required files(drivers directory in UltraISO installation):
isocmd.exe
ISODrive.sys
ISODrv64.sys

related reg key:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ISODrive

useful parameters:
isocmd -number 3
set how many devices to be emulated
HKLM\SYSTEM\CurrentControlSet\Services\ISODrive\Parameters\NumberOfDevices
DWORD 0x0000003
isocmd -install
install the drive and service named ‘ISODrive’
D:>sc start ISODrive
SERVICE_NAME: ISODrive
TYPE : 2 FILE_SYSTEM_DRIVER
STATE : 4 RUNNING
(STOPPABLE, NOT_PAUSABLE, IGNORES_SHUTDOWN)
WIN32_EXIT_CODE : 0 (0x0)
SERVICE_EXIT_CODE : 0 (0x0)
CHECKPOINT : 0x0
WAIT_HINT : 0x0
PID : 0
FLAGS :
D:>sc getdisplayname ISODrive
[SC] GetServiceDisplayName SUCCESS
Name = ISO DVD/CD-ROM Device Driver
isocmd -print
output version information and emulated devices
D:>isocmd -print
ISODrive V3.11.409
Number of Devices=1, DriveLetters=[E]
isocmd -mount X: xxx.iso
isocmd -eject X:
isocmd -remove
remove the service named ‘ISODrive’, remove drive

Documented parameters:
D:>isocmd
Usage: isocmd <-command>
-mount drive: file_spec (mount file_spec to drive:
password is optional for ISZ images)
-eject drive: (unmount drive:)
-number (set number of devices)
-change device_no new_drive_letter: (change drive letter)

Remarks
If you want to change the number of emulated devices, you have to reinstall service.
i.e.
isocmd -remove
isocmd -number 32
isocmd -install