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OSDASET - DOS SETTINGS & DESCRIPTIONS FOR AN OS/2 DESKTOP ICON
12/16/94
================================================================
DOS SETTINGS FOR AN OS/2 DESKTOP ICON
================================================================
STANDARD DOS SETTINGS
---------------------
This document describes the Standard DOS Settings in an OS/2
Virtual DOS Machine (VDM).
Depending on hardware configuration, and software level, some
of these settings may not exist.
AUDIO_ADAPTER_SHARING
Function: Allows access to audio hardware for the DOS
session. Two applications cannot use an audio
adapter even if one is not required to run the
program. This will allow you to minimize conflicts
by defining audio specifications for each DOS
session.
Select Optional to indicate that a program in this
DOS sesion should use an audio adapter if one is
available.
Select Required to indicate that a program in this
DOS session must have access to an audio adapter.
Select None to indicate that a program in this DOS
session does not require an audio adapter.
Default: None.
Settable: At any time.
COM_DIRECT_ACCESS
Function: When set on, VCOM.SYS allows direct access to
the COM ports.
Advantages:Programs that need direct access like AS/400
Asynch Router, FastLynx, FSDUAT, and MS Word will
now work.
Drawbacks: Buffers in COM.SYS can not be used. Characters
may be lost and some applications may suffer from
the lack of buffering.
Default: Off.
Settable: At VDM creation only.
COM_HOLD
Function: When set on, provides exclusive access to COM
ports for the specified VDM, preventing other
processes from using the port and preventing the
operating system from releasing the port until
the VDM terminates.
Advantages:For certain applications that use COM ports and
require multiple programs to access the COM
port (for example, this setting prevents the
COM port from being released when the first
program ends).
Drawbacks: If not required by the application running in a
VDM, this setting may prevent their applications
from accessing COM ports.
Default: Off.
Settable: At VDM creation only.
Examples: Certain bulletin board applications use one
program to dial the BBS and another to exchange
information; setting COM_HOLD on prevents the
operating system from releasing the COM port when
the first program ends.
COM_RECEIVE_BUFFER_FLUSH
Function: Allows control of the received data buffers
when the DOS session is switched to the
foreground, or when the DOS program enables
the received data interrupt.
Select Receive Data Interrupt Enable to indicate
that, for this DOS session, the operating system
is to discard data in the received data buffer
when the DOS program enables the received data
interrupt.
Select Switch to Foreground to indicate, for
this DOS session, the operating system is to
discard data in the received data buffer when the
DOS program is switched to the foreground.
Select ALL to indicate that communications data be
discarded when a DOS program enables the received
data interrupt or the program is switched to the
foreground.
Select NONE to indicate, for this DOS session,
the operating system is to keep data in the
received data buffer.
Default: None.
Settable: At VDM creation only.
COM_SELECT
Function: When set, allows a program to select and use one
communication port.
Advantages:You can limit your program to just the COM port
that it requires, some programs like Laplink pro
try to take over every available COM port.
Communications that are not selected are hidden
from the program.
Drawbacks: Some programs need to have access to the COM
ports to work, even if they are not using them.
Default: All (Full access to the COM ports.)
Settable: At VDM creation only.
DOS_AUTOEXEC
Function: To specify a different batch file other than
the default AUTOEXEC.BAT.
Advantages:Different batch files could be specified for
different DOS programs.
Default: AUTOEXEC.BAT in root directory.
Example: A new batch file which contains some SET
statements relative to an individual program, can
be kept separately .
Settable: At VDM creation only.
DOS_BACKGROUND_EXECUTION
Function: When set off, suspends execution of the program
when it is in the background.
Advantages:Many DOS applications are written on the
assumption that they are single tasking and
all the resources of the work station
can be monopolized. It is not uncommon for a
program to continually poll for keyboard input
(Examples are WordPerfect 5.1 and Lotus 1-2-3
R2.2). In a multitasking environment, this can
impact system performance, especially when more
than one such program is running. Turning the
DOS application off when its virtual DOS
machine is in the background reduces its
demands on the system.
Also see IDLE_SENSITIVITY and IDLE_SECONDS.
Drawbacks: Communications programs fail if background
execution is turned off, also DDE for Windows
applications. Try changing the values of
IDLE_SECONDS and IDLE_SENSITIVITY before turning
DOS_BACKGROUND_EXECUTION off.
Default: On (Background execution is enabled).
