OS/2 FAQ List: User's Edition (4 Apr 94)

(1.3) DOS and Windows Compatibility

How good is OS/2 2.1's DOS and Windows compatibility?

OS/2 1.x [See (1.2) Differences Between Versions] justifiably earned a 
reputation for poor DOS compatibility.  Since it was hampered by the 
80286, it could not run more than one DOS application at a time.

The situation changed dramatically with OS/2 2.0, and Version 2.1 adds 
further refinements.  Version 2.1 preemptively multitasks DOS and Windows 
(standard and enhanced mode) applications in separate, protected sessions, 
without purchasing either environment.

OS/2 2.1 provides a complete DOS emulation equivalent to DOS 5.0.  The 
operating system can provide each DOS application with up to 32 MB of EMS 
4.0 (expanded memory), 16 MB of XMS 2.0 (extended memory), and/or 512 MB 
of DPMI 0.95 (DOS Protected Mode Interface extended memory), all from its 
pool of physical and/or virtual memory (meaning you do not have to have as 
much RAM in your system as your applications request).  These limits are 
in addition to the up to 730K free conventional memory supplied to each 
DOS application, even after mouse and network drivers [See (3.8) 
Networking Products] are loaded.  As in DOS 5.0, DOS code and device 
drivers may be loaded into high memory.  A 386 memory manager like QEMM is 
not needed -- these features are provided by OS/2 2.1 directly.

The DOS emulation allows customization of device driver sets -- each DOS 
application shares a systemwide CONFIG.SYS and the equivalent of its own 
CONFIG.SYS. Also, there is a systemwide AUTOEXEC.BAT file; however, batch 
commands particular to each DOS application can be invoked using separate, 
application-specific AUTOEXEC.BAT files.  And many DOS Settings are 
provided to fine tune [See (5.6) Performance Tuning] each DOS/Windows 
application's behavior (e.g. IDLE_SENSITIVITY).  Most of the popular 
DOS/Windows applications on your hard disk will be migrated automatically 
when you install OS/2 2.1.

In addition, OS/2 2.1 will boot one or more specific versions of DOS in 
separate sessions, to assist in running particularly difficult 
applications (e.g. DOS networks, MSCDEX and CD-ROM drivers).  So, for 
example, it is possible to multitask DOS 3.3, DOS 4.0, DOS 5.0, DOS 6.0, 
DOS 6.2, DR-DOS, emulated DOS, and Desqview running atop DOS, all in 
separate sessions, either windowed or full screen, all with the same 
and/or separate device drivers, TSRs, environment variables, etc.  DOS 
boot images may be stored on a hard disk.  These procedures are described 
in the online Command Reference (under VMDISK), Master Help Index, and in 
the Installation Guide (Appendix E).  [See also (5.9) Specific DOS 
Sessions.]

Standard graphics modes [generally up to the resolution of the desktop; 
See (2.2) SuperVGA Support] are supported in DOS windows, as are 
selectable text mode fonts.  Cut/paste to/from windowed DOS applications 
is supported (to/from other DOS, OS/2, and Windows applications), 
including graphics cut/paste.  Theoretically, OS/2 2.1 can run up to 240 
simultaneous DOS/Windows sessions; the practical maximum depends on system 
resources.

OS/2 2.1 will, in fact, run virtually all DOS applications in existence, 
including notorious ones such as Microsoft Flight Simulator, Wing 
Commander, Maple, MatLab (Version 3.5k or later), AutoCAD (Release 12 
requires maintenance version C2 or later), and others.  Those that do not 
run generally fall into the following categories:

  1. Programs that use Virtual Control Program Interface (VCPI) memory 
     extenders or other extenders which require direct access to 80386 
     control registers.  Since such applications are also all but 
     incompatible with Windows, most vendors have updates for DPMI 
     compatibility;

  2. Applications which attempt to directly address the physical sectors 
     of an OS/2 managed nonremoveable hard disk drive.  Such programs 
     include UnErase in Norton Utilities [See (3.4) Disk Utilities]. 
      Fortunately OS/2 2.1 has a built-in UnDelete feature which is more 
     robust than Norton's approach.  (Consult the online Command Reference 
     for information on how to enable UNDELETE);

  3. Timing sensitive DOS applications.  Certain DOS programs that 
     generate digitized sound through the PC's internal speaker may have 
     distorted sound.  High speed, real time data collection may be 
     compromised.  These problems can often be minimized or even 
     eliminated using OS/2 2.1's DOS Settings.

  4. Certain DOS programming debuggers.  DOS applications running under 
     OS/2 2.1 are not permitted to access debug registers DR0-DR7 from a 
     DOS session.  Also, DOS debuggers will not be able to set hardware 
     breakpoints, and all read/write operations to debug registers in 
     virtual 8086 mode will be ignored.

 See (3.12) Backup Software for information on OS/2 backup issues.

