Browse Prior Art Database

I/O Device Reservation

IP.com Disclosure Number: IPCOM000093822D
Original Publication Date: 1966-Mar-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Walker, D: AUTHOR [+2]

Abstract

Apparatus is shown in drawing A for allowing control of each input/ output device 10 by two data channels of CPU's 11. The apparatus in drawing B allows control of each input/output device by two file control units 21 and associated data channels or CPU's.

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I/O Device Reservation

Apparatus is shown in drawing A for allowing control of each input/ output device 10 by two data channels of CPU's 11. The apparatus in drawing B allows control of each input/output device by two file control units 21 and associated data channels or CPU's.

In either case, where the input/output devices 10 are random-access disk files, a problem arises when data is to be updated. This problem is that the file is released once the data to be updated is read and before it is rewritten. During this time, the other channel or CPU can acquire control of the file and drive the access arm to a different track. The original channel or CPU must then wait until it can regain control of the file. A second problem is that the other channel or CPU can gain control during the above interval and read the data being updated, thus acquiring erroneous data. This is a particularly important problem in the inventory control field.

The solution utilized in the apparatus of drawings A and B comprises control circuitry in the switch units 12 and 22 allowing reservation of a file. Two registers one for each CPU or channel, are provided for each file. Either CPU or channel can reserve a file by setting a bit into the appropriate register. Whenever the other CPU or channel subsequently tries to use the file, the control circuitry transmits a busy signal. Only the reserving CPU or channel can reset the appropriate register and thus relinquish its reservation of a file...