Settable: At any time.
Examples: If more than two DOS programs are running and
tuning with IDLE_SENSITIVITY and IDLE_SECONDS
does not provide sufficient improvement, turn
DOS_BACKGROUND_EXECUTION off for the least used
application.
DOS_BREAK
Function: Enables or disables Ctrl+Break for the
specified VDM. Also check for the BREAK statement
in the CONFIG.SYS. Set BREAK=ON in the CONFIG.SYS
to make Ctrl+Break and Ctrl+C working in addition
to setting DOS_BREAK on.
Advantages:Enables a DOS application running in the
VDM to be interrupted using the Ctrl+Break or
Ctrl+C key sequences.
Drawbacks: This setting is useful only if an application
must be quickly interrupted; you can end
a VDM by closing it from the Window List.
Default: Off (Ctrl+Break is disabled).
Settable: At VDM creation only.
Examples: If you want interrupt a DOS batch file
running in a virtual DOS machine, this setting
should be turned on.
DOS_DEVICE
Function: Use this setting to add or modify information
about DOS device drivers for the specified VDM, in
addition to the information specified in
CONFIG.SYS.
Default: When this setting is selected, a list is
appears with information about each DOS device
driver in the CONFIG.SYS. The information
consists of the path and file name of each DOS
device driver and its current parameters, if
applicable. For example:
C:\OS2\MDOS\ANSI.SYS
You can:
- Type the name of a DOS device driver to
add it. Typing should begin on a new line.
- Delete all the information about a device
driver to remove it.
- Type or delete to add, change, or delete a
value.
Settable: At VDM creation only.
Examples: A program to support hardware, such as a scanner,
may include a device driver needed only for
itself. The device driver should be loaded with
the DOS_DEVICE setting instead of in the
CONFIG.SYS.
DOS_FCBS
Function: Specifies the maximum number of file control
blocks (FCBs) that can be opened by applications
running in the VDM. Note that this setting
affects only those modules that use file-sharing.
Advantages:Reducing this setting may improve DOS application
performance in a resource-constrained
networking environment. When the maximum number
of FCBs is opened by an application, the least
recently used FCB is closed to allow additional
files to be opened; see DOS_FCBS_KEEP below.
Drawbacks: Reducing this setting to an excessively low
number may inhibit the performance of applications
that use large numbers of files. Check
application documentation for recommended FCB
settings.
Default: 16.
Settable: At VDM creation only.
Examples: None.
DOS_FCBS_KEEP
Function: Specifies the number of file control blocks,
FCB, protected against automatic closure.
Advantages:If this setting is specified as "n," the first
"n" files are protected against automatic
closure as described in "DOS_FCBS".
This may improve application performance.
Default: 8.
Settable: At VDM creation only.
Examples: None.
DOS_FILES
Function: Specifies the maximum number of file handles
that can be opened in a VDM.
Advantages:Setting this value higher than the default
may improve performance for applications
that use a large number of files. Check
application documentation for recommended
settings.
Drawbacks: Setting the number of file handles higher
than necessary reduces the available memory.
Default: 20.
Settable At any time.
Examples: DBASE IV requires a DOS_FILES setting of at least
40.
DOS_HIGH
Function: Determines whether DOS is loaded outside the
640KB low memory address space.
Advantages:Loading DOS into high memory allows more
available memory for application code and data
within the 640KB address space.
Drawbacks: Applications that require access to DOS
internal control structures require DOS to be
loaded into low memory, and so cannot use this
setting.
Default: Off (DOS is loaded into low memory).
Settable: At VDM creation only.
Examples: None.
DOS_LASTDRIVE
Function: Specifies the highest available logical drive
letter for the specified VDM. This setting is
similar to the LASTDRIVE= statement in a DOS
CONFIG.SYS.
Default: Z.
Settable: At VDM creation only.
Examples: Each additional drive letter uses about 100
bytes. Setting the LAST_DRIVE to a lower letter
such as J or K provides more conventional memory
for an application.
DOS_RMSIZE
Function: Specifies the DOS memory size. This is the
amount of memory available to DOS applications.
Advantages:The virtual video device driver uses this setting
on certain video adapters to set even more than
640KB.
Drawbacks: This setting is of little use to most users
as there is no point specifying less than 640KB.
Default: The default is 640KB.
Settable: At VDM creation only.
Examples: None.
