Because there are only limited number of candidate CPUs we can discuss them case by case.
I think everyone agrees that P5/P54C/P55C defines the essence of being a 586. Anything closely resembles these CPUs, such as K5, 6x86MX/MII, would be considered as 586.
The upper boundary gets blurred when we add K6 into consideration. Personally I think it's closer to PII and thus 686. Not sure about Winchip C6 and Rise mP6.
I am not sure if the line should be drawn above or below 6x86 and 6x86L. They both lack many Pentium instructions: RDMSR, WRMSR, RDTSC, and 6x86 also lacks CMPXCHG8B.
I don't have enough knowledge to classify Nx586.
I don't think MediaGX series would qualify as 586 due to its 30-33MHz system bus.

Although MediaGX boards did come with SDRAM slots.

feipoa wrote:

Although MediaGX boards did come with SDRAM slots.

According to the datasheet, MediaGXm, the MMX version of MediaGX, has 64bit SDRAM interface running at 66-100MHz, and it supports all Pentium instructions. So I think MediaGXm should be placed above the 586 line.
I can't find Cyrix-published MediaGX datasheet and the best one I can find says MediaGX has 30-33MHz bus with 64bit EDO interface. Along with the lacking of Pentium instructions I think MediaGX is a super-5x86 processor.

What did I do by bringing up MediaGX

What defines a 586 to me? A Pentium level CPU chip! Because that's what the Pentium was going to be before Intel wanted to put a trademarked name on it (you cannot Trademark a Number) - if they had not done that, it would have been called the Intel 80586 or 586 for short. TBH, I kind of wish they did that, when I started doing this retro-hardware thing in 2001, there was a lot of pretentious snobbery about Pentiums because if I was just ONE processor generation ahead of hwat I had (486) I would be able to do ANYTHING I wanted at that time in most people's minds (then I got a DX4-100 and proved them wrong, 🤣).

A 686 is the Pentium Pro and Pentium II -IV generation, I think, I don't think Intel focused so much on the numbering system anymore. By that point, CPU was now a household knowledge thing (at least after the little dancing Intel guys had their day in the sun on TV). And if you were a part of the culture - Pentium = good CPU, Celeron = Celery, and Pentium Pro = Super Expensive and Underpowered for what you pay.

So to me a 586 is any of the below (and more)
Intel Pentium 60/66/90/100/120/133/200/233/200mmx/233mmx
AMD K-5 P75/90/100/120/133/200/233/266

Basically, anything Socket 7, and Pentium or K5 branded. There may be more, but that's the only chips I've ever had that were true 586 chips. The rest were Super Socket 7 Athlons (AMD Athlon K6 266), or hopped up 486 chips (DX4-100 WB stuff and the AMD 5x86 PR-75 133)

I should point out that the K6 and the Athlon were very different under the hood - K6 was, architecturally, something like the bastard child of a Pentium and a P6, while the Athlon was more or less like a P6 internally, with a double-pumped bus and some other bits of trickery involved.

I consider the K6 to be a 586-class chip, but I can see why some wouldn't. It definitely isn't an Athlon, though. (The architectural differences are a big chunk of why the K6 was never as skookum, clock for clock, as its Intel competitors, but the Athlon was. Faster, even.)

I consider anything which runs in a SS7 board to be a 586 class, even a K6-3+ because it doesn't have cmov which prevents running i686 Linux Kernels. To me anything which runs in a socket 3 or older is a 486, socket 4 and newer would be 586 class until the slot 1/A 686 class CPUs arrive. The IBM/Cyrix586/POD have some 586 like features and blur the line but I'd still consider them to be 486 class. Interesting thread.

TandySensation wrote:

I consider anything which runs in a SS7 board to be a 586 class, even a K6-3+ because it doesn't have cmov which prevents running i686 Linux Kernels.

That's a good idea to separate 586 and 686.

The K6 is a RISC CPU that uses a x86 to RISC to x86 decoder "module" to convert x86 instructions internally. This sends converted instructions to several RISC "modules", each serving a separate function. Architecturally it bears little similarity to with either the P54 or the P6.

As such, I'd classify it as "686 compatible", but not a true 686 chip. Same for the AMD K5.

AMD (or nexgen? whomever designed the K5 and K6 originally) decided to split x86 instructions and send translated versions of these trough separate RISC modules, witch each unit / module only handling one or a few specific decoded x86 instructions. In comparison, the P54C, P55 and P6 chips are rather homogeneous. They decode x86 instructions "as they are", and only separate MMX and SSE instructions, using stand alone handlers that can only work with those respective instruction sets. In that sense, MMX / SSE handlers could be considered RISC modules...

Nexgen designed the K6 and K6-2. The K5 was an internal AMD project, borrowing heavily from the 29k RISC CPU. Both were RISC engines internally with an instruction decoder frontend, as was P6.

Cyrix and IDT continued to use native x86 instructions for the 686 and Winchip.

jade_angel wrote:

K6 was, architecturally, something like the bastard child of a Pentium and a P6

Quote of the month right there. Might even use it as my signature! (Crediting the speaker, of course)

All Socket 7 CPU's are 586's.
Even if they have some 686 features.
There are even S370 586 CPU's. (VIA C3 / IDT)

You can call the Winchip 2/3/Cyrix III Core also a "pimped" 486. 😁
They are designed for Low Transistor Count and use legacy FPU... like a 486 😁

creepingnet wrote:

What defines a 586 to me? A Pentium level CPU chip! Because that's what the Pentium was going to be before Intel wanted to put a trademarked name on it (you cannot Trademark a Number) - if they had not done that, it would have been called the Intel 80586 or 586 for short.

That's true. Thanks to this, the world of electronics was saved from total chaos.
It allowed different manufacturers to use the same naming scheme (just think of 555 timer, 74 series, 78xx linear regulators, etc,)
What makes me wonder: If they can't trademark numbers, then why they can trademark Latin/Greek numerals ?
Pentium is derived from Greek Penta, and the Latin suffix -ium.
https://en.wikipedia.org/wiki/Pentium

Jo22 wrote:

That's true. Thanks to this, the world of electronics was saved from total chaos. It allowed different manufacturers to use the […]
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creepingnet wrote:

What defines a 586 to me? A Pentium level CPU chip! Because that's what the Pentium was going to be before Intel wanted to put a trademarked name on it (you cannot Trademark a Number) - if they had not done that, it would have been called the Intel 80586 or 586 for short.

That's true. Thanks to this, the world of electronics was saved from total chaos.
It allowed different manufacturers to use the same naming scheme (just think of 555 timer, 74 series, 78xx linear regulators, etc,)
What makes me wonder: If they can't trademark numbers, then why they can trademark Latin/Greek numerals ?
Pentium is derived from Greek Penta, and the Latin suffix -ium.
https://en.wikipedia.org/wiki/Pentium

Hmm... does that mean they could have trademarked FiveEightSix?

brassicGamer wrote:

Hmm... does that mean they could have trademarked FiveEightSix?

I seriously don't know. Maybe they went away with it because Pentium is a mixture of two languages.
Or maybe the american law just doesn't care for other languages (ie, everything non-English is not considered common language).

Anyway, I wonder if Intel could also have come up with something like FiveHuitSechs.
Or maybe I'm just missing something ? Maybe Pentium alone isn't trademarked, but "Intel Pentium" is ?

That's really confusing. Wikipedia also mentions another explanation :"The suffix -ium was chosen as it could connote
a fundamental ingredient of a computer, like a chemical element, while the prefix pent- could refer to the fifth generation of x86."

So because if they "invented" or "discovered" something elemental, they were freely allowed to coin a name for it (and trademark it right away) ?