6 ms·

Intel 80386, part 1: Introduction

141 points by nikbackm 8y ago

smhenderson 8y ago
Raymond Chen is such a joy to read. I’m old and jaded enough to have very mixed feelings about Microsoft but it’s obvious they’ve had some very talented programmers over the years. If I didn’t get enough pleasure from using Microsoft software over the years as I did from other OS’s I certainly made up for it reading stories from MS folk like Raymond. As always a great and informative read!
martin1975 8y ago
Personally I was looking forward to an intro to TSR programs :)
barbecue_sauce 8y ago
For x86 information, I really enjoyed Xeno Kovah's OpenSecurityTraining courses for Intro and Intermediate x86. Recording quality is a bit spotty, but their whole YouTube channel is filled with great content.
- ngcc_hk 8y ago
  Do not see the point of the microsoft one but these video are great!
aswanson 8y ago
I wonder if when these processors were developed, from a hardware standpoint, did the engineering team contemplate Turing completeness and the theory of computation, or just try to satisfy a set of perceived customer needs.
- stan_rogers 8y ago
  If "tiring completeness" is supposed to read "Turing completeness", then including a conditional jump instruction of any sort completes the hardware requirement. The rest is about the number of conditions upon which that may be based and the access semantics, and that's where the CISC, RISC and hybrid approaches differ.
  - aswanson 8y ago
    Agreed. I'm just wondering if they followed some theoretical schema or just responded to evolutionary forces. Most likely the latter.
    - deleted 8y ago
      [deleted]
    - xenadu02 8y ago
      It’s a direct evolution from 4004, 8008, 8080, to 8086. There was no compatibility but you can see the inspiration. IIRC 8086 was assembly compatible with 8080 but not binary compatible. At the time superscalar, register-renaming, vector-capable, and out-of-order were distant dreams and RAM was faster than the CPU. Everyone wrote assembly so the CPU designs accumulated instructions to make life easier on assembly programmers. 8086 was actually a stop-gap. The architecture astronauts at Intel that thought real hard about design were working on the iAPX 482, which was a stack machine that supported garbage collection in hardware(!)
      - dboreham 8y ago
        432
- kccqzy 8y ago
  It's difficult (though not quite impossible) to make a non-Turing-complete processor and still have it do useful things. So by making a processor that can do useful things, you have made it Turing complete.
- burfog 8y ago
  They got Turing completeness in just the MMU. This was surely unintended, just like Turing completeness in C++ template expansion and Turing completeness in sendmail configuration files. Here you go, computation via continuous MMU faults without actually completing any instructions: https://github.com/jbangert/trapcc https://github.com/jbangert/trapcc https://www.youtube.com/watch?v=eSRcvrVs5ug https://www.youtube.com/watch?v=eSRcvrVs5ug
  - wolfgke 8y ago
    > They got Turing completeness in just the MMU. Since the amount of adressable memory on any CPU is finite, while a Turing machine needs in infinite band of memory, such claims of Turing-completeness of processors or in this case the MMU are clearly fraudulent. Only an abstract mathematical model can be Turing-complete - there exists no physical realization of a Turing-complete system/Turing machine and there will never be.
    - Sharlin 8y ago
      This is completely pointless pedantry. Everybody knows that, and nobody bothers to type "Turing-complete (up to memory constraints)" all the time. Real mathematicians do this all the time, taking shortcuts with the understanding that they could phrase it completely rigorously if it were necessary.
- kryptiskt 8y ago
  Turing completeness is easier to achieve than to avoid. If you have conditional branching and an unbounded store (memory is finite of course, but it's arbitrarily finite) it is Turing complete. So they may not have cared, but the analysis step would have been really simple. And if you don't want to bother with any formalia you can just implement Brainfuck (or less anachronistically you can go with FRACTAN), if it works you have something Turing complete.
kccqzy 8y ago
See also the second and third installment: https://blogs.msdn.microsoft.com/oldnewthing/20190122-00/?p=100755 https://blogs.msdn.microsoft.com/oldnewthing/20190122-00/?p=... https://blogs.msdn.microsoft.com/oldnewthing/20190123-00/?p=100765 https://blogs.msdn.microsoft.com/oldnewthing/20190123-00/?p=...
pjmlp 8y ago
My first owned PC, a 386SX at 20 MHz, quite a departure from the PCW 1512 at school computer club or the Timex 2068 at home. However I still kept a bit of envy from my friends having fun with their Amiga 500s.
- AnIdiotOnTheNet 8y ago
  I'm still envious of my friends with Amiga 500s. The Amiga just kind of does that to people.
userbinator 8y ago
The 80386 is unusual in that it supports multiple calling conventions It's unusual to speak of a processor as "supporting" any calling convention, given that they are simply a convention compilers may follow. The CPU doesn't care (and in the case of the 386 which has no return address prediction or special stack handling, it really doesn't matter) about such things as functions or procedures either, as you'll quickly realise if you read good optimised handwritten Asm. Instruction encoding is highly irregular. It looks very regular in octal: http://www.dabo.de/ccc99/www.camp.ccc.de/radio/help.txt http://www.dabo.de/ccc99/www.camp.ccc.de/radio/help.txt

