The Read Naturally SE v2 server software runs as a service under Windows (see the list of supported operating systems). Since the SE server software is installed into the operating system, you must install it on the same physical hard drive where Windows is installed.
In Windows, a drive letter can represent either a separate physical drive or a logical partition of a physical drive. You can install the SE server software on any logical partition that resides on the same physical drive where Windows is installed. However, you cannot install the SE server software to a drive letter that represents a separate physical drive.
Please let us know what questions you have so we can assist. For Technical Support, please call us or submit a software support request.