The 486SX

It’s not just COVID-19 vaccines receiving large quantities of disinformation. Even the 486SX has its own Holocaust Deniers. I couldn’t believe this popped up again months ago.

Image by Michael Schwarzenberger from Pixabay

The time honored (and correct) tale of the 486SX was that the original units were 486DX chips with a defective math co-processor. With every new chip design, especially back there and back then, there was always a bit of a yield problem until the manufacturing process got worked out. Many times you ended up with junk. INTEL got lucky with this defect. Since these chips weren’t technically “scrap” because everything other than the math co-processor worked, they stock piled them. Even in this state, it was an enhanced 386 processor so it wasn’t without value.

This tale was widely reported at the time. It is still reported today.

In April of 1991 Intel launched the Intel i486SX chip, bringing a lower-cost processor to the PC market. It was a modified i486DX with the FPU (floating-point unit) disabled. In fact, all early were in fact i486DX chips with a defective FPU, with the the FPU’s power and bus connections were destroyed with a laser.


Hopefully you will click the link and scroll down to read what the i487 really was. Here are some other links to read if you wish.

Google books

Another Google books

Yet Another Google books

Even Byte Magazine told the 486SX story.

Even economists know the story of the 486SX.

Now we will check in with Nutter Central

Every time I hear this stuff spewed or see it written I cannot help thinking about the Armadillo Hat Wearing Guy from Dukes of Hazzard.

===== Nutter Central
This has widely been debunked.

The SXs were introduced to the market years after the introduction of
the DXs. Intel didn’t start to have massive production problems all of a
sudden and thus decided to pull this stunt. The SXs were designed to
have the FPU disabled, and their FPU was for this reason ever tested.
The only reason for the introduction of the SX was market segmentation
to compete against AMD.

Here’s some links for you, given you seem to able to Google “486 sx
defective” (and leave it in the URLs that you link), but somehow
conveniently IGNORING the first couple of results, even if they include
first-hand accounts of Intel engineers who worked on the 486 that
disprove the whole defective story:

By the way, did you notice that the Wikipedia page that YOU linked
doesn’t talk about those chips being “defective” DXs?
Because that’s a lie, as discussed in the talk page:


Back to Reality and Case Studies

When you take some business courses covering how to turn failure into profits the 486SX is generally one of the cases discussed. Here are some others:

  • Sony Walkman: A shiny new VP combined a failed portable tape recorder that couldn’t record with an earbud/headphone set that had no market. Both R&D failures that, when combined became a highly profitable.
  • 3M Post-It Notes: Engineers and scientists set out to create a glue so strong it made Crazy glue look like Elmer’s School Glue. They took the path of exponentially increasing the length of time to dry. The end result was it never really dries and bonds. It was a complete failure until someone used it to glue little yellow pieces of paper together in the form of note pads. People found you could stick them to anything and they would come right off.
  • Gasoline: This was largely a byproduct of making heating and lamp oil. It was dumped into rivers and burned off . . . Until Henry Ford came along.
  • Vulcanization: Mr. Goodyear meeting investors in a shed that had a wood stove for heat was raging that they wouldn’t give him more money. Rubber tires were so flimsy and blew out so often that “can I kick the tires” became a phrase in American culture. Flinging his new hunk of rubber around while hollering and gesturing with his arms, it landed on the hot wood stove. After scraping it off the stove they found the result was still flexible and far more impervious to cuts. He got his money.

I read a book covering that stuff years ago, but cannot remember the title. No, it wasn’t this economics book.

Interesting Take and Source of Confusion

Wikipedia has an interesting take on the 486SX. It is only interesting because it has this phrasing.

AMD had begun manufacturing its 386DX clone which was faster than Intel’s. To respond to this new situation Intel wanted to provide a lower cost i486 CPU for system integrators, but without sacrificing the better profit margins of a “full” i486. This was accomplished through a debug feature called Disable Floating Point (DFP), by grounding a certain bond wire in the CPU package. The i486SX was introduced in mid-1991 at 20 MHz in a PGA package. Later (1992) versions of the i486SX had the FPU entirely removed for cost-cutting reasons and comes in surface-mount packages as well.

Every story said they were defective 486DX chips, even this one. Whether the defect happened due to manufacturing error or by “grounding a certain bond wire in the CPU” what was initially sold as the 486SX was a defective 486DX. The nutters also overlook the fact that nothing stopped INTEL from taking 486DX chips that really did fail FPU testing and sending them down the 486SX line that disabled the non-functioning FPU.

My Tidbit

Prior to DEC releasing the first Alpha computers I was doing a project for Digital Equipment. Sometimes I was in the Elk Grove Village office and sometimes out at the client site in Melrose Park. When I was in the office, across the hall from where I sat was one of the many people working on the first Alpha computers. Cannot find a picture of the one I used to own or remember the exact model. Many looked like this.

