ISO/IEC 9318-4:2002

This part of ISO/IEC 9318 describes the logical level (generic level) interface for tape drives and it provides a definition of the device-generic portion of a family of standards called the Intelligent Peripheral Interface (IPI).

The purpose of this standard is to facilitate the development and utilization of an intelligent interface which permits the interconnection of multiple peripheral types such as disk, tape and communications to a controller.

The intent of the IPI is to isolate the host (CPU), both hardware and software, from changes in peripherals by providing a "function-generic" command set to allow the connection of multiple types of peripherals (disks, printers, tapes, communications). To smooth the transition from the current methods to the generic approach, the IPI supports device-specific command sets to aid in bridging the gap between the two approaches.

To accomplish this set of goals, the design of the IPI includes device-specific and devicegeneric command sets. The device-specific command set provides:

• device-oriented control;
• physical data addressing;
• timing critical operations;
• lower device cost.

The device-generic command set provides a higher level of functionality and portability. It includes:

• host/device independence;
• logical data addressing;
• timing independence;
• command queuing capability.

A system is not restricted to the use of one level of command set or the other. It is possible that both levels of command sets will be utilized with a given system's architecture to balance such parameters as system performance, cost and peripheral availability. It is also possible for the host to provide for the migration from device-specific to device-generic levels while still retaining the same physical interface.

The IPI standards family includes the definition of a high performance, general-purpose parallel peripheral interface. However, the device-generic command set may also be transported over other non-IPI physical interfaces. ANSI X3.291:1997 contains "mappings" to the High-Performance Parallel Interface (HIPPI) and Fibre Channel (FC) as well as to the IPI Enhanced Physical Interface. The "mappings" are not contained in this document.