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Simulation of Magnetic Disk Defects by Off-Track Writing and Reading

IP.com Disclosure Number: IPCOM000039633D
Original Publication Date: 1987-Jul-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 3 page(s) / 69K

Publishing Venue

IBM

Related People

Horii, RR: AUTHOR [+2]

Abstract

The manufacture of high-performance magnetic disk storage devices requires careful testing of the disk surfaces for defects that could result in readback errors. A tester used for testing the disk surface writes different patterns on the disk and looks for distortions in the readback signal. Checking the function of this tester normally involves feeding in externally synthesized waveforms which simulate a disk surface with various types of defects. A method is described here which eliminates the need for external equipment to synthesize the test waveforms. This method uses off-track writing to generate amplitude- modulated patterns on the disk. The disk tester has the following inherent capabilities. It can move the read/write heads to any track and can move them off the center of the track in small increments.

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Simulation of Magnetic Disk Defects by Off-Track Writing and Reading

The manufacture of high-performance magnetic disk storage devices requires careful testing of the disk surfaces for defects that could result in readback errors. A tester used for testing the disk surface writes different patterns on the disk and looks for distortions in the readback signal. Checking the function of this tester normally involves feeding in externally synthesized waveforms which simulate a disk surface with various types of defects. A method is described here which eliminates the need for external equipment to synthesize the test waveforms. This method uses off-track writing to generate amplitude- modulated patterns on the disk. The disk tester has the following inherent capabilities. It can move the read/write heads to any track and can move them off the center of the track in small increments. It can write high-frequency or DC signals onto the disk in continuous patterns or short bursts. It can measure accurately the average amplitude of the readback signal. It detects surface defects by looking for short and long-term variations in the amplitude of the readback signal. A block diagram of the tester is shown in Fig. 1. The technique of simulating disk defects is based on the principle that if an AC pattern is written with the head positioned over the center of a track and the head is then moved slightly off track-center, the amplitude of the readback signal will be lower than if the head

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were reading on track-center. The further away from track-center the head is moved, the lower the amplitude of the readback signal. One type of disk defect that may be simulated is a negative modulation defect. This is manifested as a decrease in the amplitude of the readback signal below the average track amplitude. To simulate this, a full-track high frequency pattern is written on-track. A short segment is then erased at some location. The head is then moved slightly off-track. The erased segment is then overwritten with a high-frequency pattern. The head is moved on-track again. When the track is read back, the rewritten segment will be lower in amplitude than the rest of the track, simulating a negative m...