Browse Prior Art Database

Method for Addressing System Mounted Disk Drives

IP.com Disclosure Number: IPCOM000035703D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 3 page(s) / 33K

Publishing Venue

IBM

Related People

Glinski, DM: AUTHOR [+3]

Abstract

It is a requirement in computing systems containing multiple DASD (Direct Access Storage Devices) that each device be "addressed" to a specific location in the system. The address is a logically defined code that identifies each device to the system processor and allows that processor, through the DASD control card(s), to key data storage and retrieval to the correct DASD. Essentially, addressing becomes a data management tool for uniquely identifying any specific device.

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Method for Addressing System Mounted Disk Drives

It is a requirement in computing systems containing multiple DASD (Direct Access Storage Devices) that each device be "addressed" to a specific location in the system. The address is a logically defined code that identifies each device to the system processor and allows that processor, through the DASD control card(s), to key data storage and retrieval to the correct DASD. Essentially, addressing becomes a data management tool for uniquely identifying any specific device.

Addressing of DASD has historically been accomplished through the use of a set of small rocker switches (usually three in number and commonly located on the logic board mounted on the DASD itself). In this implementation, switch settings on each DASD represent the binary equivalent of the decimal numbers 0 through 7, and (by shorting land patterns on the card) communicate each DASD's unique address to an "addressing" module on the DASD card which, in turn, sends this information to the processor card over the data (SCSI) bus. Problems occur when this method is used:

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Switches must be individually set by the operator when the system is assembled (and by the user or Customer Engineer when the system is field upgraded with more DASD units or when a new DASD is installed due to a repair action). Time is consumed in looking up the correct setting, and the operation is subject to error. Switches are commonly located so they can be accessed from the side of the DASD. This requires room for access and restricts available mounting locations for additional hardware (in this case, a regulator card). Seemingly identical DASD units are really different due to the switch setting. If factory or field stock is pre-addressed (to simplify customer set-up, for example), each variation must be stocked as a separate part number.

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The method described below eliminates these problems. Internal cabling in the system chassis includes a signal (bus) cable with one port for each DASD and a power cable with one branch for each DASD. Individual power and signal connectors are mounted in a connector housing (one for each DASD that can be attached) to whic...