The latest version is IBM Cognos 8.4 which has a single installation platform for all Cognos products. Using this version requires web services for authentication and a relational content store to hold user information.
For customers with Analyst / Manager only applications IBM Cognos 8.1 is supported until March 2011 and this version does not require web services for authentication or a content store and represents a simpler upgrade option.
At version 7.1 the Excel add-in was significantly enhanced. To continue to use Excel reports from previous versions it is necessary to first upgrade to Cognos 7.1, open and refresh all Excel reports, then upgrade to the most recent version
Cognos Planning 7.3 onwards requires the use of a separate authentication component called Access Manager which needs to run as a server process to log people on instead of the mechanism used in previous versions.
From version 8.2 onwards authentication is performed through external company systems such as Active Directory though Access Manager can be retained if required.