China DOS Union

It seems Teacher Wengier really knows this inside out, so let me ask a question here:
What is real mode, and what is protected mode???

Actually, as for real mode and protected mode, the biggest difference is that the former can only directly access memory below 1MB, while the latter is not limited that way.

Then wouldn't msdos7.0 not be real mode???

I always thought real mode meant a mode that can delete itself (under DOS, can it delete command.com?), while protected mode is a mode that cannot delete itself (like how in win2000 you can't delete win2000's files)!!! Is that right???

Not quite. Real mode is the 16-bit true DOS mode, and protected mode is the 32-bit 386 virtual mode. In the latter, all of the computer's memory can be accessed. But protected mode requires a protected mode server, for example: EMM386, DOS4GW, CWSDPMI, etc.

Then by that logic there is no such thing as protected mode in windows!!! Because there is no EMM386, DOS4GW, CWSDPMI, etc. in windows.

(No matter what mode, isn't it all talking about the operating system!!! You might as well just tell me which operating system is which mode) (and also the differences in functions between operating systems in different modes -- for example, whether it can delete itself -- I always feel that when windows gives an error while deleting its own files, that's an expression of protected mode!!! Please clear this up!!!)

That's not how it works... how could there be no emm386 in win? What wengier said is aimed at dos... it can't be defined the way you put it. If we boot DOS using its three basic core files, then at that point it is real mode DOS. When we load programs such as emm386 or cwsdpmi after booting, DOS then becomes protected mode.... Now that I've put it this way, do you understand?

Yes, I understand now!!!
But I still don't know what the "protection" in protected mode actually looks like, or just how "real" real mode is! Hehe

Windows is of course also a protected-mode DOS program! For example, VMM32, KRNL386, etc. make Windows enter protected mode.

As for the definition of protected mode, have a look here:

"The 80386 has three operating modes: real mode, protected mode, and virtual 8086 mode. This article introduces the 80386 under protected mode and related programming topics. The basic concepts of 80386 registers, addressing modes, and instructions in real mode, unless otherwise specified, are still retained under protected mode.
Although the capabilities of the 80386 in real mode greatly exceed those of its earlier processors (8086/8088, 80186, 80286), only in protected mode can the 80386 truly bring its greater power into play. In protected mode, all 32 address lines are valid, allowing physical address space of up to 4GB to be addressed; the expanded memory segmentation management mechanism and the optional memory paging management mechanism not only provide hardware support for memory sharing and protection, but also provide hardware support for implementing virtual memory; it supports multitasking, enabling fast task switching and protection of the task environment; four privilege levels and a complete privilege checking mechanism can both realize resource sharing and ensure the security and confidentiality of code and data as well as task isolation; it supports virtual 8086 mode, making it convenient to execute 8086 programs."