term "microinstruction" on the PDP-8 has an almost entirely different meaning that conventional microprogramming, but it is more akin to horizontal microprogramming than vertical, because it uses bitfields to control independent (though related) operations.

A better example of vertical vs. horizontal would be the HP 2100 vs. the IBM 360/65. The former has a very narrow (24-bit) microword, and is very vertical, while the latter has a very wide word (105 bits, IIRC) that has almost no encoding - most of the fields directly control individual hardware operations.

The use of the term "microinstruction" on the PDP-8 should perhaps be explained in its own section, with an explanation that the PDP-8 is not microcoded in the normal sense, but is hardwired and has an ISA that includes the "operate" instruction with fields for various operations. --Brouhaha 06:06, 10 September 2005 (UTC)

I understood that section to mean something different. I think it was trying to use the PDP-8 assembly language as a rough example of what "vertical microcode" is like. (I don't necessarily agree that PDP-8 assembly language is the best example).
On the other hand, you're correct that what the PDP-8 called "microinstructions" has very little to do with what we're talking about here and we might want to explicitly disclaim much relationship.
Atlant 23:34, 10 September 2005 (UTC)

[edit] Praise

Thanks this is a really good summery about microprogramming....if someone does not understand this and claims to be a computer engineer i recommend to switch your career.—The preceding unsigned comment was added by 142.150.27.42 (talk • contribs) 08:46, 31 October 2005 (UTC)

If someone types in the above and can't even spell 'summary' or 'I' then I recommend you switch off your computer and immediately stop wasting the planet's ecological system.
Note the above user was ostensibly accessing Wiki from the University of Toronto. Canada must therefore go back to the drawing boards if their students still can't spell or type. Sorry, Canada.] —The preceding unsigned comment was added by 62.1.163.85 (talk • contribs) .
62.1.163.85, be sure to read WP:NPA.
Atlant 22:30, 25 June 2006 (UTC)

[edit] Grave omission!?

I was quite simply flabbergasted when I noticed that this article does not at all mention the reprogrammability (flexibility, upgradability) reason for using microprogramming vs hardwiring. Correct me if I'm wrong, but isn't this reason as important as the emulation issue? --Wernher 23:15, 21 January 2006 (UTC)

But the article does mention this! See:
Microprogramming also reduced the cost of field changes to correct defects (bugs) in the processor; a bug could often be fixed by replacing a portion of the microprogram rather than by changes being made to hardware logic and wiring.
If you feel it needs more stress, this is Wikipedia so you know what to do: be bold!
Atlant 01:33, 22 January 2006 (UTC)

[edit] Work in progress

I stumbled across this article. As the above comments indicate, it definitely needs some work. I have some experience in this area, so will contribute what I can. Post any issues or questions here. Joema 02:07, 4 March 2006 (UTC)

The change to the VAX section is wrong. The first VAX, the VAX-11/780, did not use AMD 2901 bit slice components. I don't think any VAX did use those for the main CPU other than possibly the low-end 11/730 (and the electrically identical 11/725). --Brouhaha 06:18, 4 March 2006 (UTC)
Revised VLIW/RISC section. Added some items and removed "RISC as vertical microcode" sentence. This seems like a stretched comparison, not sure it's sufficiently close to warrant using. Discuss if any questions. Joema 18:45, 4 March 2006 (UTC)
Thought about it and restored RISC/vertical microcode comparison. Joema 19:01, 4 March 2006 (UTC)
Brouhaha, you're correct -- only Nebula/Low-Cost-Nebula (11/730, 11/725) used the AMD bit-slices. (We also used them in the PDP-11/34 and /44 Floating-Point Processors, but that's not at issue here.)
Atlant 17:51, 29 June 2006 (UTC)

[edit] Modern x86 processors

How does microprogram/microcode, specifically the VLIW/RISC section, compare to modern x86 CPU's? Like modern Pentium processors exposing a CISC instruction set but internally resembling more of a RISC processor? Fuzzbox, 29 June 2006

The following discussion is an archived debate of the proposal. Please do not modify it. Subsequent comments should be made in a new section on the talk page. No further edits should be made to this section.

