Browse Prior Art Database

Disk File Test Equipment

IP.com Disclosure Number: IPCOM000087797D
Original Publication Date: 1977-Mar-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 27K

Publishing Venue

IBM

Related People

Blythin, P: AUTHOR

Abstract

The recording density of present-day disk files is so high that even small defects in the disk surface can give rise to read errors. Accordingly, it is essential to test all disk surfaces before installation to determine the incidence of these errors and to reject the disk if the error rate is above a predetermined level. The test apparatus is shown in Fig. 1.

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Disk File Test Equipment

The recording density of present-day disk files is so high that even small defects in the disk surface can give rise to read errors. Accordingly, it is essential to test all disk surfaces before installation to determine the incidence of these errors and to reject the disk if the error rate is above a predetermined level. The test apparatus is shown in Fig. 1.

A continuous high-frequency square-wave simulating data, supplied from oscillator 1, is recorded by record/playback head 2 on a surface of a continuously rotating recording disk 3. On subsequent playback an error detection circuit 4 detects degraded read pulses resulting from disk defects. Error pulses corresponding to these degraded read pulses are sent by the detection circuit to a computer 5 where they are counted and their position on the disk surface logged. In order to detect these errors, an amplitude threshold circuit forming part of the detection circuit 4 must be accurately preset so as to detect all pulses having an amplitude below a certain level which are regarded as errors. Disk production yields depend critically on the setting accuracy of this detection circuit and necessitates setting tolerances of better than 2% in a factory environment. The apparatus shown in Fig. 2 enables the threshold circuit of the detection circuit to be accurately set even in the presence of noise.

The operation of the apparatus shown in Fig. 2 is based upon the assumption that if the threshold circuit is accurately set at the desired threshold then the presence of completely random noise will on average cause half of the errors to be detected and half of them to be missed. The apparatus consists therefore of an error simula...