jakethompson1 wrote on 2025-03-30, 00:30:
I would probably draw the line at systems meeting the Microsoft PC97 and other specs, when their dictated Windows compatibility switched from minimum specs to things you aren't allowed to have.
Such as: text mode POST screen, non-ISAPnP ISA cards in the system (eventually no ISA slots allowed at all), etc.
That was the final nail in the coffin, right.
What I meant was more of change of direction, rather that a hard shift.
A 586 PC with a 586 motherboard still was quite DOS compatible, but DOS nolonger was the leading platform.
The extensions were made with Windows (95) in mind, rather.
When 486 PCs were at their height, the 486 motherboards were normally just industry standard PC/AT compatibles. With ISA or VLB bus.
No PCI, no Plug&Play, except for ISA Plug&Play (arrived late).
Edit: VIP boards came late. Opti Local bus was like VLB in its functionality.
Things like floppy controller, IDE and serial/parallel ports were on dedicated multi-i/o cards.
The chips were discreet, dedicated industry standard chips.
Something like an 16450 or 16550AFN FiFo and an UM82C11 parallel port IC.
With the Pentium motherboards, things like Super I/O chips and LPC bus became more dominant.
There was a shift from 5v to 3.3v, also, which got even harder with ATX specification.
In 486 days, the processors were still general purpose processors also.
You had ethernet routers based on 486SXL running some Unix style OS, for example.
All in all, the classic PC/AT architecture was built with 286/386/486 processors.
The 586 itself wasn't so much the deviation, but what came with it at the time (586 motherboards, BIOS extensions, USB, AGP etc).
A 586 combined with a classic AT style mainboard (without PCI) is very compatible and not worse than a 486DX4-100 in terms of compatibility.
Rather contrary, things like VME and enhanced x87 FPU can even enhance everything and make things run smoother.
So again, I don’t blame the Pentium (586) CPU at all. It's fine for DOS.
It's just the changes that ATX motherboards brought with them.
(I know that ATX is mainly a form factor, but it also introduced other things like power connector, the concept of the back panel etc.)
Edit: If I was being accurate, then I should have said that the 386 platform in the 80s already was meant for a "next gen OS".
But the "super DOS" that eventually became OS/2 was delayed and still very dependent on standard hardware - like good old DOS was.
Early Windows NT 3.x was similar, I think. It needed industry standard hardware to run well.
With the advent of Pentium PCs and Windows 95, the standards got watered down.
Strict compatibility at hardware level nolonger was as much of a requirement as it used to be.
Instead, multimedia and Plug&Play and Windows 95 was important.
Early Linux users got to experience this soon.:
There was a saying that Linux needs "good hardware", which more than often was pre-USB era hardware.
Or "scrapyard hardware" as we non-Linux users used to joke. 😉
PCs with SCSI controllers and solid graphics cards with VBE support were considered good.
ACPI was an issue often, so that -noacpi switches got more common.
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