Hardware Environment

The following settings affect the virtual hardware environment provided by the virtual DOS machine.

HW_NOSOUND

Function:

Enables or disables sound started by a DOS program.

Any sound from a program is heard unless sound is disabled. An "x" in the check box indicates that the sound is to be heard.

No error sound will be heard if HW_NOSOUND is turned on.

OFF.

At any time, including while a program is running in a VDM.

Output from a music program may be disabled when the user wishes to hear another music program, or switch to another process to do something else.

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.

OFF.

At VDM creation only.

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.

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.

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.

Off. Most applications will operate normally with timer virtualization.

At any time. It is useful to alter this setting dynamically and watch for changes in application performance.

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.