minar@reed.bitnet (Nelson Minar,(???)) (07/05/90)
What exactly is 286 protected mode? Where can I read about programming it? Specifically, I am interested in how it handles addresses. I'm aware it can access memory greater than 1MB, so I presume it handles segmenting differently. What does it do? I also understand that MS-DOS doesn't function in protected mode. Does the BIOS? Are there MS-DOS like OSs that will work in protected mode? Thanks for helping an ignorant..
austing@Apple.COM (Glenn L. Austin) (07/06/90)
minar@reed.bitnet (Nelson Minar,(???)) writes: >What exactly is 286 protected mode? Where can I read about programming it? >Specifically, I am interested in how it handles addresses. I'm aware it can >access memory greater than 1MB, so I presume it handles segmenting differently. >What does it do? >I also understand that MS-DOS doesn't function in protected mode. Does the >BIOS? Are there MS-DOS like OSs that will work in protected mode? 286 protected mode is the mode that OS/2 runs in. Almost any good '286 manual will talk about some of the differences, but the major one is that the segment registers are now really "selector" registers, with the selector table stored off in protected RAM. Some of the BIOS will work in protected mode, however, don't plan on using too much of it. A good portion of it assumes that the interrupt vectors are in segment 0, BIOS variables are in segment $40, the screen is at $Bx00, etc. This is not necessarily true in protected mode, since sequential segments are not necessarily sequential in memory. -- ----------------------------------------------------------------------------- | Glenn L. Austin | "Turn too soon, run out of room, | | Auto Racing Enthusiast and | Turn too late, much better fate" | | Communications Toolbox Hacker | - Jim Russell Racing School Instructors | | Apple Computer, Inc. | "Drive slower, race faster" - D. Waltrip | | Internet: austing@apple.com |-------------------------------------------| | AppleLink: AUSTIN.GLENN | All opinions stated above are mine -- | | Bellnet: (408) 974-0876 | who else would want them? | -----------------------------------------------------------------------------
bpendlet@bambam.UUCP (Bob Pendleton) (07/07/90)
From article <15154@reed.UUCP>, by minar@reed.bitnet (Nelson Minar,(???)): > What exactly is 286 protected mode? ... > I also understand that MS-DOS doesn't function in protected mode. Does the > BIOS? Are there MS-DOS like OSs that will work in protected mode? Ray Duncan has a new book out entitled "Extending DOS." Pick up a copy. It gives a good overview of the answers to all you questions and points you at sources for more detailled answers. But the basic answer is that in protected mode a segement value is actually a pointer into a table of 24 bit pointers. (Grossly over simplified!) And there are things called DOS extenders that let you program in protected mode and still use DOS. Read the book. It's a good place to start. Bob P. -- Bob Pendleton, speaking only for myself. UUCP Address: decwrl!esunix!bpendlet or utah-cs!esunix!bpendlet X: Tools, not rules.