Talk:Intel 80486

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This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL.

can you come on internet and surf well with a 80486 computer?

A 50mhz 486 or faster with 16mb of ram is suitable for surfing the internet. Just you'll need to use a lightweight browser, as most browsers such as Internet Explorer and Mozilla are very bloated. K-Melon and Netscape 3.04 come to mind. A software modem would also be a no-no.
The internet is usable on a 486SX/25 (the slowest 486 ever made) running Linux and the Dillo browser. However, a lot of web pages can't be accessed (such as Hotmail and Yahoo web mail accounts), and others look strange in this browser. Samboy 04:16, 23 Apr 2005 (UTC)

Curio: why is the "Intel Overdrive" specified as being a DX2? There were numerous Intel Overdrives, not all of them were DX2s.

It shouldn't be. The "Overdrive" 486 chips were available in both DX/2 and DX/4 form.

WHat socket did the 486 use? --Tarquin 15:38 Apr 28, 2003 (UTC)

A few different ones, Tarquin. Cris Hare is the best source for this stuff. Tannin

Regarding the new image of two SX 486 chips, could it be moved to the Intel 80486SX article? It is just that SX chips were not 'normal' 486s, and putting them in this article is analogious to placing a picture of a Celeron at the front of an article about the Pentium 4. Also (a tip), images this wide should be put below the first piece of text because people on lower resolution screens (such as the 800x600 I'm on at the moment) will see an image taking up all the screenspace above the first text of the article. Crusadeonilliteracy 16:08, 26 Nov 2003 (UTC)

I thought Intel always referred to this chip as the i486, never the 80486. I could be wrong. --Furrykef 06:39, 24 May 2004 (UTC)

I believe title "80486" is incorrect. 386 was officially "80386", but in 486 Intel dropped 80-prefix, and in Pentium numbers altogether. See pictures of prosessors, name "Intel i486" is printed on them, nothing says "80486". -- Mikko Paananen 14:28, 12 Jun 2004 (UTC)
I concur. 80486 was still a common layman's designation. The article should be renamed to Intel i486 and a redirect added from 80486. -- Jherico 00:55, 26 May 2005 (UTC)
You shouldn't confuse the technical identifier i.e., the chip product ID 80486 with the shorter (simpler, nicer) names used for marketing or by mere users like i486, 486. Also many terms used nowadays (like x86, it was either IA-32, i386 or 80x86) were never used at that time. --195.62.99.203 04:00, 15 Jun 2005 (UTC)
Here's a little bit of proof "http://logout.sh.cvut.cz/~astro/pictures/trade/a80486sx25.jpg". In case that link doesn't work, just use Google's image search for "80486". You'll see that at least some models of Intel (but also AMD) have 80486 printed on it. --195.62.99.203 04:06, 15 Jun 2005 (UTC)
By the way, you can clearly read "80486" on the photo at the top of the article. --195.62.99.203 04:53, 19 Jun 2005 (UTC)

Contents

[edit] Clock Multiplier

I think I don't quite understand that clock multiplier thing. Could you, please, explain it using eg. 486 DX4 processor @ 100 MHz? does it mean that processor runs @ 100 MHz, while system bus is clocked @ 33MHz, ie. three times less?

--89.102.25.151 17:30, 5 June 2006 (UTC)

Yes, a 100 MHz Intel DX4 uses a 3x multi on a 33 MHz bus. It's a clock tripled CPU. A DX2 50 runs on a 25 MHz bus. A AMD 5x86 133MHz is actually a 486 with a 4X multiplier on a 33 MHz bus (lots of people put the bus at 40 MHz and get a 160 MHz 486!) --Swaaye 18:32, 5 June 2006 (UTC)

[edit] DX2/DX3/DX4

Regarding the comment "DX4 runs at triple the clock speed because DX3 (supposed to run at 2.5x the clock speed) never hit the market".. This is conjecture, and is absolutely false.

The reason the DX4 was called such was due to the lawsuit in the mid 90s that decided that Intel could not use a number as a trademarked name. They could not call their chips "486" anymore; this is why they called it "DX4". "DX" for their naming system that had been in use, and "4" as a reference to the 486.

You'll note that 486 DX4 chips are not called "486" at all anywhere in Intel literature or on the packaging. They are simply called "Intel DX4". The 4x/3x multiplier "confusion" is because of Intel's use of "DX2" for their clock-doubled processors. Although Intel's intent at the time with "DX2" was to use it as a suffix that denoted a doubled clock speed, the use of "DX4" cannot be compared as such.

Intel never planned to release a "DX3", and there were no 2.5x 486-based chips from Intel.

What does "dx" stand for?

