Browse Prior Art Database

Look-Ahead Mode Switching

IP.com Disclosure Number: IPCOM000100384D
Original Publication Date: 1990-Apr-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 1 page(s) / 30K

Publishing Venue

IBM

Related People

Berger, BH: AUTHOR [+3]

Abstract

When branching one track, such as track N, to the cache store in multi-track processing, it becomes necessary at times for the device process to note at index processing which mode should be taking place, either device processing or cache processing. If the data on track N+1 resides in the cache in a modified state, the mode must be changed to retrieve the data from the cache store to maintain data integrity.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 100% of the total text.

Look-Ahead Mode Switching

       When branching one track, such as track N, to the cache
store in multi-track processing, it becomes necessary at times for
the device process to note at index processing which mode should be
taking place, either device processing or cache processing.  If the
data on track N+1 resides in the cache in a modified state, the mode
must be changed to retrieve the data from the cache store to maintain
data integrity.

      One solution is to maintain a map of each cylinder bit of the
cache track images to indicate which tracks have modified data.  This
would require a channel command retry at index processing and
hardware to maintain these control structure maps.  Multiple
directory read operations would be required in order to maintain the
bit maps.

      A mode switch is made to determine whether the switch is
required from device processing to cache processing when modified
data resides in cache.  The condition of track N+1 is determined
concurrently with the data transfer for track N.  While the device
process is transferring fields to the cache, the state of track N+1
is determined if the track resides in cache and contains modified
data.  The decision is made during index processing whether to
continue as a device process or to switch to a cache process.