The result of the debate was Move. —Wknight94 (talk) 02:24, 5 August 2006 (UTC)

[edit] Move to Microcode

This article is listed at Wikipedia:Requested moves to be moved to Microcode, with the rationale "Article states that "Microcode" is the more common term, and hence it should be the head." Please express your opinion below. —Centrx→talk • 04:25, 29 July 2006 (UTC)

  • don't move - microprogram is a more formal term for it, just as in the case of typical software 'program' is a more formal term than 'code'. The redirect from microcode is sufficient. --Brouhaha 05:39, 29 July 2006 (UTC)
    • I completely agree with Brouhaha. Microprogram is the formal term; Microcode is slang for that. This from 30 years experience in the industry, esp. with the big iron in IBM's stable. -R. 18:51, 31 July 2006 (UTC)
  • Strong Support. Microcode is what the technoligy is. It has been around since the 1950s or 1960s if not earlier. I could be biased here since I did program with/write microcode. Never heard the term microprgram when I was involved and I have never heard that before this discssion as anything other then a tiny program segment. Vegaswikian 19:29, 30 July 2006 (UTC)
    • You've led a sheltered life, then. Search on Amazon for books with "microcoding" in the title; then search for "microprogramming". There are eight times as many of the latter. The ACM and IEEE held conferences and workshops on "microprogramming"; they held none on "microcoding". When Maurice Wilkes invented the technique in 1951, he called it "microprogramming", not "microcoding". "Microcoding" is effectively a slang term for "microprogramming", just as "coding" is for "programming". The existence of a commonly-used term that is less formal justifies a redirect, but does not justify renaming the article. The article name is correct as it stands. --Brouhaha 00:50, 31 July 2006 (UTC)
  • Comment I always thought that microprograms were written in microcode, much like assembly programing is done in assembly language or assembly code. Seems simple to me. Atlant 19:12, 31 July 2006 (UTC)
  • Oppose moving it. When the concept first appeared, it was called control store, but its technological flowering came out of Cambridge University and was called microprogramming by its inventors, notably Maurice Wilkes. Microcode is the newer, less formal term. Microcode already redirects to it. If "Microcode" already existed and contained significant content, then merging might be worth arguing, but that's not the case. Moving it is a waste of time that doesn't improve the quality of Wikipedia - I've done pointless moves/renames in the past, and have come to realize it's a waste of time and effort. Rick Smith 19:55, 31 July 2006 (UTC)
    • Change vote to Strong Support - Okay, I just looked at the actual title of the article we're arguing about. The Google test shows the title microprogram is lost in the noise. Moreover, I was recently reminded that Maurice Wilkes, who coined the term microprogramming, has tried to enforce a very specific definition which excludes simpler forms of control store that he didn't invent. Those simpler forms are customarily referred to as microcode in the business, as are more sophisticated microprograms that incorporate Wilkes' innovations. To some extent, I wonder if we waste valuable intellectual resources arguing about things that redirect easily, but it seems to matter to someone who's willing to fiddle with the mechanics and make the change. In any case, I did a name change incorrectly early in my Wikipedia days, so this change in vote also indicates that I've developed a better understanding of the community naming policy. Rick Smith 15:09, 1 August 2006 (UTC)
  • Strong Support. The term microcode is much more commonly used. Just do a Google search on microcode vs microprogram. For many in the general public, their first exposure to the term was the Pulitzer-prize winning 1981 book The Soul of a New Machine, by Tracy Kidder: [1]. That book generally used the term microcode. During the RISC vs CISC debates of the 1980s, the term most often used was microcode (RISC processors aren't microcoded). Do a Google search on microcode + RISC vs microprogram + RISC. Microcode is much more commonly used. In general we should use the most common term, unless there is overwhelming reason otherwise. See Wikipedia:Naming conventions (common names). Joema 22:53, 31 July 2006 (UTC)
    • That's good rationale for having the redirect from microcode, but not for renaming the article. Having a more common name would be better if it was of comparable "correctness", but it is not. "Microcode" is a less formal name for the concept. As mentioned previously, computer architects (including the inventor of microprogramming), professional engineering societies, and computer science and engineering journal all predominantly refer to it as "microprogramming". In many fields there are more terms used professionally for which a less formal term is often substituted by laymen, and that justifies a redirect but not a rename. For instance, the Wikipedia article on "gerund" shouldn't be renamed to "verbal noun" even though the latter is more commonly used by laymen. The former is the precise formal term as used by linguists. For a technical term, it is appropriate (and perhaps an "overwhelming reason") to name articles for the precise technical term described, and simply mention and offer redirects from less precise terms.--Brouhaha 23:41, 31 July 2006 (UTC)
      • The WP guideline for naming articles is very clear: Name of articles "should be the most commonly used name". Microcode is much more commonly used than microprogram by the popular audience -- WP name guidelines emphasize that, not the most technically correct name as used by academic specialists. WP guidelines make exception if the "common name of a subject is misleading". That is not the case here. Joema 01:32, 1 August 2006 (UTC)
  • Don't Care: To me, the terms are interchangeable, perhaps a reflection of being a contractor who migrates from client to client who use different terminologies. As far as I know, I've never been misunderstood using the "other" term. As long as the typed word redirects to a relevant article, it doesn't matter which way it goes. —EncMstr 04:07, 2 August 2006 (UTC)
    • It matters because WP naming policy says use the most common name, and redirects are for less common usage. Thus you'd redirect from microprogram to microcode, not vice versa as now. Joema 17:14, 2 August 2006 (UTC)
The above discussion is preserved as an archive of the debate. Please do not modify it. Subsequent comments should be made in a new section on this talk page. No further edits should be made to this section.

