Path: utzoo!mnetor!uunet!husc6!yale!cmcl2!brl-adm!umd5!uvaarpa!mcnc!mru
From: mru@mcnc.org (Markus Ruppel)
Newsgroups: comp.sys.ibm.pc
Subject: Re: PC-MOS....true ???
Message-ID: <576@speedy.mcnc.org>
Date: 15 Mar 88 00:34:29 GMT
References: <521@wa3wbu.UUCPo <923@unccvax.UUCP> <1650@uhccux.UUCP>
Reply-To: mru@mcnc.org.UUCP (Markus Ruppel)
Organization: Microelectronics Center of NC; RTP, NC
Lines: 73

In article <1650@uhccux.UUCP| yuan@uhccux.UUCP (Yuan Chang) writes:
|]-----This is my original posting (Markus Ruppel)
|]I haven't seen a MU ( multiuser version )  of PC-MOS so far !
|
|	It is being advertised.

That doesn't mean that you can order it or even work with it.

|
|]This is impossible ! On an XT for example there is no way to trap 
|]direct screen writes of applications, because the 8088/86 doesn't 
|]support any kind of memory protection levels ( as the - brain damaged
|]- 80286 and - much better - 80386 do ) .
|
|	Check what you know before you write.  PC-MOS on '386 machine 
|will be able to trap writes to video RAM.  Also there are programs 

I think if I should check what I write you should check what you answer.
:-)
My above statement was targeted to a 8086/88 and I assume it should be
obvious from the '(....)'-text that I recognize the abilities of a 80386.

|included with PC-MOS (and Multi-Link) that'll modify your program to
|use BIOS to write to screen, instead of direct memory writes.  

I have a problem to imagine a program which checks another program for
direct screen/memory writes. Are they replacing every MOV instruction which
has a destination in the adapter address space and create BIOS ints 
to move byte by byte or what. What if the same loop to MOV to the display
adapter is used to move data around inside the program, just with a 
different destination ?

Any responses on this aspect are aprreciated,
esp. from a PC-MOS expert.
 

|Problem
|is that not every program can be modified to do that, and that 
|graphic applications will *definitely* not run on a dumb terminal.

This might be the case for PC-MOS, but if you can run a terminal in 
PC-SCAN mode ( okay, it is not a dumb terminal anymore...:-) )  you
are able to run even a graphic application on a serial terminal.
Concurrent DOS for the 386 is able to do that.

|They do sell graphic terminals which can work with graphic applications
|though...  Also, most well-behaved programs will use BIOS to write to
|screen, instead of writing directly to memory.

But there are A LOT of unbehaved programs out there which go straight to
the screen.

|	
|]IT IS IMPOSSIBLE !!!!!!!!!!
|
|	Not totally.

Depending on your hardware  !
  
| 
|	There are restrictions.  Best way of running multi-user/multi-
|tasking applications is to run Xenix.  MS-DOS programs just aren't
|written to be multitasked ('386 can get around that, but a '286
|can't).  

But if you have invested in DOS apps during the last 5 years, Xenix
is not the best choice.

|
|-- 
|Yuan Chang 

Markus