Browse Prior Art Database

Rotational Position Identification

IP.com Disclosure Number: IPCOM000046309D
Original Publication Date: 1983-Jul-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 3 page(s) / 61K

Publishing Venue

IBM

Related People

Iskiyan, JL: AUTHOR [+3]

Abstract

Direct-access storage devices (DASDs), also referred to as disk files, can have a cache buffered system which operates with the DASD independent of the coupled host processor. In updating a record in place upon a track that has an image of the data in the cached system, the rotational position of the record must be accurately identified. In later model DASDs, each record track has internal rotational position indicators. Some of the lower capability and older DASDs have no such rotational position indicators. Accordingly, a programmed or microcoded method of precisely locating an access point for updating a record in place on a record track is provided. The DASD data in the cache system is usually compressed, i.e, the gaps are eliminated.

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Rotational Position Identification

Direct-access storage devices (DASDs), also referred to as disk files, can have a cache buffered system which operates with the DASD independent of the coupled host processor. In updating a record in place upon a track that has an image of the data in the cached system, the rotational position of the record must be accurately identified. In later model DASDs, each record track has internal rotational position indicators. Some of the lower capability and older DASDs have no such rotational position indicators. Accordingly, a programmed or microcoded method of precisely locating an access point for updating a record in place on a record track is provided. The DASD data in the cache system is usually compressed, i.e, the gaps are eliminated. Once the record is identified, the DASD data in the cache is parsed from which the actual physical displacement of the record from the index point of the track can be calculated,
i.e., gap lengths are known. The displacement D is calculated in terms of cell or byte positions along the track. From this number, the number of sectors, i.e., rotational portions of the disk, is calculated. Generally, the calculation will result in an integral number of sectors up to sector "N" with a small residue. The small residue is converted into time displacement and a timer is set on reaching the last sector N for interpolating between the sector marks on the track. When the timer has timed out, the record area is accessed.

A host processor accesses a cached DASD storage system through location processing which is data format related. The cached DASD storage system should operate independently of internal data formats for permitting a relatively loose coupling between the host processor and the storage system. The storage system includes a programmed control such as a microprocessor control store and working store with suitable other circuits, as is well known. Programmed in the control is a timer which has the capability of timing the actual elapsed time between two sector points as a disk in a DASD rotates past a transducer (not shown). Images of the data stored on DASD are selectively stored in the cache which includes a random-access memory, a directory in a hashing mechanism. The cached or data stored in the cached system is in compressed form, i.e., a continuous set of bits deleting all gaps in the DASD track for conserving cache storage space. The DASD data is otherwise related to the format on the DASD such that the index mark of the track is readily identifiable. When the programmed control determines that a record of a given track is to be updated in pl...