[edit] Intel Core Microarchitecture

Needs more info on intel's recent advances in microarchitecture

Do those advances in microarchitecture have anything to do with microcode? (The fact that both words include the prefix "micro" does not indicate that microcode is involved in all aspects of microarchitecture.) If not, perhaps this question should be asked on the Intel Core Microarchitecture talk page, not the talk page for the microcode page. Guy Harris 06:35, 28 August 2006 (UTC)

[edit] some CPUs don't use microcode

The first few paragraphs seem to imply that *all* CPUs use microcode.

Towards the end, the "Microcode versus VLIW and RISC" section says that VLIW and RISC CPUs do not use microcode.

Confusing.

Then it claims that more recent "Modern implementations of CISC instruction sets" use microcode for only *some* instructions. (Is this a round-about method of talking about Intel Pentium processors, or is there some other "modern ... CISC"?)

I suspect this is incorrect.

My understanding is that, the instruction decoder on modern Pentium processors breaks down x86 instructions into one or more internal micro-ops, so it does have some similarities to the microcode store. But the information inside that decoder is technically not microcode, because the decoder is technically not a control store, because its output lines to not directly control the various parts of the Pentium CPU. Instead, the decoder output lines feed into the micro-op buffer, and as many micro-ops as possible (which varies cycle-by-cycle) are munched on each cycle (as selected by the superscalar dispatch unit).

Is it really true that some processors use microcode for some but not all instructions? --70.189.77.59 05:47, 15 October 2006 (UTC)

I've rewritten the first few paragraphs a bit in an attempt not to imply that all CPUs use microcode.
"Modern implementations of CISC instruction sets" is a way of talking about modern implementations of CISC instruction sets, including but not limited to recent Pentium processors; it also includes modern Intel x86 processors that don't have Pentium in their name, modern AMD x86 processors, and, I think, modern descendants of the System/360 processors (System/390 and z/Architecture).
In the case of S/390 and z/Architecture processors, most instructions are executed directly by hardware; others trap to what IBM calls "millicode", which consists of a combination of S/390 or z/Architecture instructions and special instructions executable only in a special "millicode" mode. See, for example, C. F. Webb and J. S. Liptay (1997). "A high-frequency custom CMOS S/390 microprocessor". IBM Journal of Research and Development 41 (4/5): 463-474. DOI:10.1147/rd.414.0463. ISSN 0018-8646. Retrieved on 2006-10-16.  That could be thought of as similar to PALcode on DEC Alpha processors.
In the case of P6 and later x86 processors from Intel, I have the impression that some instructions are directly translated to uops by the hardware, and other instructions cause a sequence of uops to be fetched from on-chip store; those sequences of uops could be thought of as microcode. They might not be horizontal microcode that directly controls gates in the processor, but not all microcode is horizontal.
In the case of the Nx586 and the AMD K6 and later x86 processors from AMD, I have the impression that they work similarly to the P6 and later Intel processors; at least in the Nx586 and K6, the internal operations are called "RISC86", suggesting that they're a RISC-like instruction set. They might also have some RISC86 code in on-chip store, functioning as a microcode equivalent for some of the more complex instructions. Guy Harris 08:26, 16 October 2006 (UTC)
Retrieved from "http://en.wikipedia.org../../../m/i/c/Talk%7EMicrocode_4176.html"