Browse Prior Art Database

Method of Queuing I/O Device Status in an I/O Channel

IP.com Disclosure Number: IPCOM000086673D
Original Publication Date: 1976-Oct-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Covington, RP: AUTHOR [+3]

Abstract

Disclosed is a solution to the problem of queuing input/output (I/O) device status, that is, of remembering the status of several I/O devices before software has had a chance to service them.

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

Page 1 of 1

Method of Queuing I/O Device Status in an I/O Channel

Disclosed is a solution to the problem of queuing input/output (I/O) device status, that is, of remembering the status of several I/O devices before software has had a chance to service them.

The problem of queuing I/O device status is a problem which must be solved by all I/O channels. In an I/O Channel, many devices may be operating concurrently, and when one completes its operation, information about that completion must be communicated to the program (software) controlling that device. This status information typically contains the data count of the operation just completed, whether any errors or exceptional conditions were encountered, and anything else which may pertain to the particular nature of the I/O device. It takes software a certain amount of time to interpret and act on this information. If several devices complete operations close together in time (a normal occurrence), software will fall behind and the information must be remembered somewhere in the system or it will be lost.

One type of data processing system, for example, solves this problem by requiring each device to remember its status in hardware at the device until software is ready for it. This is a simple solution, but not optimal for several reasons. First, the memory at the device is always going to be more expensive than the main memory of the system. Second, the device will either not be able to start a new operation while status from an old one is pending (at the cost of system throughput), or else it will probably have to be more complicated (at the cost of...