Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!uunet!rosevax!marknew From: marknew@rosevax.Rosemount.COM (Mark Newman) Newsgroups: comp.sys.ibm.pc Subject: Brain-dead 286 - summary Message-ID: <8681@rosevax.Rosemount.COM> Date: 6 Mar 90 13:14:13 GMT Reply-To: marknew@rosevax.UUCP (Mark Newman) Distribution: usa Organization: Rosemount Inc., Eden Prairie, MN Lines: 139 Last week I posted a message asking what was wrong with the '286. A number of people were kind enough to respond with some useful infor- mation and opinions, and several asked that I post a summary. Well, here it is. I edited some of the responses to keep the length of the summary reasonable. -Mark Newman marknew@rosevax.rosemount.com ======================================================================== From Raymond Chen (raymond@math.berkeley.edu): There is no way to switch from protceted mode to real mode on a 286. The way it's done in practise is [1] save away the information you want to preserve, [2] set a flag to say "I am doing something goofy", [3] tell the keyboard chip to send a reset signal, [4] then halt the processor. Then when the reset signal comes (after a few milli- seconds), [5] the chip restarts in real mode, [6] notices the "I am doing something goofy" flag, [7] loads the context from the stuff you saved away in step [1] and continues. Gordon Letwin has called it "Stopping the car in order to change gears." - - - From Dean William Wallwey (wallwey@snoopy.colorado.edu): You definitely want to get a 386SX. I have a 286, and I am very soon going to upgrade my mother board to a 386SX because 286's are going to be left behind. There are a lot of reasons to buy the 386SX. The 386 and 386SX both have very powerful memory mapping powers which are used by the new operating systems. They also both have what INTEL calls Virtual 86 mode so you can multitask DOS programs using Windows or DesqView for the 386. The small amount of money you save by buying a 286 machine will come back to haunt you tommorrow, even if you use it at home. The new software that is coming around the bend really needs large flat memory spaces (EVEN the NEW 386 version of OS/2 later this year will take advantage of the 386's powers and really shine!) Some background info: The 386SX is identical to the 386 from a software point of view. The 386SX uses a 16 bit bus whereas the 386 uses a 32 bus so the 386 is a little faster at the same speed because the 386SX has to reference memory twice for a 386's every one. Both the 386 and 386SX microprocessors are 32 bits internally and act exaxctly the same. The 286 is a 16 bit bus and a 16 bit architecture. It does not have the powerful memory managment facilities of the 386. The 286 is *BRAIN DEAD* compared with 386 and 486 computers. The 386,386SX and 486 will run OS/2, mulitasking DOS, and UNIX, MUCH MUCH better than the 286 ever will. Even the new Windowing word processors from MicroSoft (WORD for WINDOWS already out) and the future WordPerfect for OS/2 will run so much better on a 386/386SX than the 286. Even if you don't think that you'll need the power of the 386 group, you will soon see even the simple "home" programs like word pro- cessing and spreadsheets longing for the 386/386SX. (I guess they already do with WORD for WINDOWS, and Lotus 1-2-3 ver 3.0 even though they will "run" on a 286). - - - From Michael D. Kersenbrock (michaelk@copper.WR.TEK.COM): The 286 is brain dead primarily because Intel made two major errors in it's design: 1.) In protected mode (where it can access more than 1 Megabyte), the chip's MMU-ish architecture is "different" to the point that DOS can't handle it. DOS MUST run in "real" mode (1Meg addressablity only). When running DOS, protected mode IS entered sometimes, but interrupts have to be turned off during the time it is in protected mode. 2.) Given #1 above: when protected mode is entered, Intel provides NO way to go BACK to real mode. Because real mode is the mode that the chip powers up in, what an AT does to return into REAL mode is to have itself hardware-reset (by the keyboard controller I think) then, "recover" from where it left off. Pretty wild. So, it's not brain dead in the sense of being useless, but brain dead in the sense that it isn't what it could/should have been had things been done just a little bit different. BTW - I just traded some stuff for a used 12-Mhz AT backplane, I hope to get it running this week (I've a Turbo-XT clone). Even with a brain dead processor, it should run two or three times faster than my old PC.... BTW#2- Actually my old 10Mhz XT clone is adequate for home use (given also that it has 3Meg of EMS 4.0 memory that helps it a LOT). - - - From Marc Louis Levinson (gt0159a@prism.gatech.edu): The 286 is not really brain dead. The problem is that nobody has ever properly taken advantage of its capabilities. The chip has available what is called protected mode, which allows advanced memory handling and multitasking. Chances are slim that you can ever find a useful DOS application to use this mode. OS/2, UNIX and some Network software use 286 protected mode. The 386 and 386sx can use advanced memory handling for normal DOS. Overall, the 386 series has faster throughput. If you are not planning to use hi power applications, like LOTUS 3, Windows [loaded to the max], Autocad and others to maximum perform- ance abilities, then a 286 is ok. Realize that much of the software now being developed will not run on a 286 but will run on an sx. Con- sider the lifetime of your computer before you buy one. - - - From Dick O'Connor (djo7613@blake.u.washington.edu): There's nothing wrong with the '286. You should see the programs my wife and I did for the kids, for household organization, for gardening, for the church, on and on with an 8 MHz XT-compatible, and our new 286 machine screams thru all of them. No way we need a 386 for home use, and few people at my office need them either. I can't speak for all of the mags, who have a vested interest in pleasing Intel, but I personally feel Bill Machrone and the editorial staff of PC Magazine are for the most part the most arrogant bunch of trend-setter-wanna-be's I've ever had the agony of reading. They care not for the actual uses of the individual, but only for unlimited desktop power. And those dudes use their machines for word pro- cessing! What a laugh... Well, I shouldn't lump them all in the same boat. Machrone is arrogant, but Seymour is right about half the time, Dvorak *knows* he's trying to needle you, so I can take him, Manes is funny, and Zachmann has just guessed wrong in a BIG way about OS/2. Then again, they could all be the prophets of a new age, and I could be dead wrong! - - - From John Limpert (johnl@n3dmc.UU.NET): The 80286 cannot deal with numbers larger than 16 bits or data larger than 64K bytes without doing it in ugly, slow and error prone soft- software. The 80386 can work with 32 bit numbers and 4 gigabyte data areas (with the right operating system and software). Many programs were designed for 32 bit machine like the 80386 and if they will run at all on the 80286 (and many wont), they operate very slowly. Don't buy an 80286 machine, you will be wasting your money. In the future there will be a lot of software that will only be available for 80386 class machines. I am writing this on the 80286 UNIX system I bought several years ago. I wouldn't throw it out but I wouldn't buy another one today.