DOS and WIN-OS/2 Settings

Every object (including program objects) has settings. A user can adjust DOS and WIN-OS/2 settings to improve performance. Settings are properties or characteristics that tell the operating system how the object is different from other objects. Each object has a notebook or pop-up menu choice that allows a user to customize its settings.

For example, a user can customize the settings for a program object to tell the operating system how the application should start each time the program object is opened. Or a user might open the Mouse object to customize the mouse for left hand use.

DOS settings provide the ability to selectively configure and customize a DOS session to meet the requirements of a particular application. Some DOS applications require certain features; others operate better without them. Thus, an individual DOS session can be set up to provide the optimum environment for the application that will run within it.

DOS settings can be changed in either of two ways:

• Settings that can be set only at the time the session is created must be changed prior to starting the DOS session.

• Settings that can be set at any time can be set prior to starting the DOS session, or while an application is running in the session.

The OS/2 2.0 Master Help Index has detailed information about settings.

The following is a list of some settings that control the functioning of screen I/O operations within a DOS session:

VIDEO_WINDOW_REFRESH

Adjusts the time that elapses before a window is redrawn. The values range from 0.1 second to 60.0 seconds (1 minute).

• Increasing the value increases the delay between screen redraws if an application is run (such as a graphics application) that writes frequently to video memory. Increasing the delay between each writing to video memory frees the processor for other application tasks, but increases the delay between screen redraws.

• The default value is 0.1, which represents the interval between window updates.

DOS_BACKGROUND_EXECUTION

Allows DOS applications to run in the background.

• When the setting is set to ON a DOS application runs when it is in the background.

• When the setting is set to OFF a DOS application is suspended when it is in the background. When the DOS application is suspended, it no longer receives interrupts.

• The default is ON.

VIDEO_8514A_XGA_IOTRAP

This setting is used to directly access the Model 8514/A or XGA video.

• Setting this to OFF might make an application run faster. It releases the 1MB of allocated memory where video information is saved in a DOS session.

• Set this to OFF for all WIN-OS/2 sessions that run in 8514 or XGA video modes.

• The default is ON to ensure that the screen image is restored when the screen is switched.

VIDEO_SWITCH_NOTIFICATION

Notifies a DOS application about a switch between background and foreground.

• If this setting is ON, programs that monitor screen switching will save or redraw the screen when the screen is switched. For WIN-OS/2 sessions, set this to ON.

• The default is OFF, because most standard video modes do not use screen switch notification.

The following is a list of some settings that affect the behavior of the OS/2 2.0 DOS emulation environment within a DOS session:

COM_HOLD

Gives exclusive use of a particular communications port for a DOS session (for example, COM1). ON prevents other sessions from using the same COM port until the DOS session ends.

• Select ON if there is difficulty maintaining communication between a DOS application and a bulletin board.

• The default is OFF.

HW_TIMER

The timer hardware access setting is used to give an application direct access to Model 8253 timer ports. Set this to ON to prevent the operating system from trapping, or intercepting, the timer request and emulating a timer. Also set it to ON for timing-critical applications.

The default is OFF, which disables direct access to timer ports.

The following is a list of some settings that affect the hardware environment provided by a DOS session:

DOS_BREAK

The break setting is used when a user wants the OS/2 operating system to check for the Ctrl+Break or Ctrl+C key combinations while an application is running.

• Applications run more slowly when this setting is set to ON.

• The default is OFF.

HW_ROM_TO_RAM

Copies the Basic Input/Output System (BIOS) from ROM to RAM.

• When this setting is set to ON, applications might run faster.

• The default is OFF.

KBD_ALTHOME_BYPASS

The Alt+Home bypass setting reserves a key combination for the DOS session. Normally, pressing Alt+Home switches between a window session and a full-screen session.

• ON enables the application in a session to use this key combination for a different purpose. For example, select ON to reserve Alt+Home for a Windows application in a WIN-OS/2 session, particularly a WIN-OS/2 full-screen session.

• The default is OFF.

