jbjones@marlin.NOSC.MIL (John B. Jones) (09/14/89)
In article <513@nixpbe.UUCP> freiss@nixpbe.UUCP (freiss) writes: > >I'm looking for book references and / or source code snippets of >programs for the 80286 in protected mode. What is protected mode? Is there an unprotected mode? It sounds like some programming term, but what's it for? Thanks in advance for turning some lights on. john jbjones@marlin.nosc.mil.UUCP
gcook@cps3xx.UUCP (Greg Cook) (09/14/89)
From article <1219@marlin.NOSC.MIL>, by jbjones@marlin.NOSC.MIL (John B. Jones): > In article <513@nixpbe.UUCP> freiss@nixpbe.UUCP (freiss) writes: >> >>I'm looking for book references and / or source code snippets of >>programs for the 80286 in protected mode. > > What is protected mode? Is there an unprotected mode? It sounds like > some programming term, but what's it for? > Thanks in advance for turning some lights on. Interesting that I just read a blurb in PC Computing (aug 1988) about ten minutes ago that mentioned this. It goes as follows: The 80286 is capable of multitasking when run in its protectd mode, which assures that one application won't corrupt the memory owned by another application. They also go on to say that this cannot be used int the DOS environment. That's all I know about it, if anyone can shed any further light, please do. ========================================================================= Greg Cook All good things come through chemistry! gcook@horus.cem.msu.edu cook@frith.egr.msu.edu
ppa@hpldola.HP.COM (Paul P. Austgen) (09/14/89)
Protected mode is where the full address space of the 80286 is used. DOS does not run the processor in this mode, although note that certain programs such as VDISK can switch into it to address extended memory.
erck12@castle.ed.ac.uk (Gnome) (09/15/89)
In article <1219@marlin.NOSC.MIL> jbjones@marlin.nosc.mil.UUCP (John B. Jones) writes:
-What is protected mode? Is there an unprotected mode? It sounds like
-some programming term, but what's it for?
-Thanks in advance for turning some lights on.
As far as I know (and most of this knowledge is 2nd hand) the 80286 can
operate in two modes, protected and unprotected. The former of these is the real
80286, while the latter, which is used by DOS, makes it act like a 8086/88. The
term protected comes from the protected memory scheme available in that mode.
This is needed by multi-tasking operating systems to stop one process
corrupting anothers memory. OS2 uses protected mode, except when the DOS box is
active. If you think all this is complicated the 80386 has four modes! It has
the two suported by the 80286, true 80386 mode, and multi-8086 mode (which
simulates an individual 8086 in each 1M of the memory map - nice!). I hope the
lights are at least glowing now.
--
Geoff Ballinger, JANET: Geoff@Ed.Ac.Uk
CS/AI, ARPA: Geoff%Uk.Ac.Ed@nsfnet-relay.Ac.Uk
Edinburgh University. UUCP: ...!uunet!mcvax!ukc!Ed.Ac.Uk!Geoffcs4g6ag@maccs.dcss.mcmaster.ca (Stephen M. Dunn) (09/16/89)
In article <411@castle.ed.ac.uk> erck12@castle.ed.ac.uk (Gnome) writes: $In article <1219@marlin.NOSC.MIL> jbjones@marlin.nosc.mil.UUCP (John B. Jones) writes: $-What is protected mode? Is there an unprotected mode? It sounds like $-some programming term, but what's it for? $-Thanks in advance for turning some lights on. $ As far as I know (and most of this knowledge is 2nd hand) the 80286 can $operate in two modes, protected and unprotected. The former of these is the real $80286, while the latter, which is used by DOS, makes it act like a 8086/88. The $term protected comes from the protected memory scheme available in that mode. The 286 does in fact have two modes - "real" mode (which makes it behave like an 8086/8088 and is used under DOS on AT-class machines) and "protected" mode, which provides the memory support for multi-tasking. This mode, as pointed out by "Gnome", provides the hardware support for protecting one process' private memory from other processes; this protection is pretty well necessary in order to implement a good multi-tasking OS. $This is needed by multi-tasking operating systems to stop one process $corrupting anothers memory. OS2 uses protected mode, except when the DOS box is $active. Yup. The 286 provides four levels of privilege, with (of course) the pro- vision of a method of switching between them. Generally, OS/2 applications run in the lowest mode, while the various components of the operating system itself run in the other modes. Anyone who has taken a university "introduction to operating systems" course will be familiar with the fundamentals of this. $If you think all this is complicated the 80386 has four modes! It has $the two suported by the 80286, true 80386 mode, and multi-8086 mode (which $simulates an individual 8086 in each 1M of the memory map - nice!). I hope the $lights are at least glowing now. This is one of the great problems with OS/2 - the 386 has the ability to multi-task DOS applications, but the 286 doesn't. Since OS/2 assumes it has a 286 (and runs a 386 in 286 protected mode), DOS applications will either run in the foreground or not at all. BTW, those who are familiar with DOS 4 will have seen in the manual a nifty little driver that uses extended memory (that memory outside the 0-640K range) to actually be expanded memory on 386 systems. This driver uses the advanced memory-mapping ability of the 386 to actualy make this memory appear to be in the 8086's 0-1M addressing range (as opposed to programs like PC magazine's EMM40.SYS, which uses extended memory to emulate expanded; this program assumes that you are running on a 286 and actually eats up 64K of your conventional mem- ory, because what it does it copies the data between conventional and extended memory each time you do a page swap ... this will make sense to EMS programmers and will probably sound like complete gibberish to others - write me if you'd like a few more details) -- Stephen M. Dunn cs4g6ag@maccs.McMaster.CA ********************************************************************** <std_disclaimer.h> = "\nI'm only an undergraduate!!!\n"; "VM is like an orgasm: the less you have to fake, the better." - S.C.