China DOS Union

DOS is a 16-bit system,
so in theory it should only support 64K RAM.
2^16=65536=64K
Why can DOS support 64M RAM?
(1024 times)

At present the maximum DOS supports is 4GB, using the XMS 3.0 specification.

Then by what method does it make DOS, which in theory should only support 64K RAM,
support 64M RAM or even 4G RAM?

Thanks

Real-mode DOS is 16-bit, but protected-mode DOS is 32-bit. That is to say, DOS is a mixed 16-bit and 32-bit operating system.

The following is quoted from Wengier's post on 2003-7-6 4:38:21:
Real-mode DOS is 16-bit, but protected-mode DOS is 32-bit. That is to say, DOS is a mixed 16-bit and 32-bit operating system.

But then how do you explain that real-mode DOS can use 1M of memory?

For real-mode DOS, if you want to access memory above 1MB, generally the only way is through XMS/EMS memory... But for protected-mode DOS, accessing memory above 1MB is much easier...

Nobody uses EMS anymore~

That is what is called extended memory.

I don't really know the terminology used in the mainland...
In Taiwan:
The Chinese translation of XMS is "extended memory"
The Chinese translation of EMS is "expanded memory"

Actually even in the mainland, the translations of XMS and EMS get mixed up, so it's much more convenient just to use XMS and EMS.

What I mean is only ordinary MS/PC/DR-DOS, not some new super DOS or DOS with some software added. Exactly what method is used to handle memory beyond 64K?
I firmly believe DOS is a 16-bit operating system, not a 16/32 mixed operating system.
Reason:
A 286 can use 2M, but it has no 32-bit capability, and DOS could already run on the 286.
So I believe DOS is not a 16/32 mixed operating system.
Rather, it uses some method to manage memory beyond 64K.

DOS really is a 16/32-bit mixed operating system! The real mode of DOS (except FreeDOS 32) is 16-bit, while 32-bit mode can only be realized when both hardware (386+) and software (DPMI/VCPI etc.) support it!

Therefore, without any software or drivers at all (including HIMEM.SYS, EMM386.EXE, etc.), DOS (except FreeDOS 32) cannot support 32-bit, nor can it access memory above 1MB. But once the hardware supports it, then by loading DOS memory/protected-mode drivers such as XMS, EMS, VCPI, DPMI, DPMS, DOS can completely do all of the above.

The following is quoted from Wengier's post on 2003-7-13 2:08:15:

Therefore, if there is no software or driver at all (including HIMEM.SYS, EMM386.EXE, etc.), DOS (except FreeDOS 32) cannot support 32-bit operation, nor can it access memory above 1MB. But once the hardware supports it, then by loading DOS memory/protected-mode drivers such as XMS, EMS, VCPI, DPMI, DPMS, and so on, DOS can fully do all of the above.

Then what about USB? Under what mode does a USB hard disk have to be in so that it can be properly activated and booted?

Then how does DOS handle 2M of memory on a 286?

Using 32-bit on a 286 computer is naturally not possible, but you can still use XMS, EMS, etc. to access memory above 1MB...