An 8088 or NEC V20 replica/substitute with an 21st address pin and 64KB of SRAM would be cool.
That would allow XT users to have HMA on MS-DOS 5/6.
A missing A20 gate isn't that much of a problem to MS-DOS, really.
It's mainly CP/M era applications that need the address wraparound.
Edit:
The main thing the 386 was useful for was the expanded virtual memory space. It made multitasking much easier. It basically fixed the 286.
Hi, I think the 80386 is much more capable than most people know. By using segmentation, it can handle up to 64 TB of virtual memory.
The use of segmentation also allowed to designate segments as containing data and application code.
So there was memory protection based on segmentation, years before NX/XD Bit and Window's DEP were around.
Both 80286 and 80386 had same fathers, also, I vaguely remember.
So without the 80286, the 80386 wouldn't have existed in its final form, maybe.
The main use of the 80286 or iAPX286 was data processing systems, PBX systems and such. It wasn't designed for PCs yet.
The 80386, by contrast was designed to be like a mainframe. This made porting easier, 32-Bit code was previously being used in mainframe environments.
It completely skipped the application as a PC processor so to say, and somewhat overdid. 😉
It was more than what IBM wanted it to be, also, I think.
That's why, for some time, I think IBM had supported the 80286, at best. The 80386 made them afraid.
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