DOS_SHELL
Function: To specify the DOS command processor, or to add
parameters to affect the command processor. This
points by default to COMMAND.COM. If you have
a different command processor, it should be
specified here.
Advantages:You can specify a command processor other than the
default COMMAND.COM, if required by a specialized
application, or may alter the environment space
available for the VDM.
Default: C:\OS2\MDOS\COMMAND.COM C:\OS2\MDOS /P
Settable: At VDM creation only.
DOS_STARTUP_DRIVE
Function: Specifies the location of the DOS kernel to be
loaded into the VDM.
Advantages:Allows specific versions of DOS to be loaded into
a VDM using the VMB facility, allowing the
execution of version-dependent DOS applications.
Drawbacks: Performance may not be as good as the VDM
kernel, that is optimized for the OS/2
environment.
Default: The DOS Emulation kernel is loaded.
Settable: At VDM creation only.
Examples: See Chapter 12, "Virtual Machine Boot."
DOS_UMB
Function: Specifies whether DOS owns Upper Memory
Blocks (UMBs) and manages the loading of device
drivers and TSR programs.
Advantages:Setting DOS_UMB on allows use of the DEVICEHIGH=
and LOADHIGH statements, to load device drivers
and TSR programs into Upper Memory Blocks, thereby
preserving space in low memory for use by
applications.
Drawbacks: Certain applications that make use of UMBs need
to access and manage the UMBs directly; such
applications do not run when DOS_UMB is set on,
because DOS owns the UMBs.
Default: Off (UMBs are owned by certain types of TSR
programs and DOS device drivers if necessary).
Settable: At VDM creation only.
Examples: None.
DOS_VERSION
Function: Allows the operating system to report a "fake"
DOS version number in response to a request from
a program in the VDM, to support applications
that check for a DOS version number.
Advantages: Allows some programs that do not start unless
they detect a prerequisite DOS version to run in
DOS Emulation.
Default: 20
Settable: Before application initiation.
Examples: Lotus 1-2-3 R3+ runs in DOS Emulation if it
is "fooled" into thinking that it is running
under DOS 3.3 by putting the following lines into
the DOS_Version list box:
- 123DOS.EXE,3,30,255
- 123.EXE,3,30,255
- LOTUS.EXE,3,30,255
DPMI_DOS_API
Function: Determines if DOS API translation is enabled for
the specified VDM.
Default: AUTO (API translation is enabled if required).
Settable: At VDM creation only.
Examples: None.
DPMI_MEMORY_LIMIT
Function: Specifies the maximum amount of protected
mode memory (in megabytes) available to DPMI
applications running in the VDM.
Advantages:For applications that require large amounts of
DPMI memory, this setting may be used to increase
the amount of available memory up to 512MB.
Default: 2MB.
Settable: At VDM creation only.
Examples: None.
DPMI_NETWORK_BUFF_SIZE
Function: Specifies the size, in kilobytes (KB), of
the network translation buffer for DPMI programs
in this session. The range is from 1 to 64 KB.
Default: 8KB.
Settable: At VDM creation only.
Examples: This setting allows you to configure the
size of the translation buffer for Windows
programs that transfer data over a network.
If a network-specific Windows program does
not run correctly under OS/2 V2.X increase
this setting, then restart the session.
EMS_FRAME_LOCATION
Function: This DOS setting allows you to change the
location of the LIM EMS region. LIM EMS uses a
64KB address region known as an EMS page frame,
through that programs can access expanded
memory. (This allows programs to use more than
640KB of memory.)
Advantages:If you have problems running a program that uses
both a hardware device and LIM EMS expanded
memory, the problem may be due to conflicting use
of addresses by LIM EMS and the hardware device.
If this occurs, first use the
EMS_HIGH_OS_MAP_REGION setting to set the extra
address region used by EMS to 0. This may solve
the problem. If the problem persists, the
EMS_FRAME_LOCATION setting can be used to select
64KB region that does not conflict with hardware.
You can choose where to place the frame from a
list of choices or can choose to have no EMS frame
for programs that do not require a frame. You can
also reduce the DOS Memory Size setting and place
the frame below 640KB.
Drawbacks: The best solution, when problems are due to
hardware conflicts, is to use the
MEM_EXCLUDE_REGIONS and MEM_INCLUDE_REGIONS
settings to specify the addresses that
the hardware uses rather than using this setting.
Default: The default AUTO setting leads to correct
choices of LIM EMS addresses. You may never need
to change his setting.