 DOS-based disk caching software is not required since OS/2 includes a 
 built-in, highly configurable, efficient disk cache.  Also, the OS/2 
 CD-ROM file system's cache may be adjusted; see the online Command 
 Reference for details.

 DOS programs running under OS/2 2.1 are extremely fast.  A single DOS 
 application (no other applications open) running full screen under OS/2 
 2.1 typically achieves 95-97% of the performance it would have under 
 native DOS.  If the DOS application performs any disk I/O it can actually 
 operate up to several times faster than it would if running under native 
 DOS.

 If pure DOS is absolutely required, OS/2 2.1 includes a utility called 
 the Boot Manager.  The Boot Manager can provide a listing of all the 
 operating systems available on the system and will allow selection of any 
 one at startup, with a default after timeout.  The OS/2 DualBoot method 
 (to switch between DOS and OS/2 only) is still available as well. 
  Consult the Installation Guide for instructions on how to use Boot 
 Manager or DualBoot.  Note that OS/2 2.1 need not be installed on Drive 
 C -- it can reside on other volumes [See (4.3) Hard Disk Partitioning].

 Compatibility with Windows, a popular DOS extender, is provided by 
 Win-OS/2, an environment based on Microsoft's Windows source code.  It 
 runs Windows 3.x enhanced mode and standard mode applications under OS/2 
 2.1, either on a full screen Windows desktop (with the familiar Program 
 Manager and one or more Windows applications) or "seamlessly," alongside 
 OS/2 applications on the Workplace Shell desktop.  "Seamless" operation 
 is available in VGA, many SuperVGA, 8514/A, and XGA resolutions with OS/2 
 2.1 as it ships.  [See (2.2) SuperVGA Support.]

 Several icon conversion utilities can convert Windows icons for use by 
 the OS/2 Icon Editor and/or OS/2-specific programs [See (3.2) Shareware 
 and Freeware Sources].  (No conversion is necessary if the icons are to 
 be used with Windows programs running under OS/2 2.1.)

 OS/2 2.1 directly provides all Windows enhanced mode features save one: 
 support for Windows virtual drivers (VxD).  Only two major applications 
 are affected: MathCAD 4.0 or 5.0 and Microsoft Visual C++.  {{ (It is 
 possible to use command line compile options with Visual C++ running 
 under OS/2.) }}  Services provided by WINMEM32.DLL are supported.

 Windows applications are well integrated into the overall OS/2 Workplace 
 Shell environment with DDE and Clipboard hooks, and OLE (Object Linking 
 and Embedding) is supported among Windows applications.  Adobe Type 
 Manager [See (5.5) Adobe Type Manager] and TrueType for Win-OS/2 comes 
 with OS/2 2.1.  Windows screen (for a full screen desktop) and printer 
 device drivers will work under Win-OS/2 [See (2.2) SuperVGA Support]. 
  Such notorious Windows applications as Word, Norton Desktop (save 
 portions described above), Toolbook, and After Dark work fine under 
 Win-OS/2.  Even applications which rely on the Windows Multimedia 
 Extensions (supplied as part of Win-OS/2) operate without trouble.  [See 
 (3.6) Multimedia for information on the OS/2 multimedia extensions, 
 MMPM/2.]  All the Windows applets (except those made redundant by OS/2's 
 applets) are provided.

 Win-OS/2 departs from Microsoft Windows in that it allows more than one 
 Windows desktop and can preemptively (rather than cooperatively) 
 multitask Windows applications in separate, robust, protected sessions, 
 at the user's option.  Also, both DOS and OS/2 applications can be 
 started from the Win-OS/2 Program Manager.

 Some Windows applications require custom settings in WIN.INI.  If such a 
 Windows application has been installed under the DOS version of Windows, 
 Win-OS/2 may not be able to find the appropriate files or configuration. 
  Try reinstalling the Windows application under Win-OS/2.  (Note that 
 several options are available for Win-OS/2 interaction with the Windows 
 INI files.  For example, the Windows INI files may be migrated during 
 installation.  Or both Win-OS/2 and Windows can share a single set of INI 
 files.)

 In short, OS/2 2.1 is generally regarded as the most DOS and Windows 
 compatible among the new crop of 32-bit operating systems (NT included). 
  It is also generally regarded as a better DOS multitasker than Desqview.

 Related information:

 (1.2)  Differences Between Versions 
 (2.2)  SuperVGA Support 
 (3.2)  Shareware and Freeware Sources 
 (3.4)  Disk Utilities 
 (3.6)  Multimedia
 (3.8)  Networking Products 
 (3.12) Backup Software 
 (4.3)  Hard Disk Partitioning 
 (4.4)  Starting OS/2 from Diskette 
 (5.5)  Adobe Type Manager 
 (5.6)  Performance Tuning 
 (5.9)  Specific DOS Sessions

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