OsiriX  have both options means -  Storage and viewer basically called Osirix was PACS but **stand alone**.  Every PACS has its own viewer now a days either server client basis or web viewer. Dicom work station was different and PACS viewer was different.

RIS was Radiology information System which contains Process of Radiology dept. Scan orders > scheduling > Generating Modality work list >  scan reports > Modality reports > MIS reports > Billing (Optional) > Radiology reporting > Reports dispatch > Sending reports to PACS etc.   IT will communicate with PACS thorugh HL7.  PACS and RIS should be two different servers but some are available both in same then it wont suitable for bigger workflows.