Settable: At VDM creation time only.
Examples: In some cases the default choice may conflict
with addresses used by hardware on the
machine. This can happen only for devices that
are not supported by a virtual device driver.
EMS_HIGH_OS_MAP_REGION
Function: In addition to the EMS page frame, some programs
can use additional addresses to access
expanded memory. This setting gives advanced
users the capability to adjust the size of the
additional EMS region.
See also "EMS_FRAME_LOCATION".
Advantages:An advanced user can use the MEM_EXCLUDE_REGIONS
and MEM_INCLUDE_REGIONS settings to specify the
addresses used by devices that do not have virtual
device drivers, and can then set the size of the
EMS_HIGH_OS_MAP_REGION appropriately for their
program. This helps avoiding conflicts with
addresses used by devices and programs.
Default: The value set is the size of the region in
kilobytes. The default is 32KB.
Settable: At VDM creation only.
Examples: None.
EMS_LOW_OS_MAP_REGION
Function: Some programs can use remappable conventional
memory. Others do not use this feature. This
setting allows advanced users to set the size
of the remappable conventional memory
available in a VDM.
Default: The value set is the size of the region in
kilobytes. The default is 384KB.
Settable: At VDM creation only.
Examples: None.
EMS_MEMORY_LIMIT
Function: This setting controls the amount of EMS memory
available to a VDM.
Advantages:You can set this to a higher value for
running programs that require a large amount of
EMS memory. Other programs do not use EMS at
all. The size can be set to 0 in such cases,
to disable EMS support for that VDM. Programs
generally state if they use EMS on the box or
in their documentation.
Default: The value set is the size of the region in
kilobytes. The default size is 2MB.
Settable: At VDM creation time only.
Examples: If a spreadsheet runs out of memory,
the amount of EMS memory can be
increased and the VDM restarted.
HW_NOSOUND
Function: Enables or disables sound started by a DOS
program.
Advantage: Any sound from a program is heard unless sounds
is disabled. An "x" in the check box indicates
that the sound should be heard.
Drawbacks: No error sound is heard if HW_NOSOUND is
turned on.
Default: OFF.
Settable: At any time, including while a program is running
in a VDM.
Examples: Output from a music program may
be disabled when you want to
hear another music program, or
switch to another session.
HW_ROM_TO_RAM
Function: Enabling HW_ROM_TO_RAM causes the operating
system to copy read-only memory (ROM) and run
the copy in 32-bit random access memory
(RAM). With this setting enabled, BIOS
operations run faster and system utilities may
patch BIOS.
Default: OFF.
Settable: At VDM creation only.
Examples: This setting is useful if debugging
the kernel. The change allows
normal breakpoints to be set in ROM and
allow stepping over calls and loops.
Warning: If an application writes to a memory address
used by the ROM while this setting is enabled,
it may cause unpredictable results for that
application and for every application run
thereafter in the VDM.
HW_TIMER
Function: When enabled, allows an application to have
direct access to the 8253 timer ports and
prevents the operating system from trapping,
or intercepting, the timer request and emulating a
timer.
Advantages:Certain timing-critical applications do not
run (or run much slower) if accesses to
timer ports are trapped and virtualized. In
addition, the values they read do not
accurately reflect the amount of time passed
because they do not take trapping overhead into
account. Enabling this setting allows certain
timing-dependent code to run more effectively.
Drawbacks: Applications that change the divisor before this
setting is enabled and then read the timer
ports after the setting has been enabled may not
function properly. If the setting is enabled
first, the VDM does not detect changes to the
divisor correctly, and the simulated interrupt
frequency will be incorrect. Also, multiple
applications using this setting may interfere
with one another.
Default: Off. Most applications operate normally with
timer virtualization.
Settable: At any time. It is useful to change this setting
dynamically and watch for changes in application
performance.
Examples: The ROMs on some machines implement
very brief delays by polling the timer
ports. These delays become unacceptably
long unless direct timer port access is
allowed.
IDLE_SECONDS
Function: When programs appear to be doing nothing but
waiting for input, the operating system gives
them less time to run. This is done to give
preference to programs that are doing useful work.
Some programs periodically appear to be waiting
for input, but then change their behavior and
continue after a time. This setting disables the
"IDLE_SENSITIVITY" function for a period of time
after useful work has been detected.
Also see "IDLE_SENSITIVITY" below for more
details on idle detection.
