3 ms·
This is a good point. But there’s a nuance in that OS/2 1.x used 286 protected mode the way Intel had intended it, by booting into it and never returning to rea
by pavlov 3y ago
This is a good point. But there’s a nuance in that OS/2 1.x used 286 protected mode the way Intel had intended it, by booting into it and never returning to real mode (which was supposed to be impossible).
Whereas Windows 3.0 was a so-called DOS extender: it switched to protected mode for an application but could also come back. That kind of execution model wasn’t envisaged in 1985 when the OS/2 project started.
Steven Sinofsky writes about it in his personal Microsoft history:
’DanN shared with me what he was most excited about—one of the key “secrets” of Windows 3, which was how the product enabled protected mode but could also remain compatible with old MS-DOS programs. David Weise (DavidW) and Murray Sargent (MurrayS) had invented some novel uses of the Intel chipset that even Intel did not anticipate, which enabled these efforts. One programming trick called PrestoChangeoSelector was a key “hack” they developed and later became an absurd symbol of “secret” application programmable interfaces (APIs) in Windows (absurd, because it was supposedly secret, when in fact it was right there to see). Dan told this story with great Microsoft pride, as the development of Windows 3 and these techniques represented much of what Microsoft did so well in those days. Hack.’
https://hardcoresoftware.learningbyshipping.com/p/003-klunder-college https://hardcoresoftware.learningbyshipping.com/p/003-klunde...
- mschaef 3y ago> But there’s a nuance in that OS/2 1.x used 286 protected mode the way Intel had intended it, by booting into it and never returning to real mode ( OS/2 had the ability to run DOS programs in a DOS box. my recollection was that OS/2 had to switch back to real mode to do this (thereby suspending all the OS/2 native processes.) Windows 3.0 in standard (286) mode did something similar. All this was done with triple faulting, iirc: http://www.rcollins.org/Productivity/TripleFault.html http://www.rcollins.org/Productivity/TripleFault.html > Steven Sinofsky writes about it in his personal Microsoft history: You might like Larry Osterman's recollection of this, if you haven't already seen it: https://www.landley.net/history/mirror/ms/davidweise.html https://www.landley.net/history/mirror/ms/davidweise.html
- rep_lodsb 3y agoOS/2 1.x did switch from protected back to real mode by resetting the CPU, in order to run a single DOS application in the "penalty box". Device drivers even had to be able to run seamlessly in both modes! That article is paywalled, but what you quoted reads like pure bullshit. PrestoChangoSelector was used in protected mode to make code segments writable, and had nothing to do with DOS compatibility: https://jeffpar.github.io/kbarchive/kb/089/Q89560/ https://jeffpar.github.io/kbarchive/kb/089/Q89560/