Standard Mode: The normal operating mode for running Windows. This mode provides access to extended memory and also lets you switch among non-Windows applications.
Standard mode uses the 80286 processor's protected mode to provide direct access for Windows and Windows applications to up to 16MB of extended memory. Expanded memory for DOS applications is only supported with physical expanded memory cards (emulation of expanded memory using extended memory is not supported).
Standard mode requires an 80286 processor or above, and at least 1MB of installed memory, with a minimum 192KB of free extended memory. The XMS driver HIMEM.SYS must also be loaded. Windows applications must be written to comply with the memory management rules for Windows 3.0 in order to run in standard mode.
Standard mode is recommended by Microsoft when running only Windows applications (that is, no DOS applications) in certain configurations, even on an 80386 machine. In the Windows 3.0 manual, on page 429, it is suggested that users running only Windows 3.0 applications should run in standard mode, even on 80386 systems with 2-3MB of memory, as there is a performance improvement in doing so.
Standard mode is necessary for some Windows applications (for example, Microsoft Excel** Version 3.0). To accommodate such applications, OS/2 Version 2.0 must provide additional support. Basically, these applications need to access DPMI services for extended memory support, which is available under Windows 3.0 when running in standard or enhanced modes. See DOS Protected Mode Interface for further information on DPMI support under OS/2 Version 2.0.
The other requirement is to supply Windows services to Windows applications. This service is provided in OS/2 Version 2.0 by modifying the Windows kernel and running it in standard mode in a VDM. As part of the joint development and cross-licensing agreement between IBM and Microsoft, IBM has access to the Windows source code. IBM has modified the source to provide a Windows kernel (WIN-OS/2) capable of running as a DPMI client within a VDM (the retail version of Windows 3.0 can only function as a DPMI host), and includes this kernel as part of the OS/2 Version 2.0 product.
OS/2 therefore supports Windows applications running in standard mode in a VDM. Use of the VDM design, which provides a self-contained DOS environment, means that the environment is identical, from the application's point of view, to running under Windows loaded in standard mode, on DOS. This design therefore provides the maximum compatibility with the DOS/Windows environment. In fact, it offers a wider range of compatibility, since Windows 2.x applications, which require real mode operation under Windows 3.0 in DOS, can be run concurrently with Windows 3.0 applications running in standard mode. This combination is not possible at the same time under DOS/Windows 3.0.