Browse Prior Art Database

High Speed Track Format Switching for Zoned Bit Recording

IP.com Disclosure Number: IPCOM000106604D
Original Publication Date: 1993-Nov-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 6 page(s) / 170K

Publishing Venue

IBM

Related People

Donaldson, JE: AUTHOR [+3]

Abstract

Inherent to fixed block DASD (Direct Access Storage Device) is a division of each disk into equally sized segments around the disk surface: these equal portions are referred to as Sectors. It is these individual Sectors of a pre-defined-size which contain Customer Data saved for later retrieval and updates. BDR (Banded Data Recording) is a technique used to increase the storage capacity of a file by creating bands of tracks containing different quantities of Sectors within a revolution.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 38% of the total text.

High Speed Track Format Switching for Zoned Bit Recording

      Inherent to fixed block DASD (Direct Access Storage Device) is
a division of each disk into equally sized segments around the disk
surface: these equal portions are referred to as Sectors.  It is
these individual Sectors of a pre-defined-size which contain Customer
Data saved for later retrieval and updates.  BDR (Banded Data
Recording) is a technique used to increase the storage capacity of a
file by creating bands of tracks containing different quantities of
Sectors within a revolution.

      With each transition across a band boundary, the track
format(sector placement) must change to reflect a new data rate and
the quantity of sectors.  This transition causes a delay in the
transmission of customer data and a significant adder to the overhead
of the command as the number of bands (thus the likelihood of needing
to cross a boundary on each command) increases.

      This idea, when used in conjunction with another invention,
reduces the delay associated with format switching.

      Two potential solutions are given.  Each with its own benefits.
The first deals with replication of hardware involved in the
generation of Sector pulses.  The second, with a shared
Microprocessor/hardware implementation.

      Option 'A' (Logic replication based solution) - This solution
is implemented by providing multiple and simultaneous generation of
Sector Pulse placements, each using a common digital correction of
the clock which generates the Sector Pulses; this correction is
determined based on the expected location of the individual Servo
IDentification fields located on the disk.

      The exact number of Sector Pulse Generators is dependent upon
the architecture of the file:  the number of bands being used,
limitations on the amount of logic, and the relationship of the
latency associated with seeking to the new cylinder.  The minimum
number necessary is three:  this covers the current band, and the 2
bands adjacent (on either size) to the current band.  The limitation
of this implementation is the possibility of latency resulting from a
seek beyond either adjacent band.

Note:  Using only 2 generators is possible if the file architecture
       is designed to use the elevator seek method of overlapped
       commands.  This method ensures that the majority of all seeks
       are in a single direction.

The maximum number of generators to be used is equal to the number of
bands within the file: one Sector Pulse Generator for each band.
Logical Blocks Diagram:

1.  Sector Pulse Select Control
    This multiplexor logic controls which Sector Pulse Generator
    output is sourced as the Sector Pulse.  The multiplexor also
    degates glitching of the Sector Pulse during transition between
    generators.

2.  Sector-to-Sector Counter
    This is a set of separate counters each based on a unique spacing
    value for...