141 points by nikbackm 8y ago

Raymond Chen is such a joy to read. I’m old and jaded enough to have very mixed feelings about Microsoft but it’s obvious they’ve had some very talented programmers over the years. If I didn’t get enough pleasure from using Microsoft software over the years as I did from other OS’s I certainly made up for it reading stories from MS folk like Raymond. As always a great and informative read!

martin1975 8y ago

Personally I was looking forward to an intro to TSR programs :)

barbecue_sauce 8y ago

For x86 information, I really enjoyed Xeno Kovah's OpenSecurityTraining courses for Intro and Intermediate x86. Recording quality is a bit spotty, but their whole YouTube channel is filled with great content.

ngcc_hk 8y ago
Do not see the point of the microsoft one but these video are great!

aswanson 8y ago

I wonder if when these processors were developed, from a hardware standpoint, did the engineering team contemplate Turing completeness and the theory of computation, or just try to satisfy a set of perceived customer needs.

stan_rogers 8y ago
If "tiring completeness" is supposed to read "Turing completeness", then including a conditional jump instruction of any sort completes the hardware requirement. The rest is about the number of conditions upon which that may be based and the access semantics, and that's where the CISC, RISC and hybrid approaches differ.
- aswanson 8y ago
  Agreed. I'm just wondering if they followed some theoretical schema or just responded to evolutionary forces. Most likely the latter.
  - deleted 8y ago
    [deleted]
  - xenadu02 8y ago
    It’s a direct evolution from 4004, 8008, 8080, to 8086. There was no compatibility but you can see the inspiration. IIRC 8086 was assembly compatible with 8080 but not binary compatible. At the time superscalar, register-renaming, vector-capable, and out-of-order were distant dreams and RAM was faster than the CPU. Everyone wrote assembly so the CPU designs accumulated instructions to make life easier on assembly programmers. 8086 was actually a stop-gap. The architecture astronauts at Intel that thought real hard about design were working on the iAPX 482, which was a stack machine that supported garbage collection in hardware(!)
    - dboreham 8y ago
      432
kccqzy 8y ago
It's difficult (though not quite impossible) to make a non-Turing-complete processor and still have it do useful things. So by making a processor that can do useful things, you have made it Turing complete.
burfog 8y ago
They got Turing completeness in just the MMU. This was surely unintended, just like Turing completeness in C++ template expansion and Turing completeness in sendmail configuration files. Here you go, computation via continuous MMU faults without actually completing any instructions: https://github.com/jbangert/trapcc https://github.com/jbangert/trapcc https://www.youtube.com/watch?v=eSRcvrVs5ug https://www.youtube.com/watch?v=eSRcvrVs5ug
- wolfgke 8y ago
  > They got Turing completeness in just the MMU. Since the amount of adressable memory on any CPU is finite, while a Turing machine needs in infinite band of memory, such claims of Turing-completeness of processors or in this case the MMU are clearly fraudulent. Only an abstract mathematical model can be Turing-complete - there exists no physical realization of a Turing-complete system/Turing machine and there will never be.
  - Sharlin 8y ago
    This is completely pointless pedantry. Everybody knows that, and nobody bothers to type "Turing-complete (up to memory constraints)" all the time. Real mathematicians do this all the time, taking shortcuts with the understanding that they could phrase it completely rigorously if it were necessary.
kryptiskt 8y ago
Turing completeness is easier to achieve than to avoid. If you have conditional branching and an unbounded store (memory is finite of course, but it's arbitrarily finite) it is Turing complete. So they may not have cared, but the analysis step would have been really simple. And if you don't want to bother with any formalia you can just implement Brainfuck (or less anachronistically you can go with FRACTAN), if it works you have something Turing complete.

kccqzy 8y ago

See also the second and third installment: https://blogs.msdn.microsoft.com/oldnewthing/20190122-00/?p=100755 https://blogs.msdn.microsoft.com/oldnewthing/20190122-00/?p=... https://blogs.msdn.microsoft.com/oldnewthing/20190123-00/?p=100765 https://blogs.msdn.microsoft.com/oldnewthing/20190123-00/?p=...

pjmlp 8y ago

My first owned PC, a 386SX at 20 MHz, quite a departure from the PCW 1512 at school computer club or the Timex 2068 at home. However I still kept a bit of envy from my friends having fun with their Amiga 500s.

AnIdiotOnTheNet 8y ago
I'm still envious of my friends with Amiga 500s. The Amiga just kind of does that to people.

userbinator 8y ago

The 80386 is unusual in that it supports multiple calling conventions It's unusual to speak of a processor as "supporting" any calling convention, given that they are simply a convention compilers may follow. The CPU doesn't care (and in the case of the 386 which has no return address prediction or special stack handling, it really doesn't matter) about such things as functions or procedures either, as you'll quickly realise if you read good optimised handwritten Asm. Instruction encoding is highly irregular. It looks very regular in octal: http://www.dabo.de/ccc99/www.camp.ccc.de/radio/help.txt http://www.dabo.de/ccc99/www.camp.ccc.de/radio/help.txt