International Business Machines Corporation

Charles R Kirkpatrick

Harry O Hempy

Scott Milton Fry

Bruce E Kittinger

Francis L Robinson

William C Dodt

Ted A Rehage

Wayne J Bauer

William K Taylor

Data transfers between respective buffer segments and data source-sinks, such as peripheral data storage devices, are scheduled as a series of transfers based upon most recent, next most recent, to the least recent usage of the buffer segments by a utilization device. A list of segments ordered by such usage is dynamically maintained. Replacement of segment allocations among devices proceeds from the least recently used, next least recently used, etc. to the most recently used segments. Therefore a single list controls replacement and read ahead (prefetch) of data from devices to the buffer and transfer of data from the buffer to the devices, all based on utilization of the buffer by the utilization device.

Scheduling device operations in a buffered peripheral subsystem

Data transfers between a host processor and a peripheral data recorder in a peripheral data storage system, such as tape recorder peripheral data storage system, are via a random-access buffer store in the peripheral data storage system and interposed between the peripheral data recorder and the host processor. A command queue storage in the peripheral data storage system stores commands received from the host processor for the peripheral data recorder. Additionally, apparatus in the peripheral data storage system form commands for transferring data between the peripheral data recorder and the buffer store without intervention of the host processor; both read transfers (data transfer from the peripheral data recorder to the host processor) and write transfers (data transfer from the host processor to the peripheral data recorder) are enabled via the formed commands.

Queuing commands in a peripheral data storage system

In a buffered data storage subsystem, data is promoted to the buffer in anticipation of a connected host using the promoted data in the near future. In a tape recorder data storage apparatus the actual position of the tape reflects the last promoted data; such actual tape position is 'inconsistent' with host operations. If the sequence of host operations continues, such inconsistency actually enhances total operations. When the subsystem detects a change or possible change in future host operations (rewind command, change in tape motion direction, etc.), detect end of file (tape mark) or a change in subsystem operations (load balance affecting drive or deallocation of buffer from drive) the data promoted to the buffer and not read by the host is erased from the buffer. The tape is moved such that upon a forward motion the tape drive would next read data on tape corresponding to the data block erased from the buffer.

Controlling buffered peripheral subsystems

A peripheral system has one or more buffered control units connected to a plurality of peripheral devices. Operation times of the devices are marked by the buffer and controls which overlap device operations, queue device operations in a priority set of queues, and prioritize peripheral system operations. Plural specialized interconnections between each control unit and the devices include a preparatory connection for transfer of preparatory commands to devices, a tag or control connection for device selection, deselection and control and a data-command connection for signal transfers between a selecting control unit and a selected peripheral device.

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Charles R Kirkpatrick