3 ms·

Author here for your Pentium questions :-)

by kens 2y ago

mesrik 2y ago
Hi Ken, Nice article. While reading I remembered that I watched some time ago the Oral History of Gary Davidian and he was quite bit involved with microcoding. And if I were you I would try asking him if he could be able to give you some ideas where to get more information about microcode workings and development. Here are links to that interview, if you have time to watch it. It's in two parts. - https://www.youtube.com/watch?v=l_Go9D1kLNU https://www.youtube.com/watch?v=l_Go9D1kLNU - https://www.youtube.com/watch?v=MVEKt_H3FsI https://www.youtube.com/watch?v=MVEKt_H3FsI Cheers, :-) riku
- nxobject 2y ago
  This is the Gary Davidian of the Classic MacOS PPC nanokernel, no? I wish I've had as much fun work as he's had in his career.
  - klelatti 2y ago
    Also the Gary Davidian of Intel vs NEC fame! https://thechipletter.substack.com/p/intel-vs-nec-the-case-of-the-v20s https://thechipletter.substack.com/p/intel-vs-nec-the-case-o...
vitalmixofntrnt 2y ago
Can I add my own instruction set extensions to the original x86 isa as implemented by the 8086 without permission from Intel and / or AMD as long as I'm not copying any x86 instruction set extensions?
- kens 2y ago
  I don't know the legal details here but I think you can do whatever you want as long as you're not violating any patents (good luck). Also, Intel claims a copyright on the mnemonics for 8080 and 8086 assembly language. Microcode is also protected by copyright.
- userbinator 2y ago
  Any patents on the 8086 have long expired, and so have the ones from the last century. As Ken says, the microcode is copyrighted but you don't need to use that to make a compatible version.
CalRobert 2y ago
Why wasn’t the Pentium’s successor the Sexium?
- kens 2y ago
  Ha ha. Internally, the successor to the Pentium (P5) had the codename P6, but it was called the Pentium Pro externally rather than anything six-related. Instead, Intel decided to go with an incomprehensible system of naming: Pentium Overdrive, Pentium MMX, Pentium Pro, Pentium II, Pentium III, Pentium III Xeon, Pentium D, Pentium M, Pentium Extreme Edition, etc. Good luck trying to figure out the ordering of these processors.
  - kragen 2y ago
    E5200.
  - ssl-3 2y ago
    Intel's bad naming is still shooting them in the foot today. For a company that butters their bread by selling new products, they're doing a spectacularly bad job of letting people know what the new hotness is. I hear things like "What do you mean it's slow? It's an i7!" or "It can't be slow -- it's a Xeon!" from too many people in the wild. To them, the first number is the important one. What they see is that it is still an i7 and therefore they think it must be still be (relatively) fast, even if their second-gen i7-2600 is demonstrably pretty slow. I tried once to explain how Intel's numbering system has worked to a friend. I failed pretty miserably. I even used a whiteboard. I couldn't convey what needed to be conveyed in order to explain why his computer (an i7) wasn't keeping up with the tasks he gave to it. But I can convey the problem simply enough in this crowd, here on HNN: What's faster, a "Core i3-9100" or a "Core i7-2600"? (At least with 286, 386, 486, and Pentium, the nomenclature was much more digestible.)
    - userbinator 2y ago
      What's faster, a "Core i3-9100" or a "Core i7-2600"? One has 4 threads, the other has 8; and the difference between 6 generations is actually not that big, especially if you start talking about overclocking, cooling, and thermal throttling. At least with 286, 386, 486, and Pentium, the nomenclature was much more digestible Those were all single-core, but still, you could ask "what's faster, a 486SX-16 or a 386DX-33?" (The answer may surprise you. Sorry, couldn't resist...): https://dependency-injection.com/the-slowest-486-vs-fastest-386/ https://dependency-injection.com/the-slowest-486-vs-fastest-...
uticus 2y ago
> If you have enough time, you can extract the bits from the ROM by examining the silicon and seeing where transistors are present. I'm curious if this is a better way than somehow scanning the ROM electronically? Asking based on my very shallow understanding of how ROM works in this situation, although I did read the bit about M1, M2, and M3 lines/contacts. [edit: I also read about the testing circuitry, that "runs through each address," but it's unclear if this is an auto feature running without being asked at startup, or if there is some way to tap into / intercept this functionality from outside.]
- kens 2y ago
  You could put microprobes on the die and read out the ROM contents electrically, but that would be difficult and would need specialized equipment. Reading out the ROM visually is much easier, and there is software that can interpret images if they are clear enough, e.g. maskromtool: https://github.com/travisgoodspeed/maskromtool https://github.com/travisgoodspeed/maskromtool The Pentium's built-in self test is somewhat documented: you pull the INIT pin high while the RESET pin goes low to trigger the test. You can also execute the RUNBIST instruction through boundary scan. I don't think this helps you get the ROM data; the test just reports pass/fail.
dreamcompiler 2y ago
Isn't the Pentium's microcode upgradable? Or is that only in later chips? These fixed transistors imply no upgradability.
- kens 2y ago
  Microcode updates were first implemented in the Pentium Pro. When the original Pentium had the infamous FDIV bug, the only fix was for Intel to replace the processors at a cost of $475 million.
  - sroussey 2y ago
    Good thing win95 came out soon after and filled everyone’s coffers from new equipment buying

