Function            isDriverSys - is DRIVER.SYS installed

  Syntax              unsigned char isDriverSys(void);

  Prototype in        doshk.h

  Remarks             checks if DRIVER.SYS is installed.

  Return value        returns one of the following values:

                           0x00 - not installed, OK to install
                           0x01 - not installed, not OK to install
                           0xFF - installed

  Example             #include <doshk.h>

                      main()
                      {
                           printf("DRIVER.SYS is ");
                           if (isDriverSys() != 0xFF)
                                printf("not ");
                           printf("installed\n");
                      }