DEC Alpha running Windows NT

You could firmware swap the console on these types of workstations. One console allowed you to run Windows NT special built for the Alpha (Microsoft actually preferred using the Alpha for development.) The other let you run OpenVMS. Technically I wasn’t supposed to see any of the stuff I saw, but the boys and girls at DEC liked me.

Sometimes a group of us would have lunch in the cafeteria. One day, one of the people who joined our table said he was working on the 486SX “Dandy.” He volunteered that Intel had told them the 486SX was a DX with a defective FPU.

Let me stress this part. Nobody cared. If those chips couldn’t be sold they would be scrapped. E-waste was a problem even back then. Giant tube type monitors failed after a few years. Newer, better, faster, computers were being announced every six months or so. By iPhone standards, we weren’t throwing as many units away, but they were much bigger units.

I really like the write-up CPU Museum has on these chips. Lots of nice pictures with details links. They don’t wade into the argument, they just move on.

Here’s the Reality

It was all of the above and you can prove it to yourself.

Simply go to Google Books and search for all of the trade rags printed during 1991. Computer World, Computer Shopper, PC Magazine, Info World, Byte, etc. You want to focus your attention (usually) on the “Letters” sections. It won’t take long for you to realize that INTEL had a team dedicated to reading the weekly trade rags and writing a polite nasty-gram each and every time the magazines published something unflattering about INTEL.

When you find a letter from INTEL take a quick glance at the previous article they are complaining about from the previous issue. Won’t take you long. I seem to remember the longest articles ever published in those things not exceeding an office bathroom trip.

After you have come to the same conclusion that INTEL had an entire group whose job it was to bitch about bad press use the search utility to find 486SX articles stating they are defective 486DX chips. Now look at the “letters” section for the next month. Not once do I remember reading a nasty-gram from INTEL complaining about the magazines claiming 486SX chips were defective 486DX chips initially. Search for yourself. Do the other search first though. You need to get a feel for just how hard INTEL beat back bad press. If it wasn’t “true enough” they wouldn’t have let it slide.

Disabling or Disabled

Personally, I’m willing to believe it was all of the above when it came to the disabling of the FPU. A robot or mechanically controlled laser (that they probably already had laying around) to do the much rumored cutting on the defective 486DX chips was logically the shortest path to 486SX production. They had no idea how well these were going to sell. If AMD hadn’t release a better 386 than INTEL had on the market, below the 486DX price point, INTEL might not have been shamed into releasing the 486SX. Really depends how high the pile of 486DX processors with defective FPU got.

Setting up a line to “ground a certain bond wire” would not have been a risk worth taking until they could know how well the 486SX would sell. The nutters never consider the fact that “bond wire” story did get out. I was active in the BBS world back then. There were lots of students enrolled in the electronics hardware programs at DeVry and other schools. Not once did I ever hear of any “hacked” or “unlocked” 486DX chips on the market.

Dudes would have tried that!

We were putting RLL controllers on Miniscribe MFM drives because we found out the MFM model numbers that corresponded to the RLL certified models. We were all young and dumb back then. Willing to fry something just to see if it would work. I fried two of those drives. Actually I fried the same pair of drives twice. There was a place you could send them to that would replace the one chip that would burn out in the on-drive logic board. You got over a year out of them doing that. You rarely got five years out of a hard drive back then anyway.

Overclocking isn’t something new.

You have firmware accessible from the keyboard to overclock now. We had dudes tweaking motherboards.

Even today I cannot find anyone claiming they made such a conversion from 486SX to 486DX. I can only find one mention of the “drill a hole in the right place” and that is as much as they mention. There would have been something on the BBS Echomail networks and it would have survived to the Internet Achive.

Roland Hughes started his IT career in the early 1980s. He quickly became a consultant and president of Logikal Solutions, a software consulting firm specializing in OpenVMS application and C++/Qt touchscreen/embedded Linux development. Early in his career he became involved in what is now called cross platform development. Given the dearth of useful books on the subject he ventured into the world of professional author in 1995 writing the first of the "Zinc It!" book series for John Gordon Burke Publisher, Inc. A decade later he released a massive (nearly 800 pages) tome "The Minimum You Need to Know to Be an OpenVMS Application Developer" which tried to encapsulate the essential skills gained over what was nearly a 20 year career at that point. From there "The Minimum You Need to Know" book series was born. Three years later he wrote his first novel "Infinite Exposure" which got much notice from people involved in the banking and financial security worlds. Some of the attacks predicted in that book have since come to pass. While it was not originally intended to be a trilogy, it became the first book of "The Earth That Was" trilogy: Infinite Exposure Lesedi - The Greatest Lie Ever Told John Smith - Last Known Survivor of the Microsoft Wars When he is not consulting Roland Hughes posts about technology and sometimes politics on his blog. He also has regularly scheduled Sunday posts appearing on the Interesting Authors blog.