Author here for your Pentium questions :-)

by kens 2y ago

Author here for your Pentium questions :-)

Hi Ken, Nice article. While reading I remembered that I watched some time ago the Oral History of Gary Davidian and he was quite bit involved with microcoding. And if I were you I would try asking him if he could be able to give you some ideas where to get more information about microcode workings and development. Here are links to that interview, if you have time to watch it. It's in two parts. - https://www.youtube.com/watch?v=l_Go9D1kLNU https://www.youtube.com/watch?v=l_Go9D1kLNU - https://www.youtube.com/watch?v=MVEKt_H3FsI https://www.youtube.com/watch?v=MVEKt_H3FsI Cheers, :-) riku

nxobject 2y ago
This is the Gary Davidian of the Classic MacOS PPC nanokernel, no? I wish I've had as much fun work as he's had in his career.
- klelatti 2y ago
  Also the Gary Davidian of Intel vs NEC fame! https://thechipletter.substack.com/p/intel-vs-nec-the-case-of-the-v20s https://thechipletter.substack.com/p/intel-vs-nec-the-case-o...

vitalmixofntrnt 2y ago

Can I add my own instruction set extensions to the original x86 isa as implemented by the 8086 without permission from Intel and / or AMD as long as I'm not copying any x86 instruction set extensions?

kens 2y ago
I don't know the legal details here but I think you can do whatever you want as long as you're not violating any patents (good luck). Also, Intel claims a copyright on the mnemonics for 8080 and 8086 assembly language. Microcode is also protected by copyright.
userbinator 2y ago
Any patents on the 8086 have long expired, and so have the ones from the last century. As Ken says, the microcode is copyrighted but you don't need to use that to make a compatible version.

CalRobert 2y ago

Why wasn’t the Pentium’s successor the Sexium?

kens 2y ago
Ha ha. Internally, the successor to the Pentium (P5) had the codename P6, but it was called the Pentium Pro externally rather than anything six-related. Instead, Intel decided to go with an incomprehensible system of naming: Pentium Overdrive, Pentium MMX, Pentium Pro, Pentium II, Pentium III, Pentium III Xeon, Pentium D, Pentium M, Pentium Extreme Edition, etc. Good luck trying to figure out the ordering of these processors.
- kragen 2y ago
  E5200.
- ssl-3 2y ago
  Intel's bad naming is still shooting them in the foot today. For a company that butters their bread by selling new products, they're doing a spectacularly bad job of letting people know what the new hotness is. I hear things like "What do you mean it's slow? It's an i7!" or "It can't be slow -- it's a Xeon!" from too many people in the wild. To them, the first number is the important one. What they see is that it is still an i7 and therefore they think it must be still be (relatively) fast, even if their second-gen i7-2600 is demonstrably pretty slow. I tried once to explain how Intel's numbering system has worked to a friend. I failed pretty miserably. I even used a whiteboard. I couldn't convey what needed to be conveyed in order to explain why his computer (an i7) wasn't keeping up with the tasks he gave to it. But I can convey the problem simply enough in this crowd, here on HNN: What's faster, a "Core i3-9100" or a "Core i7-2600"? (At least with 286, 386, 486, and Pentium, the nomenclature was much more digestible.)
  - userbinator 2y ago
    What's faster, a "Core i3-9100" or a "Core i7-2600"? One has 4 threads, the other has 8; and the difference between 6 generations is actually not that big, especially if you start talking about overclocking, cooling, and thermal throttling. At least with 286, 386, 486, and Pentium, the nomenclature was much more digestible Those were all single-core, but still, you could ask "what's faster, a 486SX-16 or a 386DX-33?" (The answer may surprise you. Sorry, couldn't resist...): https://dependency-injection.com/the-slowest-486-vs-fastest-386/ https://dependency-injection.com/the-slowest-486-vs-fastest-...

uticus 2y ago

> If you have enough time, you can extract the bits from the ROM by examining the silicon and seeing where transistors are present. I'm curious if this is a better way than somehow scanning the ROM electronically? Asking based on my very shallow understanding of how ROM works in this situation, although I did read the bit about M1, M2, and M3 lines/contacts. [edit: I also read about the testing circuitry, that "runs through each address," but it's unclear if this is an auto feature running without being asked at startup, or if there is some way to tap into / intercept this functionality from outside.]

kens 2y ago
You could put microprobes on the die and read out the ROM contents electrically, but that would be difficult and would need specialized equipment. Reading out the ROM visually is much easier, and there is software that can interpret images if they are clear enough, e.g. maskromtool: https://github.com/travisgoodspeed/maskromtool https://github.com/travisgoodspeed/maskromtool The Pentium's built-in self test is somewhat documented: you pull the INIT pin high while the RESET pin goes low to trigger the test. You can also execute the RUNBIST instruction through boundary scan. I don't think this helps you get the ROM data; the test just reports pass/fail.

dreamcompiler 2y ago

Isn't the Pentium's microcode upgradable? Or is that only in later chips? These fixed transistors imply no upgradability.

kens 2y ago
Microcode updates were first implemented in the Pentium Pro. When the original Pentium had the infamous FDIV bug, the only fix was for Intel to replace the processors at a cost of $475 million.
- sroussey 2y ago
  Good thing win95 came out soon after and filled everyone’s coffers from new equipment buying