Advantages:If a program appears to run slowly when there is
an option for the user to provide input,
this value should be increased.
Drawbacks: Setting the value too high gives the DOS program
more resources than it needs.
Default: This value is in seconds. The default is no idle
time allowed.
Settable: The setting can be changed while the program is
running to tune it to the proper value.
Examples: A game may pause, for instance, to wait for the
user to make a choice, but then continues if the
user does not react.
- When DOS 5 is run in a virtual machine
boot session, the DOS shell may fail to
complete displaying the directory of the
C: drive if IDLE_SENSITIVITY is set too
low. IDLE_SECONDS should then be raised.
IDLE_SENSITIVITY
Function: The idle sensitivity level sets a threshold for
judging when applications are considered
idle. The value is the percentage of the maximum
possible polling rate the application can perform.
If an application polls at a rate higher than
this value, it is considered "idle."
DOS programs often "poll" for input when they
are waiting for a user response. For instance, a
program may wait for a response by repeatedly
checking to see if the user has hit a key. In a
multitasking environment such as OS/2 Version 2.X,
this wastes time when other programs could
be running instead. The operating system
detects idle programs by looking for a high
rate of polling for input. When programs are
judged to be waiting for input, they are given
less time to run.
For example, if idle sensitivity is set to 75%,
then an application repeatedly checking to see if
input is available would have to do this checking
at more than 75% of the maximum possible rate
before it would be judged idle. Idle detection is
a "best guess" of what the program is doing. It
could be that the program is polling at a very
high rate, but is still doing useful work in
between checking. It may be that the application
checks at a fairly slow rate but still is doing
nothing but waiting. The idle sensitivity
threshold allows adjustment of the threshold for a
particular application. Also see "IDLE_SECONDS"
in topic.
Advantages: If an application receives input while running
and seems to run slower than expected, the idle
sensitivity should be set to a higher value.
This lets the application poll at a higher rate
without being judged idle. Setting the level to
100 turns idle detection off altogether. The
application will be allowed to poll for input as
often as it likes. If an application is waiting
for input and other applications do not appear
to be running, the idle sensitivity should be
adjusted downward. This lowers the threshold for
judging the application idle.
Default: The default is 75%.
Settable: The setting can be changed while the program is
running to tune it to the proper value.
Examples: Overall system performance can usually be
improved when there are multiple DOS
applications running if IDLE_SENSITIVITY is
turned down.
Also see "DOS_BACKGROUND_EXECUTION"
*INT_DURING_IO
Function: When set on, this creates a second thread for the
application to use for interrupt handling when
the primary thread is busy with I/O operations.
Advantage: Very useful in multimedia applications, MSCDEX
applications, and many games.
Disadvantages: This does create extra overhead on the system
for processing and memory requirements and can
cause degradation of performance for other
applications.
Default: Off.
Settable: At VDM creation only.
Example: Unless your application is interrupt sensitive,
leave this setting OFF.
KBD_ALTHOME_BYPASS
Function: When enabled, prevents the Alt+Home key
sequence from switching the VDM between full
screen and windowed mode.
Advantages:Enabling this setting allows normal behavior for
applications which themselves make use of the
Alt+Home key sequence.
Drawbacks: When enabled, you must use the Ctrl+Esc
sequence to switch to Presentation Manager from a
full screen VDM, then use the context menu of
the class to switch the VDM to windowed mode.
Default: Off (Alt+Home causes a switch between
full screen and windowed mode).
Settable: At any time.
KBD_BUFFER_EXTEND
Function: Increases a VDM's keyboard type-ahead buffer size.
Advantages:Provides greater keystroke buffering,
consistent with the level available in VIO
windows. Note that Ctrl+Break flushes the
entire buffer, just as it does with the standard
buffer.
Drawbacks: Applications that bypass the ROM BIOS input
buffer and/or INT 16h may not benefit from
this feature. There is also a small amount of
additional memory overhead for every VDM.
Default: On. Most applications benefit, and those
that do not should not be adversely affected.
Settable: At any time. This facilitates easy
experimentation in the rare event
that a problem does arise.
KBD_CTRL_BYPASS
Function: When enabled, inhibits one or more control
key sequences, allowing an application in the VDM
to use these sequences for its own purposes.
Advantages:Enabling this setting allows normal behavior for
applications which make use of control key
sequences normally used by OS/2
Drawbacks: Enabling this setting may prevent certain
operations from being performed with OS/2
Version 2.X and the Workplace Shell.
