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Logical Data Interface

IP.com Disclosure Number: IPCOM000079852D
Original Publication Date: 1973-Sep-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 4 page(s) / 19K

Publishing Venue

IBM

Related People

Casey, DP: AUTHOR

Abstract

The IBM 3830-2 is a programmable storage control unit. It maintains tables that reflect the contents and utilization of direct access storage device (DASD) volumes attached to it. It also controls the movement of data from an attached cartridge library to the DASD volumes. The 3830-2 is thus an instance of "outboard intelligence"; i.e., a programmable hardware component that is exterior to the CPU. Described below is a proposal for the use of such a hardware component (hereinafter called an "Outboard Data Manager - ODM") to provide a new, higher level I/O interface for system 370 CPUs.

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Logical Data Interface

The IBM 3830-2 is a programmable storage control unit. It maintains tables that reflect the contents and utilization of direct access storage device (DASD) volumes attached to it. It also controls the movement of data from an attached cartridge library to the DASD volumes. The 3830-2 is thus an instance of "outboard intelligence"; i.e., a programmable hardware component that is exterior to the CPU. Described below is a proposal for the use of such a hardware component (hereinafter called an "Outboard Data Manager - ODM") to provide a new, higher level I/O interface for system 370 CPUs.

The interface between the CPU and the ODM is a logical interface. The interface is logical in that the information passed by the CPU does not specify the physical location of the data being requested. The physical location of the data is the responsibility of, and is known only by, the ODM. The variables used by the CPU to identify the requested data are a Data Set Identifier and a Record Identifier.

The Data Set Identifier (DSID) is a unique six-byte binary number generated by the ODM when a data set is created. The operating system within the CPU retains this value and passes it to the ODM with each request involving the data set. The generation of the DSID is performed by the ODM rather than the CPU, in order to permit the ODM to be attached to multiple independent CPUs. The centralization of the generation function in the ODM guarantees uniqueness of DSIDs across multiple CPUs.

The Record Identifier (RID) is a six-byte binary number. This value is actually the logical name of a physical block within a data set. The generation of this value is under the control of the creator of the data set within the operating system.

The DSID and the RID are, therefore, the basic components of the ODM interface. The operating system within the CPU uses these values to communicate with the ODM via the following commands:
1) ASSIGN DSID

This command is issued by the operating system whenever it is

about to create a new data set. The ODM maintains a six-byte

DSID counter. Upon receiving this command, the ODM returns the

current value of the counter to the requestor and increments

the counter value by one.
2) SET DSID (-RID)

This command is used to establish a context for a subsequent

(through CCW command chaining) ATTRIBUTE, RETRIEVE, WRITE,

READ, or DELETE-RECORD command. The SET command identifies

the DSID to be associated with a ATTRIBUTE or RETRIEVE command.

It identifies the DSID and RID of the record to be read or

written by a subsequent READ or WRITE command.
3) ATTRIBUTE.

The ATTRIBUTE command is used by the operating system to pass

information about a data set (data set attributes) to the ODM.

The command is issued after a DSID for the data set has been

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assigned by the ODM (after an ASSIGN DSID has been done). The

data set with which the command is associated is identified by

the DSID value specified in the preceding...