If having opened access to the Upper Memory Block (UMB), then one can load CDROM-drivers and other Terminate and Stay Resident (TSR) programs like DOSKEY.EXE into the Upper Memory Block (UMB) to increase the available conventional memory.

Edit AUTOEXEC.BAT and use LH/LOADHIGH:

LOADHIGH DOSKEY.EXE

Edit CONFIG.SYS and use DEVICEHIGH:

DEVICEHIGH=C:\CDROM\DRIVER.SYS

Note that if there is not enough free memory for the device to load in the UMB, then the device is loaded in the conventional memory. Therefore it might be a good idea to Check how much memory each TSR program uses and then order the loading of the TSR programs so the UMB is packed completely.

More Info MS KB151718
More Info MS KB72183
More Info MS KB96028
More Info MS KB95555
More Info MS KB76820