Default: NONE (All control key sequences behave in the
normal manner).
Settable: At any time.
KBD_RATE_LOCK
Function: Prevents a DOS application in a VDM from changing
the system keyboard repeat rate.
Advantages:Insulates machine from applications that modify
the repeat rate in an uncontrolled or undesirable
way.
Drawbacks: Prevents the application's repeat rate from
taking effect even when the application is the
focus session.
Default: Off. Most applications do not modify the repeat
rate.
Settable: At any time.
MEM_EXCLUDE_REGIONS
Function: Specifies address ranges that should be
protected from use by EMS/XMS and direct access
by applications. This setting is for
experienced users that understand the hardware.
Advantages:This setting restricts the use of EMS/XMS on
certain ranges in the region between RMSIZE and
1MB. It also protects these ranges from being
touched by user applications by portraying
ROM there.
Drawbacks: Some hardware adapters stop functioning if
their addresses are touched in random fashion.
If these ranges are defined excessively, they
adversely impact the function and performance of
EMS and XMS services.
Default: By default, this setting is void. Each address
is specified in hex and if there is no range
specified, the length taken is a page (4KB).
Settable: At VDM creation only.
MEM_INCLUDE_REGIONS
Function: Specify regions that should be made available
to EMS/XMS. This setting specifies address ranges
between RMSIZE and 1MB for use by EMS and XMS.
Advantages:If there is a hardware adapter in this range
that the user knows is not going to be used by a
particular VDM session, then the address
range used by this adapter should be made
available to EMS and XMS. This improves the
performance of EMS and XMS services. Only
advanced users who know the addresses used by a
card should use this setting.
Default: By default, this setting is void.
Settable: At VDM creation only.
MOUSE_EXCLUSIVE_ACCESS
Function: Allows VDMs to run applications that maintain
their own mouse pointers. Some DOS applications
manage their own mouse positions and movements; in
many cases, the application's values for mouse
sensitivity and/or double speed threshold are
different from those of Presentation Manager. As
a result, a Presentation Manager mouse pointer may
be outside the VDM window while the application
pointer is somewhere in the window not receiving
any mouse events. This means having two
asynchronous mouse pointers on the screen.
Advantages:You force the physical mouse driver to
send its events directly to the virtual mouse
driver without going through Presentation Manager.
Only one mouse pointer appears when the particular
VDM window has the focus.
Default: OFF.
Settable: At any time. However, this only marks the VDM
window and does not actually activate the setting.
To activate it, press a mouse button in the VDM
window. The Presentation Manager pointer
disappears, leaving only the application pointer.
To regain the Presentation Manager pointer, press
any of the hot-keys (Alt, Ctrl +Esc,Shift+Esc).
Examples: WordPerfect 5.1 has its own block-shaped mouse
pointer, that appears together with the
system mouse pointer when the window has the
focus. Turning MOUSE_EXCLUSIVE_ACCESS on
allows the user to remove the system mouse
pointer when in WordPerfect.
PRINT_TIMEOUT
Function: Use this setting to adjust the amount of time, in
seconds, that the OS/2 V2.X print subsystem waits
before forcing a print job to the printer. In DOS,
information sent by a program for printing goes
directly to a printer. However, the OS/2 V2.X
print subsystem assembles print information in a
spool file. After a specified period of time,
during which the spool file does not grow larger,
OS/2 V2.X print subsystem sends the information to
the printer as a single print job.
Advantage: There is no need to exit the DOS program before
the print job is released by the OS/2 V2.X print
subsystem. This is useful for applications
that do not explicitly close their print jobs.
Default: 15 seconds, configurable from 0 to 3600 seconds
(0 seconds is no timeout).
Settable: At any time.
Examples: A timeout of 1 or 2 seconds is fine for small
print jobs, like copying the contents of the
screen. However, when printing large files,
formatting documents, or running calculations,
the value must be set high enough to allow all
print results to reach the spooler before the
time limit expires. If not, results go in two
or more spool files instead of one, and the
resulting output may be unsatisfactory.
VIDEO_FASTPASTE
Function: Speeds up input from other sources than the
keyboard.
Advantages:Improves the speed of paste operations
from the clipboard to a DOS application.
Drawbacks: Does not work with all applications (in
particular, some applications that monitor
keyboard interrupts directly may experience
errors).
