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Questions tagged [80486]

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15 votes
1 answer
3k views

What's the story behind the "mysterious" 486DX3?

As I was skimming through an old MS-DOS game's README, I stumbled upon this: Therefore, we reccomend a newer 486-100 or better, preferably with a large external cache. Best performance will result ...
aybe's user avatar
  • 7,102
21 votes
2 answers
2k views

Did 486 SMP systems provide Total Store Ordering?

Cache-coherent SMP (symmetric, or shared-memory, multi processing) systems can provide various grades of memory ordering guarantees, the stronger ones being more expensive but making it easier to ...
rwallace's user avatar
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6 votes
1 answer
571 views

How did AMD Am386 and Am486 outperform Intel's version of the same microprocessors?

This question is related to a previous one that has been asked here before (How did AMD's 386 and 486 perform like Intel's newer generation?) My question is-two fold: a) When AMD "...
interested22's user avatar
24 votes
2 answers
3k views

Detecting the version of i486 CPU

Detecting the CPU model has been easy since Intel added the CPUID instruction to their Pentium processors (and some late 486s). However, earlier CPUs did not have this feature, so software had to rely ...
DarkAtom's user avatar
  • 2,337
14 votes
1 answer
889 views

What sequence of instructions is the equivalent to `fcomip` on i486?

Do you perhaps happen to know, what would be the easiest way to modify my AEC-to-x86 compiler (you can run the core of it in browser: https://flatassembler.github.io/compiler ) to be able to target ...
FlatAssembler's user avatar
28 votes
8 answers
8k views

Why did x86 support self-modifying code in the 80s and 90s?

In this question, by 'self-modifying code', I mean software that writes to a section of code that the CPU will very soon fetch and attempt to execute. I am not here talking about the software ...
rwallace's user avatar
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23 votes
1 answer
2k views

How were the test registers used on the i386 and the i486?

The Intel 386 and 486 CPUs (and some clones too) had some test registers (TR3–TR7) which were used to test features like the TLB and caches. Starting with Pentium, these were replaced with MSRs (Model ...
DarkAtom's user avatar
  • 2,337
196 votes
1 answer
56k views

Why does trying to break into the NT 3.1 kernel reboot my 486DX4 machine?

I installed Windows NT 3.1 on a Compaq ProSignia 3080 system, because of several reasons: I know that this machine was running Windows NT 3.1 when it was in productive use. And I think this machine ...
Michael Karcher's user avatar
2 votes
2 answers
1k views

How do I slow down the emulation in VMware and make it go "proper fullscreen" for Windows 3.11?

I have just managed to find and install my native language versions of MS-DOS 6 and Windows 3.11 in a virtual machine, just as I had on my first computer: an IBM 486 DX2 66 MHz. VM software: VMware ...
Rothberg's user avatar
19 votes
2 answers
3k views

How did AMD's 386 and 486 perform like Intel's newer generation?

AMD really started to come into its own as a competitor to Intel around the time of the Intel 80486 introduction. AMD countered Intel by shipping the popular (at least with PC enthusiasts) Am386-40, ...
Brian H's user avatar
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13 votes
2 answers
1k views

In what year was my old, long-lost IBM PC made and which form factor/model was it?

I've spent a ridiculous amount of time and effort over the years just trying to figure out what exact IBM product I grew up with. At last, I've finally established for 100% certain that it was a: IBM ...
Hopeless Nostalgic's user avatar
49 votes
2 answers
12k views

Why does the 80486 take longer to execute simple instructions than complex ones?

The 80486 processor can execute many instructions in a single cycle, such as a register-to-register add instruction (ADD EAX, EBX, for example), which one would generally assume is fairly complex, ...
occipita's user avatar
  • 2,382
21 votes
2 answers
8k views

Why did Socket 3 have more pins than needed for the 486?

Intel's Socket 3, used for 486 processors, was a 19×19 pin grid array socket. However, all compatible processors, to my knowledge, used 17×17 PGA packages. What was the point of the extra pins around ...
Hearth's user avatar
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5 votes
3 answers
1k views

Bad floppy drive in T1910CS 486 laptop

I've recently picked up a Toshiba T1910CS 486 laptop. It's in OK shape, with a 500MB hard drive and DOS installed. I also ordered a USB floppy disk drive and some floppy disks so that I could install ...
Percy B's user avatar
  • 53
15 votes
1 answer
1k views

Were there 486SX revisions without an FPU on the die?

I know that the 486SX had its FPU disabled, maybe by binning 486 CPUs into those with and without functioning FPUs. But did Intel eventually make a 486SX revision without an FPU on the die?
Arne's user avatar
  • 1,274