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assembler
X-G
Member #856
December 2000
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IIRC, there's a mode that's sort of like "real mode under protected mode", too ... I forget what it's called though.

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imaxcs
Member #4,036
November 2003

Quote:

It's perfectly possible to write a multitasking SO that runs in 16bit real mode (I have done it at university). Programs can mess up the SO, since there's no protection, thought.

IMHO true for windows, but not for linux.

Evert
Member #794
November 2000
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Quote:

I'm not very sure about this one, but IIRC you can run real mode programs under a protected mode environment.

Yes - virtual 86 mode. Your computer appears to each real-modeprogram running as a unique system.

Oscar Giner
Member #2,207
April 2002
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Quote:

Quote:
--------------------------------------------------------------------------------
It's perfectly possible to write a multitasking SO that runs in 16bit real mode (I have done it at university). Programs can mess up the SO, since there's no protection, thought.
--------------------------------------------------------------------------------

IMHO true for windows, but not for linux.

You didn't understand me. I'm talking about writing a 16bit multitasking SO. An SO is 100% standalone, it doesn't run over another SO (it may use it to boot, like that DOS linux boot loader, and in our case we used DOS to boot our SO. Probably Windows won't let you boot another SO).

Evert
Member #794
November 2000
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Oscar: do you mean Operating System (OS)...? Otherwise I'm not sure I understand what you mean by SO...
Are you Spanish the same as French in having all your abbreviations andacronyms the other way round from the rest of the world? ;D

X-G
Member #856
December 2000
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Silly spaniards. :P

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Oscar Giner
Member #2,207
April 2002
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Quote:

Oscar: do you mean Operating System (OS)...? Otherwise I'm not sure I understand what you mean by SO...

Ah, sorry. Yeah, I mean OS. SO in Spanish (Sistema Operativo).

nshade
Member #4,372
February 2004

Thanks for the corrections. I haven't touched real mode in years. I'm running linux so I don't have access to the vector table anyway.

Also I know that when you are in protected mode. the vector table is still at the bottom of memory. When you switch modes, the memory isn't erased. When you go to and from any mode, the data is still there. I was tought that calling an interrupt in protected mode was a fruitless thing to do and to simply not do it

Side note:

Remember on a 286 when you switched into protected mode you coudn't switch back into real mode? Intel thought that no one would ever want to switch back to such a wonky memory system. Anyways UNIX was becoming popular around that time and it was more powerful than DOS anyway. Whay would you want to run a monolithic OS when you have protected mode, which was better.

That's to show how long Microsoft's been stangnating the computer software industry.

You could actually go back into real mode on a 286. You have to RESET THE CPU on the fly and code in such a way that you didn't trip the computer into doing a BIOS self-test on restart.

Good Times.

That's why the 286 has such a short lifesycle.

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