Default: Off.
Settable: At any time. This facilitates easy
experimentation.
Examples: Pasting into the DOS command prompt, or any
application using DOS Console I/O functions,
generally works. 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, that can overflow.
VIDEO_MODE_RESTRICTION
Function: Extends the 640KB DOS address space by limiting
video mode support.
Advantages: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.
Drawbacks: 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 be taken when using
this feature.
Default: NONE. The complete list of settings is:
- None
- CGA modes only (adds 96KB)
- MONO modes only (adds 64KB).
Settable: At VDM creation only.
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 you are
able to free memory from another session, you 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 lets you save memory
the next time the session is switched to
full-screen.
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
to 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
experience some drag in performance.
Settable: At any time. This lets you experiment
with different settings in the event of a
performance problem.
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 run
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 lets you experiment
in the event of a compatibility problem.
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)
that are not fully supported by the OS/2 video
driver or 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").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 can
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 lets you experiment
in the event of a compatibility problem.
Examples: Windows 2.x and 3.x understand this
notification and 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
results 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, that not all applications
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
not complete information about its state.
Default: Off.
Settable: At VDM creation only.
Examples: When running Windows 3.0 with the 8514/A
display driver, certain operations such as
painting dithered backgrounds run significantly
faster.
WIN_CLIBOARD
Function: When set on, the sessions to share clipboard
information among OS/2, DOS (window),
and Windows programs. While this setting is on
the clipboard is public. Windows programs can
share data with other DOS, Windows, and OS/2
programs, as long as you select public clipboard
on the Data exchange page from WIN-OS/2 setup
object, in the sytem folder. Otherwise, you can
share information only with other Windows programs
in that session. When that setting is set to off,
the clipboard is private and Windows programs
cannot share clipboard information with other DOS,
Windows, and OS/2 programs.
Default: On (Public).
Settable: At any time.
WIN_DDE
Function: When set on, this enables sharing of data
among other OS/2 and Windows programs. While
enabled the dynamic data exchange (DDE) is public.
Windows programs that support DDE automaticly
update identical data in other Windows and OS/2
programs.
If you select public DDE on the Data Exchange
page from the WIN-OS2 Setup object, in the system
setup folder. Otherwise, you can share information
only with other Windows programs. When this
setting is set to off, DDE private and Windows
programs cannot share DDE information with other
windows and OS/2 programs.
Note: If you are running multiple Windows programs
in a single WIN-OS/2 session and the program
supports the DDE feature, it is possible to
share DDE information between these programs
even when this setting is off (Private).
Default: On (Public).
Settable: At any time.
WIN_RUN_MODE
Function: This setting is only listed in the WIN-OS/2
setting window and does not apply to DOS window or
DOS full-screen sessions.
OS/2 can use two modes to run Windows programs:
- 3.1 Standard
- 3.1 Enhanced
Default: 3.1 Standard.
XMS_HANDLES
Function: Specifies the number of XMS extended memory block
(EMB) handles. A handle is used with each XMS
EMB. This number is required because XMS
pre-allocates all the handle space to be
compatible with XMS specifications. This setting
should be used only if an application uses a large
number of handles.
Advantages: This setting restricts the number of block
handles, thereby reducing memory consumption.
Drawbacks: Specifying a large number of handles increases
memory consumption and adversely impacts system
performance.
Default: The default value of this setting is 32.
Settable: At VDM creation only.
XMS_MEMORY_LIMIT
Function: Specifies the per VDM XMS memory limit. This
setting should be used under the same guidelines
as described above in "XMS_HANDLES". The global
limit is the overall maximum XMS memory
consumption, and the per-VDM limit is the maximum
allowed for each VDM. See also "Initialization"
for defining global and per-VDM limit in the
CONFIG.SYS.
Drawbacks: Specifying a large number may adversely
affect system performance.
Default: The default value is 2MB per-VDM.
Settable: At VDM creation only.
XMS_MINIMUM_HMA
Function: Specifies the minimum HMA memory request allowed.
This setting lets you fine tune the XMS.
HMA is slightly less than 64KB in size. Only one
request can be fulfilled from this area at a time.
Advantages: If a TSR takes a very small allocation, then it
wastes this area for other applications.
In such cases, a limit can be specified.
Default: The default value is zero, which means all the
requests are allowed.
Settable: At VDM creation only.
Examples: 2048; this sets a limit of 2KB.
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