xdaniel

Hey there~

📜 Hobby programmer, ROM hacker, retro computers & consoles, anime & manga fan, sometimes NSFW?

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cathoderaydude
@cathoderaydude

the 80486 CPU is interesting because saying something is "as fast as a 486" is essentially meaningless. they were sold in speeds from 16 to 100 MHz, at a time when clockspeed was almost a pure indicator of true performance. that's more than a sixfold difference in speed. so if you run Doom on a 486SX-25, it'll be nearly unplayable; on a 486DX4-100, it'll run better than many Pentiums.


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in reply to @cathoderaydude's post:

Intel made an i487SX that was marketed as a separate FPU for the i486SX, but was actually just an i486DX which confirmed the presence of the other 486 and then turned it off, becoming the main processor from the FPU slot? lmaooo what even was early 90's computing...

also the DX4 series were actually running a 3x clock multiplier, I guess because 4 sounds more impressive than 3, which definitely backfired on at least one huge dork who took it to mean the 100 was running on a 25MHz FSB and therefore in some sense "inferior" to a DX2/66

that'd be silly. but also i have no idea and also want to know. it's so little transistors by modern standards that it'd probably be far more power efficient than ARM1 was. actual performance would not be very good though

The 486 is weird to me because it's the first widespread intel processor generation that didn't really change much from the programmer's perspective, but at the time, every new processor really felt like a massive jump. Like when I saw that the recent Pocket 386 handheld could run Windows 95, that feels impossible. 386s ran Windows 3.1, 486s ran Windows 95. (I didn't learn that 286s could run Windows 3.1 until a few years ago.)

But the 486 ISA added, like, six instructions? A handful of simple atomic operations and cache-management stuff. It was just faster; internally more efficient and able to be driven by higher clock speeds. The vast majority of programs from the 486 era are gonna run on a 386; realistically CMPXCHG is only gonna show up in a handful of places in some core libraries that can have very reasonable alternate 386-compatible implementations.

Meanwhile the 286 was a massive overhaul to add a 32-bit mode to the 8086, and then the 386 was another massive overhaul to make that usable, both by being allowed to switch back to 16-bit mode without rebooting the processor, and by adding software-controlled 8086 virtualization, which made all kinds of absurd shenanigans possible. It's a whole different computer. Stuff that needs a 386 needs a 386.

Oh jeez you are right! It added a whole 4 bits to the 8086's 20-bit address bus. I had assumed that 286 protected mode would give you a flat address space, but, no?? You still have the same sad set of 4 segment registers??? God, the 286 really just made every possible mistake at once, didn't it.