Digital Equipment Corporation

Bernardo Rub

Lih-Jyh Weng

Michael D Leis

John Edward DeRoo

Robert C Frame

Russell W Brown

William D Lewis

Fernando A Zayas

Elmer C Simmons

Norman A Field

Kenneth F Veseskis

Michael J Muchnik

Lih J Weng

Vinay K Aggarwal

Matthew F Giovanetti

Anne Solli

Samuel B Skraly

A method and apparatus for writing and reading servo data placed on a plurality of disk surfaces to minimize the degree of overlap of headers written or read by each write/read channel. Time division de-multiplexing (selecting) the writing of servo data to disk surfaces from each write/read channel and time division multiplexing the reading of servo data from the staggered headers contained on the disk surfaces coupled to each write/read channel increases the number of surfaces written to or read in a single rotation by each write/read channel. Disk surfaces are coupled to the write/read channels in groups to minimize the number of rotations required to write to or read from all the surfaces contained in the groups. Groups of surfaces may be sub-grouped. The headers of sub-groups are interleaved so that portions of the header written in a separate disk pass whose length is less than half the total length of the header may be written or read in the same rotation as another group of surfaces.

Method and apparatus for writing or reading servo information

A method and apparatus for optimizing the track seeking operation of disc drives by adaptively changing the seek velocity profile in response to the actual performance of the drive during track seeking operations based upon the amount of head overshoot and the actuator power dissipation.

Adaptive track seeking for disk drives

A data processing system records information on magnetic disks in a format in which sector headers, which include embedded servo information, are radially aligned and recorded at a single frequency and data are recorded at various band-related frequencies. The system records sector headers at a frequency which is optimal for the recording of address information in the shortest sector and records the data at frequencies which are optimal for the recording of information in the disk space allocated to the data portion of the various lengths of sectors. The system synchronizes to the headers, using conventional embedded servo synchronization methods, and produces header timing signals. It can then use the same header timing signals to locate and interpret the headers on different tracks, since the header frequency and the location of the headers are the same in every track. The system may record the data portions of the sectors at frequencies which are related to the header frequency by ratios of small integers. The system then uses, in synchronizing to the disk, a phase locked loop which includes a voltage controlled oscillator (VCO) that is driven to a reference frequency which is directly related to the header frequency. The system divides-down the frequency of the VCO output signal to produce the timing signals for the header. Also, it uses a version of the output signal of the VCO, which is divided-down by a band-related value, as a timing signal for the data.

Embedded servo banded format for magnetic disks for use with a data

A data decoding circuit which receives an input signal comprising a sequence of pulses and generates a digital data output signal and timing signals in response thereto. The circuit includes a phase-locked loop which generates timing signals in response to the input signal and an offset signal from a data separator circuit. The data separator circuit generates the digital data output signal and the offset signal, which measures the degree of correlation between the input signal as received by the data separator and the timing signal from the phase-locked loop, thereby obviating the need to match the data separator circuit closely to the phase-locked loop.

Data decoding circuit including phase-locked loop timing

A data decoding system includes a data retrieval device which retrieves encoded data from a mass-storage device and transmits the data to a serial-to-parallel shift register. The shift register, operating at the data transfer rate, converts the encoded data to a parallel stream of bit-pairs. The bit-pairs are then transmitted, over parallel lines, to a second shift register which is operating at one-half the data transfer rate. The second shift register stores a sufficient number of the bit-pairs to constitute a byte of binary data when decoded. Once enough bit-pairs are stored, a ROM, operating at a rate which is slower than the data transfer rate, decodes the information to form a byte of binary data. The system utilizes a data retrieval system with a high data transfer rate and processing circuitry with a reduced bandwidth requirement to produce decoded data at a rate which is comparable to the data transfer rate.

Improved decoder

The invention encodes magnetic disk sector addresses using a large distance, 'd', Reed-Solomon code to produce code words which vary by at least 'd' symbols for any two different encoded addresss. The result of the encoding is a set of redundancy symbols, which are usually associated with error correction. These symbols are appended to the address symbols to produce address code words. An address code word read from a disk can contain up to (d-1)/2 errors and still be identified as the correct sector address. To protect the encoded sector address from synchronization errors the address code words are further encoded by adding them to a coset leader to produce header code words. The header code words are then recorded in the address portions of the sectors. When a header code word is read from a sector, the coset leader is subtracted from the header code word to produce an address code word. The address code word is then compared with the address code word for the specified address. If there is a synchronization error, the comparison of the resulting address code word with the address code word for the specified address will result in a difference of more than (d-1)/2 symbols and the sector will not be treated as the specified address.

Method and apparatus for encoding magnetic disk sector addresses

The present invention provides translation circuitry, which in one mode of operation acts to encode variable length data words into fixed rate data coded words for use with a communication channel, or a recording means, such as a magnetic recording medium and which in another mode of operation acts to decode the coded words to data words. The translation circuitry functions such that in an encoding operation, the second and third bits of a three-bit coded word respectively have the same binary values as the first and second bits of the data word, which the coded word represents and the second and sixth bits of a six-bit coded word respectively have the same binary values as the third and fourth bits of the data word which the coded word represents.

Arrangement for encoding and decoding information signals

The present invention includes a first input signal circuit to receive pulse signals from a voltage-controlled oscillator (VCO), or some other controllable pulse signal source, and a second input signal circuit to receive pulse signals from a magnetic recording medium, or some pulse signal source, with which the voltage controlled oscillator is to be put in phase synchronization. A correction signal generator circuit is connected to both the input signal circuits to provide a first correction signal in response to a pulse signal from the recording medium and to provide a second correction signal in response to a pulse signal from the VCO. There is a third circuit which monitors how long a correction signal is in effect and if such a correction signal is present for longer than a predetermined time, the third circuit terminates the correction signal to enable a new correction signal to be generated in response to the next one of said input signals to arrive. Finally, there is a fourth circuit which is connected to the correction circuitry to permit it, in a first mode of operation, to be enabled at all times to phase correct the controllable pulse signal source in response to a predetermined pattern of signals from the recording medium and to permit it, in a second mode of operation, to be available only during 'window' periods initiated by pulse signals from the recording medium.

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Shrewsbury, MA, United States of America

Bernardo Rub