ITs not really a function in either window(MIX or EDIT) but its a checkbox to tell PT how to address hard drives(it might be found on the Workspace page, but I'm not sure as I have not seen or used the workspace in a decade). "Record" means that you can record to that drive. "Transfer" means that the drive can only be used to transfer data to another session or system, but cannot be recorded to. Search the help files(aka the manual) for more details