My own hunch is that DX, SX etc don't stand for anything. They're like the SL, SR, RX, LX letters used to name cars. The X looks futuristic and distinctive, and it sounds snappy when you say it. D has one syllable. Neither DX nor SX are a word. Other combinations of letters might have been undesirable - EX would have people calling it the "486-ecks", FX looks rude, WX is a mouthful to say, AX is "axe", and so on. Lupine Proletariat 15:09, 18 May 2006 (UTC)
Both these theories sound possible. However neither is sourced... Nil Einne 15:17, 3 July 2006 (UTC)

More on DX3/DX4

I was the original commenter objecting to idea that the "DX3" was reserved for a "2.5x multiplier". Although there are references to this fact (which I believe is false) on the web, I recall specifically by reading news articles at the time that the name "DX4" was chosen because of the "DX" tag already being used on chips and "4" being added to it to keep the name in line with their 4th generation (486) chips, after lawsuits decided that Intel could not copyright a number, as stated in the article. Also note that the clock-tripled DX4 is simply called the "Intel DX4", which leaves more credence to the fact of not being able / wanting to use the "486" name anymore. Additionally, the "4" in DX4 does make some sense as a name, whereas the "3" meaning 2.5x makes none. A good explanation of this (and agreement with this thesis) can be seen at Karbosguide, a PC reference site which pre-dates Wikipedia and the other articles claiming "DX3=2.5x" nomenclature on the web. To wit: (Note, the site's author, Michael B. Karbo, is not a native english speaker, and the site is translated by staff - hence the grammar errors. This does not detract from Mr. Karbo's extensive PC experience.)

"Contrary to what you might think, the DX4 were not named for a quadrupling. They were named this way because of the registry of Intel's 80486 and 80586 names. The DX4 name is separated from that context, so it could be patented. If DX3 referred to a tripling, this would not work. The same type of problem caused the next generation chip to be named Pentium, rather than 80586." Tcp100 06:12, 3 August 2006 (UTC)

[edit] WP bit in cr0

I think it ought to be mentioned that the 386 had a design flaw in its paging system. It did not enforce write protection at CPL 0. This makes it very inconvenient to implement copy-on-write in 386-compatible operating systems, because the kernel could not simply access user memory directly expecting an exception if a page were copy-on-write. Modern Windows NT in particular wouldn't be able to handle this.

The 486 solves this by enforcing write protection at CPL 0. However, to remain compatible with the 386, it has to be disabled by default. Bit 16 of cr0 was defined as the WP bit, enabling this feature.

The other big feature of the 486 from a systems programming perspective was the addition of important atomic primitives: cmpxchg (really cemented by Pentium's cmpxchg8b), xadd, bt, bts, btr. cmpxchg in particular, because all atomic primitives can be implemented based on it. (These need "lock" to be atomic; don't use them in non-atomic situations because they're slow.)

bswap turned out to be nice for the SHA hash functions but clearly wasn't an important improvement.

-- Myria 10:09, 9 August 2006 (UTC)

[edit] 486SL -- DX not SX

From memory, I seem to remember that the 486SL was a variant of the 486DX rather than the 486SX as noted in this article. We had a Zenith Data Systems 486-SL25 notebook (4MB RAM, 25MHz CPU) back in 1993-4. According to http://everything2.org/?node=486sl, it is a variant of the -DX chip as well. Is this article a suitable source, or do we need to find a better one?

--193.120.178.201 15:56, 10 August 2006 (UTC)

[edit] Dates?

When was the 486 introduced?

-- It was introduced in 1989, became obsolete for new PCs in the mid 90s. It is still used in embedded systems, but Intel will stop making it in 2007.

You're right. I have an old 486SX-25 dated back to 1989.

AppleMacReporter 15:57, 29 December 2006 (UTC)

I have recently heard about a multiprocessor-capable 486, but the article does not mention it. Can someone confirm its existence or nonexistence? - Anonymous 19:14, 17 May 2007 (UTC)

Look at Sequent Computer Systems; Alecv 12:07, 18 May 2007 (UTC)
Thanks. So, the CPU didn't itself provide support for SMP operation, but engineers at Sequent had implemented it "around" the stock processor with their own supporting hardware, if I understand correctly? Also, I believe those Sequent's SMP systems should be (briefly) mentioned here, in the 486 article. - Anonymous 01:04, 19 May 2007 (UTC)
OTOH, when I think about it, in times of sequential, in-order execution CPUs, not much support for SMP should be needed on the CPU side besides simple, bus-locking memory access primitives like XCHG (and in 486 even more powerful LOCK XADD and LOCK CMPXCHG). - Anonymous 01:10, 19 May 2007 (UTC)

[edit] Differences between the 386 and 486

Can anyone put a full command set difference list ? Sometimes it called 486+. AFIAR, 486 command set contains BSWAP command to translate a big endian "network order" data. Alecv 20:28, 23 May 2007 (UTC)

Correct. It also added some instructions very useful for synchronizing concurrent computation (f.e. SMP) like XADD and CMPXCHG. Later generations of 486 also added the CPUID instruction. There were some other additions, but not many, and I don't remember them all. I'll try to find out the full list and add it here. - Anonymous 14:47, 30 May 2007 (UTC)
Alright, seems my memory is better than I suspected :). I forgot only three instructions, all of them for low-level operating system use. That would be INVD, INVLPG, WBINVD. Hope the list helps you. - Anonymous 15:53, 30 May 2007 (UTC)