Roland UM-4 Owner's Manual page 37

Windows Users
If you use multiple UM-4 units, device numbers will be added to the beginning of the device
name to indicate the order (connection order) in which the computer recognized each UM-4
unit.
fig.04-03UM4.e.eps_50
OMS Users on Macintosh
If you connect multiple UM-4 units and make OMS settings (P.24), multiple "Roland UM-4"
items will appear in step 5 (P.26), as shown in the illustration. Simply click [OK], and follow
the procedure to check all of the ports.
fig.04FUKUSU_Mac1.e
Appendices
37