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Common Input/Output Driver for Concurrent Support of Internal and External Channel and Control-Unit Functions

IP.com Disclosure Number: IPCOM000118897D
Original Publication Date: 1997-Sep-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 4 page(s) / 56K

Publishing Venue

IBM

Related People

Halma, M: AUTHOR [+3]

Abstract

Traditionally, S/390* systems attach storage devices through external control units (Fig. 1). The Channel Subsystem (CSS) manages Input/Output (I/O) operations issued by processors and passes commands via a Channel-I/O Driver over an I/O bus to the channel, which then interacts with the control-unit. Note that the protocol between the control unit and the Device Controller is very different from the one used between the Channel I/O Driver and the channel itself.

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This is the abbreviated version, containing approximately 97% of the total text.

Common Input/Output Driver for Concurrent Support of Internal and
External Channel and Control-Unit Functions

      Traditionally, S/390* systems attach storage devices through
external control units (Fig. 1).  The Channel Subsystem (CSS) manages
Input/Output (I/O) operations issued by processors and passes
commands via a Channel-I/O Driver over an I/O bus to the channel,
which then interacts with the control-unit.  Note that the protocol
between the control unit and the Device Controller is very different
from the one used between the Channel I/O Driver and the channel
itself.

      Integrating channel and control-unit functions into the Central
Processor Complex (CEC) would require a second I/O driver handling
the Device Controller protocol on the I/O Bus.

      By means of a switch placed between the Channel Subsystem and
the Channel I/O Driver in the CEC (Fig. 2), no dedicated I/O driver
is required and the Channel I/O Driver can be re-used.  The
combination of Channel I/O Driver and switch is called "Common I/O
Driver".

The approach has several advantages:
  o  re-use of existing code
  o  co-existence of internal and external storage attachments
      on same bus
  o  no impact to complex functions like the "Channel Subsystem"
      and the "Channel I/O Driver"
  o  same initialization, configuration and maintenance concept
      for internal and external storage attachment scheme
  o  lower development cost, shorter "time to...