Using SYSTEM.INI's COMMDRV30 Switch

• Microsoft Windows operating system versions 3.1, 3.11

SUMMARY

This new switch for the Microsoft Windows operating system version 3.1 indicates to the Virtual COM Device Driver (VCD) that it needs to configure itself to handle hardware interrupts for COMM.DRV in the same manner as in Windows 3.0. This switch is needed only if you are using enhanced mode and have a third-party COM driver, but don't have a replacement VCD.

MORE INFORMATION

In Windows 3.0's enhanced mode, the VCD is responsible for handling the COM port hardware interrupts for COMM.DRV, and thus Windows applications. In Windows 3.1, COMM.DRV handles its interrupts directly; therefore, the VCD can be smaller because it doesn't have to duplicate the interrupt handling code.

A problem arises when a third-party COM driver is being used. A number of third-party COM drivers are replacements for Microsoft's COMM.DRV, but they may not have replaced Microsoft's VCD. For these third-party COM drivers, it is still necessary for Microsoft's VCD to handle the interrupts. To provide this compatibility and still shrink the VCD code for a default installation, Microsoft made the VCD configurable.

If "COMMDRV30=TRUE" is added to the [386Enh] section of the SYSTEM.INI file, then the VCD will allocate memory and include the code to handle interrupts for the Windows 3.0-compatible COM driver.

This switch applies only to enhanced mode Windows. It does not affect MS-DOS applications or the performance of the Windows 3.1 COMM.DRV.