Browse Prior Art Database

Small Computer System Interface Disk Advanced BIOS Multi-Logical Identification

IP.com Disclosure Number: IPCOM000100888D
Original Publication Date: 1990-Jun-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 3 page(s) / 124K

Publishing Venue

IBM

Related People

Geisler, DR: AUTHOR [+5]

Abstract

A technique is described whereby multi-logical identification provides compatibility for disk device drivers to operate in advanced BIOS mode, as used in Personal Computer systems. An algorithm is used to determine the most efficient and compatible implementation of disk drive interrupts for operation in small computer system interface (SCSI) operations.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Small Computer System Interface Disk Advanced BIOS Multi-Logical Identification

       A technique is described whereby multi-logical
identification provides compatibility for disk device drivers to
operate in advanced BIOS mode, as used in Personal Computer systems.
An algorithm is used to determine the most efficient and compatible
implementation of disk drive interrupts for operation in small
computer system interface (SCSI) operations.

      The SCSI disk advanced BIOS (ABIOS) supports concurrent
operations of up to fifteen disk drives on one adapter. Typically,
disk ABIOS has assigned a single logical identification (LID) for all
drives on a single adapter.

      The single adapter has the ability to interrupt on a single
interrupt level.  The ABIOS is such that when an interrupt occurs on
a given level, each outstanding request that is waiting for an
interrupt on a given LID must be called to determine if it should
service that interrupt.

      For example, assume two disk drive units to a LID are operating
concurrently.  Assume a request has been issued to each drive unit
such that each has an outstanding request waiting for an interrupt.
When the interrupt occurs, each request must be invoked even if the
interrupt was actually serviced by the first request that was
invoked.  Also, assume that the number of units on the LID has been
increased to the maximum of fifteen and that a request has been
issued to each unit such that each unit has an outstanding request
waiting for an interrupt.  When the first interrupt occurs, even
though the interrupt might pertain to the first unit, each of the
fifteen interrupt routines, one for each unit, are called.  This is
considered a needless time-consuming operation that can downgrade the
performance of a multi-tasking operating system.

      At first glance, the solution to the problem could be to assign
one drive unit per LID.  In the above example, instead of having a
single LID with fifteen drive units, there would be fifteen LIDs, one
for each drive unit.  In this situation, when an interrupt occurs,
each of the interrupt routines is called until the interrupting LID
is serviced.  If the interrupt pertains to the first LID, the system
performance of the operating system is increased because only one
interrupt routine is called, as opposed to fifteen interrupt routines
in the above example. However, this approach has distinct drawbacks,
such as when an operating system implements support to only one disk
LID. In this case, support would occur only on one disk drive unit,
even though two drives actually exist.  This would be unacceptable.

      The concept applies to two types of disk LIDs.  The first type
of disk LID supports two disk units.  The ...