International Business Machines Corporation

Storage Technology Corporation

Mark G Call

Jonathan James Ashley

Paul H Siegel

Nelson K Arter

Geoffrey A Hungerford

Bradley E Whitney

Mark L Rhoades

The system for gap positioning optimization in a tape drive takes advantage of the presence of a pair of read heads, located one on either side of the write head, to precisely determine the boundary between the inter-block gap and the data blocks adjoining the inter-block gap. In particular, the servo mechanisms in the tape drive note the location of the boundary between the present data block and the inter-block gap formed a the end of the present data block. When the tape is repositioned between data read/write operations, this servo information is used to identify this boundary to initiate the subsequently received data read/write operation. A predetermined amount of inter-block gap is provided at the end of the data block to ensure that subsequently received data is not written on top of the present data block or the overwriting of the next data record begins at the beginning of the data block. The system for gap positioning optimization in a tape drive activates the upstream read head during the tape acceleration process to sense the location of this boundary. The upstream read head senses the presence of a region devoid of data, indicating the inter-block gap, thereby confirming the location of the boundary with more precision than the servo data indication, and positively verifying before the write operation that the selected block is the one desired.

System for gap positioning optimization in a tape drive

Encoding method for data to be recorded on optical disks using the pit-per-transition technique or return-to-zero techniques whereby the characteristics of the encoded bits produce a stable, low frequency spectral notch and minimum interference with associated focus and tracking servomechanisms. RLL (d,k) code words are selected so that the ratio of the lengths of pits and lands approximate some nonzero fraction less than one-half which depends on the (d,k) code employed. For example, a fraction of 1/3 is appropriate for RLL (2,7).

Encoding for pit-per-transition optical data recording

Error compensation in a feedback servo system. The feedback servo loop in, for example, a head positioning circuit in an optical disk data recording and retrieval system is provided with a compensation signal to correct for misalignment or other errors. The head in such a system must be dynamically maintained at a best focus position but, through use and transporting, the alignment of the head position error detecting system can be disturbed. In some cases, the loop circuit parameters may drift from their original values. To correct for errors introduced from such causes, the head is positioned at best focus and the focus error (head position error) signal is sensed. A correction signal is supplied which cancels out the sensed value while the system is operating.

Focus servo loop off-set compensation

A voltage-controlled oscillator (VCO) comprises a current controlled oscillator (ICO) and control circuitry which independently adjusts the gain (K.sub.v) and free-run or center frequency of the VCO. The control circuitry includes a first current source selected to set the free-run frequency of the VCO and a second current source selected to set the gain (K.sub.v) of the VCO. The current sources are coupled to a common node in a summing/difference configuration. The controlled current generated from the summing/difference configuration is delivered into the ICO. Independent current mirrors are utilized to supply controlled current into the node of the summing/difference configuration.

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Longmont, CO, United States of America

Mark G Call