Device Operating Modes

Most devices attached to z/OS operate in full-function mode; that is, all features on the device are compatible with and usable on the operating system. Some of these features include:

DASD devices:
- Dynamic path reconnection
- Extended count-key-data operation
- Caching and cache related facilities
Tape devices:
- Cartridge stack loading
- Data compaction

Some devices also operate in compatibility mode, which lets you simulate the function of another device or model. Compatibility mode causes the device to function like a different device of the same type, ignoring some or all of the additional features that the device might have. This allows you to migrate between devices with minimal impact on programs that have device dependencies.