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1994-12-02
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DOS Settings, Description of Each 7/18/94
FILE: OSDASET.FAX - 6/02/94
TITLE: 940602 DESCRIPTION OF DOS SETTINGS FOR
AN OS/2 DESKTOP ICON
DESCRIPTION:
STANDARD DOS SETTINGS
---------------------
This document describes the ability of 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 will allow 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 which use COM
ports and which require multiple programs to
access the COM port (for example, this setting
prevents the COM port from being released when
the first program terminates).
Drawbacks: If not required by the application running in a
VDM, this setting may prevent other
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 terminates.
COM_RECEIVE_BUFFER_FLUSH
Function: Will allow 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 that, 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 that, 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, this will allow 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
will 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
that 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" in and
"IDLE_SECONDS"
Drawbacks: Communications programs will fail if background
execution is turned off, as will 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; the user may easily
terminate a VDM by closing it from the Window
List.
Default: Off (Ctrl+Break is disabled).
Settable: At VDM creation only.
Examples: If the user wishes to have the option to
interrupt a DOS batch file running in a
virtual DOS machine, this setting should be
turned on.
DOS_DEVICE
Function: This setting can be used 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
displayed which contains information about each
DOS device driver specified in 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
The user may:
- 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 that is 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) which may be opened by
applications running in the VDM. Note that this
setting affects only those modules which 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 which 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
FCBs that will be 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
which may be opened in a VDM.
Advantages: Setting this value higher than the default
may improve performance for applications
which 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 which require access to DOS
internal control structures require DOS to be
loaded into low memory, and therefore 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 which is 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 a user has
a different command processor, it should be
specified here.
Advantages: The user may 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, which 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 which make use of UMBs need
to access and manage the UMBs directly; such
applications will 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, in order to support
applications which check for a DOS version
number.
Advantages: Allows some programs that will 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+ will run 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 whether 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 which 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 which programs can access expanded
memory. (This allows programs to use more than
640KB of memory.)
Advantages: If a user has problems when 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, the user should
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. The user can choose where to
place the frame from a list of choices or can
choose to have no EMS frame for programs which
do not require a frame. The user can also
reduce the DOS Memory Size setting and place
the frame below 640KB.
Drawbacks: The best solution, when problems due to
hardware conflicts occur, 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 will lead to correct
choices of LIM EMS addresses. Most users will
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: The user 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 whether they use EMS on the box or
in their manuals.
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 is to be heard.
Drawbacks: No error sound will be 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 the user wishes 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 would allow 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 will not
run (or will 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 will 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 will operate
normally with timer virtualization.
Settable: At any time. It is useful to alter 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 will be 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, the user 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 will cause 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 will flush the
entire buffer, just as it does with the standard
buffer.
Drawbacks: Applications which 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 will benefit, and those that
do not should not be adversely affected.
Settable: At any time. This facilitates easy
experimentation by the user 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, and those that do are generally in
accordance with the user's wishes.
Settable: At any time.
MEM_EXCLUDE_REGIONS
Function: This setting is used to specify address ranges
which should be protected from use by EMS/XMS
and direct access by applications. This
setting is intended for experienced users who
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
will 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 which should be made available
to EMS/XMS. This setting is used to specify some
address ranges between RMSIZE and 1MB for use
by EMS and XMS.
Advantages: If there is a hardware adapter in this range
which 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 will improve the
performance of EMS and XMS services. Only
advanced users who now 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: This setting allows VDMs to run applications
which 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: The user forces 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. In order to
activate it, the user must press a mouse button
within the VDM window. The Presentation
Manager pointer disappears, leaving only the
application pointer. In order to regain the
Presentation Manager pointer, the user must
press any of the hot-keys (Alt, Ctrl+Esc,
Shift+Esc).
Examples: WordPerfect 5.1 has its own block-shaped mouse
pointer, which will appear 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
which 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 sufficient for
small print jobs, such as 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 which monitor
keyboard interrupts directly may experience
errors).
Default: Off.
Settable: At any time. This facilitates easy
experimentation by the user.
Examples: 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.
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 therefore
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 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.
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.
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.
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" 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 innecessary 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 u
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.
WIN_CLIBOARD
Function: When set on, this will allow the session 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 privateand
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 will enable 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 will
increase memory consumption and adversely impact
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 allows the user to 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
will waste this area for other applications.
In such cases a limit can be specified.
Default: The default value is zero, which means all the
requests will be allowed.
Settable: At VDM creation only.
Examples: 2048; this sets a limit of 2KB.
Report by: OS/2 Dosap Analyst Team - 06/94
IBM - Boca Raton, Florida
12/31/99
