Video

The following settings control screen I/O operations within a VDM.

VIDEO_FASTPASTE

Function:

Speeds up input from other sources than the keyboard.

Improves the speed of paste operations from the clipboard to a DOS application.

Does not work with all applications (in particular, some applications which monitor keyboard interrupts directly may experience errors).

Off.

At any time. This facilitates easy experimentation by the user.

Pasting into the DOS command prompt, or any application using DOS Console I/O functions, will generally work. However, the Microsoft Editor (M) and its successor, Programmer's Workbench (PWB), can fail when using fast pasting because they rebuffer keystrokes in an internal buffer, which can overflow.

VIDEO_MODE_RESTRICTION

Function:

Extends the 640KB DOS address space by limiting video mode support.

For text-based or CGA graphics based applications, the video memory normally reserved just above 640KB for high-resolution graphics modes can be remapped to conventional memory, providing an additional 64KB (or 96KB, depending on graphics mode) for DOS applications, TSRs, and other programs. This is valuable for applications that do not take advantage of EMS or XMS memory extenders.

It is not possible to completely hide the fact that the video adapter is high-resolution graphics-capable; some applications may attempt to enable those modes and use the memory above 640KB as video memory, inadvertently corrupting application data. Care must therefore be taken when using this feature.

NONE. The complete list of settings is:

None

CGA modes only (adds 96KB)

MONO modes only (adds 64KB).
Settable:
At VDM creation only.
Examples:
None.

VIDEO_ONDEMAND_MEMORY

Function:

Reduces swap space requirements for fullscreen VDMs.
Advantages:
Allows a full-screen VDM to run without pre-allocating a virtual video buffer for the worst-case video modes (high-resolution graphics modes). Using this setting does not prevent execution of graphics applications; it simply means that allocation of the buffer is delayed until it is needed. This can save a substantial amount of memory/swap space, which might be important under certain low-memory conditions. It also enables you to start a program quickly.
Drawbacks:
If allocation of a virtual video buffer for a full-screen VDM fails at the time the application changes video modes, the session must be frozen and switched back to the shell. Unless the user is able to free memory from another session, he may be unable to get the DOS application running again. This is a concern if the application contains unsaved data.
Default:
Off.
Settable:
At any time. This allows the user to save memory the next time the session is switched to full-screen.
Examples:
None.

VIDEO_RETRACE_EMULATION

Function:

Simulates the video retrace status port to provide faster access.
Advantages:
DOS applications that poll the video retrace status port often write to the screen only during the retrace interval, even though it is safe (on EGA and VGA adapters) to draw at any time without causing interference (also known as "snow"). This feature causes most applications to write to the screen more often, and compensates for the performance drag imposed by monitoring the port in the first place.
Drawbacks:
Some applications may poll the port in such a way that overall performance is worse; this is sometimes true of applications that draw only during vertical (not horizontal) retrace. Unfortunately, while turning off trace emulation will restore performance, there is a risk that screen-switching will not be as reliable.
Default:
On. Reliable screen-switching has higher priority over the minority of applications that will experience some drag in performance.
Settable:
At any time. This allows the user to experiment with different settings in the event of a performance problem.
Examples:
None.

VIDEO_ROM_EMULATION

Function:

Emulates selected INT 10h ROM Video functions.
Advantages:
Provides faster output for selected video functions than ROM services typically provide. This also has a dramatic effect on the performance of those functions in a window.
Drawbacks:
Some ROMs may offer enhanced services that are not included in the emulation. Applications which rely upon these services may not execute correctly.
Default:
On. Because the INT 10h ROM Video services are well-documented, incompatibilities are unlikely and the performance benefits of using the emulation are quite significant.
Settable:
At any time. This allows the user to experiment in the event of a compatibility problem.
Examples:
None.

VIDEO_SWITCH_NOTIFICATION

Function:

Notifies a DOS application of a switch to/from full-screen mode.
Advantages:
Allows applications that monitor this notification to redraw their screens as needed. This may be necessary for some video adapters that provide modes (and applications that use those modes) which are not fully supported by the OS/2 video driver or which are slightly incompatible. It is also valuable in situations where an OS/2 video driver has not allocated a virtual video buffer (see VIDEO_8514_XGA_IOTRAP below). Use this setting if you use the VIDEO_ONDEMAND_MEMORY DOS setting, because concurrent buffer allocation and screen switching can make a screen go black.
Drawbacks:
When used indiscriminately, this feature may cause unnecessary and time-consuming screen redrawing. For standard MONO/CGA/EGA/VGA video modes, the OS/2 video driver should be able to restore application screens without assistance.
Default:
Off. For standard hardware and standard video modes, this feature is not necessary.
Settable:
At any time. This allows the user to experiment in the event of a compatibility problem.
Examples:
Windows 2.x and 3.x understand this notification and will redraw themselves accordingly. For WIN-OS/2 sessions, set this setting on.

VIDEO_WINDOW_REFRESH

Function:

Adjusts the window update frequency for a given VDM.
Advantages:
For applications (particularly graphics) that write frequently to video memory, this value can be increased to reduce time spent updating the window and provide more processor time for the application.

Note: This has no effect on updates based on other events such as keyboard input or synchronous scrolling operations or any video events other than refresh.

Drawbacks:
A large refresh period can make an application unusable (or at least, very hard to use).
Default:
0.1 seconds. This has been found to yield the best overall performance.
Settable:
At any time, in increments of 0.1 seconds. This allows for experimentation. The range is from 0.1 to 60.0 seconds.
Examples:
This setting affects normal TTY-style output. Compare a DIR or TYPE operation before and after altering this setting.

VIDEO_8514_XGA_IOTRAP

Function:

When set OFF, unrestricted access to 8514/A display adapter hardware. Note that this setting is only available for systems with 8514/A display adapters installed.
Advantages:
Achieves higher performance for 8514/A applications and eliminates the overhead of the 1MB 8514/A virtual video buffer normally allocated for each VDM when set OFF.
Drawbacks:
Screen-switching away from the application will result in immediate freezing of the application, and the system may not be able to reliably switch back; that is, the screen image may not be correct. This may be overcome by setting VIDEO_SWITCH_NOTIFICATION on, which notifies applications to redraw their own screen images. Note however, that not all applications will take advantage of the notification.

Note: An application with this setting enabled may not be run in windowed mode, or copied to the clipboard, because there is no complete information about its state.

Default:
Off.
Settable:
At VDM creation only.
Examples:
When executing Windows 3.0 with the 8514/A display driver, certain operations such as painting dithered backgrounds will run significantly faster.

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