DR and MS DOS 5 and later have a 386 memory manager which can put an x86-32 CPU into Virtual 86 mode, remap RAM over any unused blocks in the I/O and ROM area (between 641kB-1024kB) to make Upper Memory Blocks, and load small resident parts of the OS into those blocks in order to keep as much base memory (0kb-640kB) free.

These memory managers could also turn the extended memory (above 1024kB) into managed XMS or EMS memory. LIM EMS was accessible to DOS apps and XMS to DOS-extender apps.

These were killer features in 1990 or so, and I made good money from optimising DOS memory for clients around that time.

Just replying with a web page showing the 80386 has having control registers doesn't imply that MS-DOS used them in any meaningful way.

The MMU is inside the processor. Any operating system running on an 80386 or higher has set registers/tables and gets hardware provided memory management.

If it uses it. Later versions of DOS did very little with the features the 386 offered, which is why there were MS-DOS extenders.

https://en.m.wikipedia.org/wiki/DOS_extender

You can make your own minimal DOS Extender just by setting those registers. This is what some games did.