Browse Prior Art Database

Medium Self-Description for Removable Medium Devices

IP.com Disclosure Number: IPCOM000114080D
Original Publication Date: 1994-Nov-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 8 page(s) / 315K

Publishing Venue

IBM

Related People

Ripberger, RA: AUTHOR

Abstract

A method of defining self-describing data about the device's supported media and formats and of exploiting this information in the program is described. The method removes certain program dependencies on having prior knowledge about the device's capabilities, facilitating migration to new hardware platforms with less or no programming modifications.

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This is the abbreviated version, containing approximately 14% of the total text.

Medium Self-Description for Removable Medium Devices

      A method of defining self-describing data about the device's
supported media and formats and of exploiting this information in the
program is described.  The method removes certain program
dependencies
on having prior knowledge about the device's capabilities,
facilitating
migration to new hardware platforms with less or no programming
modifications.

      In many control programs which support removable medium
devices, it is typical that the control program manages the selection
of devices for particular jobs which are to run on the system.  In
order to select an appropriate device, the program must know the
requirements of the job to be run (e.g., what medium type, what
medium format, etc.) and match these with the characteristics of a
device which is compatible with these requirements.

      Typically, when a new data set is created, the job makes its
requirements known through some Job-Control Language (JCL) or
Automatic Class-Selection (ACS) routine.  The requirements specify
things like a device type and perhaps a density code or recording
technique.  For existing data sets, the job may again specify its
requirements; or the control program (or related component) may save
this information when the data set is created so that it can be used
to allocate an appropriate device during a subsequent request for the
data set.

      When a new device type is defined, the program requires
beforehand knowledge about the device in order to determine whether
it is medium compatible with some other existing device types or
whether it supports a new incompatible medium.  This requirement
exists even if the device is in all other ways (e.g., as far as
communication with the program is concerned) identical to prior
devices.  In some cases, the device may in fact support multiple
medium types and multiple formats and the determination of the rules
for compatibility of media with the device must be coded into the
program.

      This dependency on control program support is an impediment to
the introduction of new devices and new medium types.  It would be
highly desirable to provide a mechanism whereby the program can be
written to determine the device's characteristics relative to
supported media without requiring beforehand knowledge and
programming modifications.

      A mechanism is proposed whereby the program can learn, from
information supplied by the device, the characteristics of the media
supported by the device or the characteristics of the medium
currently in use by the device.  Moreover, the program could use such
information to store the characteristics of a set of devices or of a
piece of medium used for a given dataset and subsequently use this
information to generalize the device selection process on subsequent
accesses to that same data set.  In addition, by providing additional
characteristics about the medium, job control languages (or ACS...