KBD_CTRL_BYPASS

The Control key bypass setting enables a user to use either Alt+Esc or Ctrl+Esc in a DOS session. Normally, Alt+Esc switches between sessions; Ctrl+Esc displays the Window List.

• The default is NONE.

• Enables switching between tasks in WIN-OS/2 sessions.

IDLE_SECONDS

Specifies the length of time the operating system waits before applying idle detection in a DOS session. The field for this setting shows the amount of idle time allowed in seconds. Values range from 0 to 60.

• Allows an idle period for an application, such as a game, that waits a brief time after prompting for input, but continues activity if there is no response. If an application appears to run slowly when waiting for input, increase the value in this field.

• The default value is 0.

IDLE_SENSITIVITY

Specifies a threshold for judging when an application is only waiting for input. The value in this field is a percentage of the maximum frequency with which an application repeatedly checks, or polls for input.

• Increase the percentage if the application can receive input while running and seems to run more slowly than expected. Selecting 100 in this field turns idle detection off, and the application can poll as often as necessary without operating system intervention.

• The default value is 75.

VIDEO_FASTPASTE

The fast paste setting is used to increase the speed of character Cut and Paste transfers between the clipboard and a DOS session.

• Set this to ON to increase the character speed of Cut and Paste transfers.

• The default is OFF.

VIDEO_RETRACE_EMULATION

Controls the frequency of video retrace. When this setting is OFF, retrace occurs only at the interval specific to the video mode of the running DOS application.

• A few DOS applications run more slowly with this setting set to ON.

• Changing this setting to OFF increases performance, but screen switching is not as reliable.

• The default is ON.

VIDEO_ROM_EMULATION

Controls the emulation of WriteChar, WriteTTY, and full-screen scroll video functions.

• Select OFF if video read-only memory (ROM) provides enhancements to these video functions.

• The default is ON, because the emulated functions enhance performance over most manufacturers' ROM versions of the same functions.

PRINT_TIMEOUT

Specifies the number of seconds that elapse before information is sent from a DOS application to a print spool file. The values range from 0 to 3600 seconds.

• Increase the value if the DOS session print jobs are incorrectly divided into more than one print file. This might occur for jobs that print large files, format documents, or run calculations.

• The default value is 15.

The following is a list of some settings that affect the behavior of the EMS and XMS memory extenders when used in a DOS session:

EMS_MEMORY_LIMIT

Defines the amount of EMS available to the DOS session. This setting is expressed in KB units, ranging from 0 to 32768.

• The value should be 0 if a DOS application does not need EMS. This might improve performance.

• This setting enables a user to limit the amount of EMS that an application reserves, which prevents an application from allocating more memory than necessary. A limit that is too high can slow performance.

• The default value is 2MB.

XMS_MEMORY_LIMIT

Specifies the amount of memory that a DOS session can allocate to XMS. This setting is expressed in KB units, ranging from 0 to 16384.

• Specifying a large number for either the global or the per session extended-memory limit can slow performance.

• The default value is 2MB.

DPMI_MEMORY_LIMIT

Defines the amount of DPMI available to a DOS session. This setting enables a user to specify the amount of DPMI memory needed for DOS applications on a per session basis. The field for this setting contains values expressed in 1MB intervals ranging from 0 to 512.

• The value should be 0 if a DOS application does not need DPMI.

• Increase this setting to 6MB for WIN-OS/2 sessions that run more than one application.

• The default value is 2MB.

DPMI_NETWORK_BUFF_SIZE

Controls the size in KB, of the network translation buffer for DPMI applications in a session. The range is from 1 to 64KB.

• This setting allows a user to set the size of the translation buffer for DPMI applications, for example, Windows applications that transfer data over a network.

• If a network-specific Windows application does not run correctly under OS/2 2.0, increase this setting, then restart the session.

• The default value is 8KB.

MEM_INCLUDE_REGIONS

Fills any areas between memory addresses of 640KB and 1MB that are designated for EMS, XMS, or a copy of a ROM application.

• Including regions can improve the performance of applications that use EMS or XMS memory.

• By default, this field is empty.