International Business Machines Corporation

John L Burk

Michael Howard Hartung

John Ted Rodell

Carl Edward Clark

Brian B Moore

David E Stucki

Kenneth R Lynch

Carl Zeitler, Jr

Roger L Cormier

Howard Loomis Page

Justin R Butwell

David H Wansor

Ray A Larner

Donald J Lucas

The embodiment provides selective supervisory disablement of fetch protection for a special storage subarea (such as for the first half of the first 4KB block) while fetch protection is enabled for an area containing the subarea by a single storage protect key. That is, the fetch protect for the subarea (normally provided in the fetch protect for the entire area) by the area's protect key is overriden by the selective subarea disablement control, so that accesses to the subarea are not fetch protected by the storage key. The override protection control is secured by its enablement via a field position in a control register only accessible to supervisory programming. Thus, while fetch protection is set on for a predefined 4KB block, the fetch protect override controls can disable the fetch protection for a portion of the block's real addresses (e.g. addresses 0-2047).

Storage fetch protect override controls

Secondary storage subsystems exchange messages and data with host data processing systems and also forward messages between host systems. Host systems thereby communicate with each other in addition to having access to data in subsystem storage. Access to subsystem storage is initiated by a 'request' sent from a host to the subsystem. Each request is a message containing an array of one or more commands, each command specifying a transfer of data or a control function to be performed by the subsystem. A subsystem may process more than one request at a time. It also may process the commands in a request in an arbitrary sequence suited to the availability of subsystem resources and data links to host systems. After all commands in a request have been processed the subsystem transmits an associated 'completion' message to the host system which originated the request. The completion message indicates the status of completion or abnormal termination of each command in the associated request. An 'adapter' processor associated with each host and subsystem operates on an asynchronous basis to transfer messages and data relative to the associated host or subsystem. One or more processing 'engines' in each adapter communicates with one or more CPU's in the associated host or subsystem through an associated 'adapter store'. A portion of each adapter store is used as a buffer pool for constructing 'subchannel control spaces' to control transers of messages and data. Elements of each subchannel control space are returned to free status as soon as they are not needed for sustaining associated transfers.

Block transfers of information in data processing networks

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Poughkeepsie, NY, United States of America

John L Burk