Using the dos=umb command
To use the devicehigh command, you must also include the dos=umb command in your CONFIG.NT or equivalent startup file. If you do not specify
this command, all device drivers are loaded into conventional memory, as if you
had used the device command. For more information about the umb switch, see the dos command.
Before you can load a device driver into the upper memory area, you must use
the device command to install the HIMEM.SYS device driver. This command must appear
before any devicehigh command in your CONFIG.NT or equivalent startup file.
Specifying a size limit
If the device driver you specify on the devicehigh command line attempts to allocate more buffer space than is available in a
block of the upper memory area, your system may lock up. You can try using the hexsize parameter to avoid this problem. In hexsize, indicate, in hexadecimal format, the amount of memory the device driver
needs. To find this value for a particular device driver, load the driver into
conventional memory and use the mem /debug command. This method is usually, but not always, effective.
If no upper memory area is available
If there is not enough upper memory area available to load the device driver
you specified with the devicehigh command, the MS-DOS subsystem will load it into conventional memory (as if
you had used the device command).
More Information About Devicehigh