With a typical installation of the CS WinOMS software, patient information, treatment records, billing, and A/R records are stored in the Data folder of the server computer:
C:\WinOMSCS\Data
If your system is configured to store images or other important files in a different location or on a different computer, make arrangements to back up those folders as well.
Since individual configurations can vary, verify the location of this folder and any other essential folders with the technician who installs and maintains your backup system.