From: josepva AT informatica DOT TELERJ DOT net DOT br
Message-ID: <39AE1D927549D111A88F00A0C94B9C7D628EC9@RJ01MAI01>
To: djgpp AT delorie DOT com
Subject: RE: paradox!
Date: Fri, 29 Jan 1999 14:27:34 -0200
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Reply-To: djgpp AT delorie DOT com

Hi Mohamed,

> ----------
> De: 	Mohamed El-dawy[SMTP:msdawy AT hotmail DOT com]
> Enviada: 	Sexta-feira, 29 de Janeiro de 1999 11:53
> Para: 	djgpp AT delorie DOT com
> Assunto: 	paradox!
> 
> Hi all,
>    How are ya all? hope u r all perfectly okay!
> 
>    Here are some questions!! :-)
>  
> 1) what is _djgpp_conventional_base? there is a mention of it in the FAQ 
> but i dunno what it is! is there any explanation of it in the help 
> files? which file? i couldn't find any explanation for it anywhere!! 
> perhaps because i dunno how to search well!  :-(
> 
I readed in somewhere in FAQ that there is a default selector that address
all and only first 1MB of memory.

> and here is a simple paradox...
> 
> (please correct me if i am wrong in any point here! I am not really 100% 
> sure of what i am writing!)
> the 386 has some models of operation. of which i am only interested in 
> two, the segmented model, and the flat model. I have understood that the 
> flat model is the same as the segmented but with all segments set to the 
> same values (i.e. they all point to the same descriptor). they all begin 
> at 0 and span 4gb, right?
> Now...
> a) is there any kind of protection when using the flat mode? how comes? 
> all the memory is available and i can write to anywhere without causing 
> an exception!
> b) I assume djgpp runs in flat model! right? this is copied from faq...
> >Programs compiled with DJGPP can access all the physical memory on your 
> >machine and support virtual memory. All this memory presents a flat 
> address 
> >space with no segmentation (you can say goodbye to far and huge 
> pointers 
> >and to memory models), and is only limited by the amount of virtual 
> memory 
> >supported by the DPMI server in use.
> 
I think that all the DPMI servers use segmentation and DJGPP too!

> great... now all the memory is available! why do i get a SIGSEGV fault 
> when i executed a very simple CLS function?
> mov edi,0xa0000
> mov ecx,16000
> mov eax,0
> rep stosd
> 
Try to read a little more the FAQ and you will see the answers for your
questions.

> I am puzzled!
> 
> 3) where can i find info about pages, page table... etc... i have read 
> intel reference, but i couldn't understand any thing!! :-(
> 
Neither the Intel Engineers understand the Intel reference!

> looking forward to hearing from u soon... ;-)!
> 
I know that I was not of a great utility as I'm a Newbie too, but, I hope
that I wrote to you be usefull.

> with lots of luv,
>    Mohamed El Dawy
> 
José Paulo
Rio de Janeiro - Brazil
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