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Browse Prior Art Database

Electronic File Protect System

IP.com Disclosure Number: IPCOM000084979D
Original Publication Date: 1976-Feb-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 3 page(s) / 72K

Publishing Venue

IBM

Related People

Chaloupka, JA: AUTHOR [+2]

Abstract

This control system prevents inadvertent overwrite or erase of data on a magnetic storage medium. The system is designed so that inadvertent overwrite/erase is prevented unless two independent failures occur simultaneously. The failures might be either from remote control signals or local (within the system itself).

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Electronic File Protect System

This control system prevents inadvertent overwrite or erase of data on a magnetic storage medium. The system is designed so that inadvertent overwrite/erase is prevented unless two independent failures occur simultaneously. The failures might be either from remote control signals or local (within the system itself).

The control system receives five input signals -- Data, Select A, Select B, Not Machine Power Fail, Fault Reset. Output from the system is the Write Fault indication passed back to a remote control and the writing of data with head 10. Select A and Select B are bipolar signals whereby both have to be present to initiate a write operation. In addition, Not Machine Power Fail must also be present to initiate a write operation. Local power failure in the system is monitored by the local power detect circuit 14. There must be Local Power Available to initiate a write operation.

The data line is not monitored for failure as a failure in the data line is only a data error, as opposed to an inadvertent write or erase condition. Fault Reset is not monitored, but it is AC coupled by coupling 16 so that the file protect system will not be reset if the Fault Reset is clamped to a level due to an error condition. In other words Fault Reset must be a transition signal in order to get through AC coupling 16.

In operation, data is written by head 10 when the write data switch 18 in write driver 12 receives data from a remote controller, input voltage from power supply switch 20, and current from current supply switch 22. Several logical operations are required in the protect system before voltage will be supplied from power supply switch 20 and current will be supplied from current supply switch 22.

First, the power supply switch 20 will be enabled only if the Select A signal is present and Local Power Available is indicated by the local owner detect 14. The write status switch 24performs an AND function and, if its conditions are satisfied, enables the power supply switch 20.

Second, the current supply switch 22 is enabled by the current switch fault degate 26. The degate 26 performs an AND function on the condition -- Gate B, Not Machine Power Fail, and Not Fault Internal. The Not Fault Internal is a feedback signal from the fault latch 28 via the inverter 30. If the file protect system has not detected a fault, then inverter 30 will have a signal level indicating no fault to the dega...