consists of two 32-bit tokens (composed of the driver's manufacturer ID combined with a 16-bit constant). One token indicates the underlying storage format and refers to a single well-defined data driver. The other token defines the way data are stored in that underlying storage format. From an application's point of view, each data format token can only be used with one particular storage type token. Passing both allows things like the pager driver, described earlier, to be more flexible in how a message i