SKEW-AWARE DISK FORMAT FOR ARRAY READER BASED MAGNETIC RECORDING | Patent Publication Number 20150170676
US 20150170676 A1Agere Systems Broadcom
A method of reading data in a multi-reader two-dimensional magnetic recording system includes determining a position of a multi-reader head, selecting a mode for reading the data of a magnetic recording medium as a function of the position of the multi-reader head, and reading the data of the magnetic recording medium in the selected mode.
- 1. A method of reading data in a multi-reader two-dimensional magnetic recording system, the method comprising:ndetermining a position of a multi-reader head;selecting a mode for reading the data of a magnetic recording medium as a function of the position of the multi-reader head; andreading the data of the magnetic recording medium in the selected mode.
- 12. A system for enhancing read performance in a multi-reader two-dimensional magnetic recording system, the system comprising:na multi-reader head;a detection device detecting a position of the multi-reader head;a memory device storing a zone table; anda read channel configured to select a mode for reading data from a magnetic recording medium as a function of a mode selected from the zone table corresponding to the position of the multi-reader head.
- 19. A computer program product embodied in a non-transitory machine-readable medium having machine-readable program code embodied thereon for performing a method of reading data in a multi-reader two-dimensional magnetic recording system, the method comprising:ndetermining a position of a multi-reader head;selecting a mode for reading the data of a magnetic recording medium as a function of the position of the multi-reader head; andreading the data of the magnetic recording medium in the selected mode.
This application claims the benefit of U.S. Provisional Patent Application No. 61/916,789 filed on Dec. 16, 2013, the complete disclosure of which is expressly incorporated by reference herein in its entirety for all purposes.
The present invention relates generally to electrical and electronic circuitry, and more particularly relates to reading and writing a magnetic recording in a system having multiple sensors.
The magnetic disk drive recording industry continues to pursue advances in technology that will sustain enhancements in recording density in a cost-effective manner. Two approaches currently under investigation are bit patterned media recording (BPMR) and heat-assisted magnetic recording (HAMR). An objective of these approaches is to overcome challenges posed by the super-paramagnetic limit that imposes a trade-off among three fundamentally competing recording parameters: media signal-to-noise ratio (SNR), writability, and thermal stability. BPMR and HAMR, however, require modifications to the media and heads, which significantly increase costs. Another technology, two-dimensional magnetic recording (TDMR), which uses conventional media and a new multiple-head configuration, relies on powerful signal processing in an attempt to achieve a theoretical limit of one bit-per-grain recording density.
As a practical near-term milestone, array-reader based magnetic recording (ARMR) has been proposed to increase areal density with an array-reader and associated signal processing.
In accordance with an embodiment of the invention, a method of reading data in a multi-reader two-dimensional magnetic recording system includes determining a position of a multi-reader head, selecting a mode for reading the data of a magnetic recording medium as a function of the position of the multi-reader head, and reading the data of the magnetic recording medium in the selected mode. Other embodiments of the invention include, but are not limited to, being manifest as a TDMR read circuit fabricated as part of an integrated circuit, a method for improving read performance of a magnetic disk, and an electronic system. Additional and/or other embodiments of the invention are described in the following written description, including the claims, which is to be read in connection with the accompanying drawings.
The following drawings are presented by way of example only and without limitation, wherein like reference numerals (when used) indicate corresponding elements throughout the several views, and wherein:
It is to be appreciated that the drawings described herein are presented for illustrative purposes only. Moreover, common but well-understood elements and/or features that may be useful or necessary in a commercially feasible embodiment may not be shown in order to facilitate a less hindered view of the illustrated embodiments.
Embodiments of the invention will be described herein in the context of illustrative array-reader based magnetic recording (ARMR) systems for use, for example, in a data storage application. It should be understood, however, that embodiments of the invention are not limited to these or any other particular ARMR arrangements. Rather, embodiments of the invention are more broadly applicable to techniques for improving read performance of a magnetic storage device. In this regard, embodiments of the invention provide an apparatus and methodology for beneficially mitigating an impact of skew angle and cross-track separation (CTS) between readers in an ARMR system by switching of an array-reader mode for different skew zones. Moreover, it will become apparent to those skilled in the art given the teachings herein that numerous modifications can be made to the illustrative embodiments shown that are within the scope of the claimed invention. That is, no limitations with respect to the embodiments shown and described herein are intended or should be inferred.
As a preliminary matter, for purposes of clarifying and describing embodiments of the invention, the following table provides a summary of certain acronyms and their corresponding definitions, as the terms are used herein:
As previously stated, one problem with bit patterned media recording (BPMR) and heat-assisted magnetic recording (HAMR) is that these approaches require substantial modifications to the media and heads, which significantly increases costs. ARMR is seen as an intermediate approach between current perpendicular magnetic recording (PMR) and two-dimensional magnetic recording (TDMR), which provides a significant increase in storage density compared to PMR while avoiding the challenges posed by BPMR and HAMR. ARMR uses standard media and an array of read-elements, also referred to herein as a multi-reader head, in conjunction with changes in read-back signal processing to achieve improved signal-to-noise ratio (SNR) of a track that is being read (ARMR-MISO) or multiple tracks that are jointly read (ARMR-MIMO).
ARMR achieves an areal density gain by employing multi-dimensional joint signal processing of multiple read-back signals from the array reader. Embodiments of the invention are shown and described herein in the context of a multi-reader head including two read-elements (i.e., readers) that are positioned according to a prescribed CTS and down-track separation (DTS). Due to skew, among other factors (e.g., temperature, vibration, etc.), the effective CTS between readers varies. Further, the larger the DTS between read-elements without skew, denoted by DTS0 or d, the more the CTS will vary with skew. This is illustrated in
TDMR is a known recording architecture intended to support storage densities beyond those of conventional recording systems. TDMR utilizes multiple read-elements to read from multiple adjacent tracks and uses joint signal processing and detection to decode the signal from a target track. The gains achieved from TDMR come primarily from more powerful coding and signal processing algorithms that allow data bits to be stored more densely on a magnetic storage medium (e.g., disk). In traditional disk architectures with a single read-element, reading a single sector with TDMR generally involves reading the sectors on adjacent tracks, requiring additional disk rotations. To circumvent this problem, TDMR disk drives may use multiple read-elements, also referred to as a multi-reader head, on the same support arm, typically referred to as a slider, thus restoring traditional read service times through ARMR processes. One disadvantage of using a multi-reader approach is that multiple readers are reading different off-track locations due to the CTS varying with skew. Although manufacturers may provide the physical distances between the multiple read-elements, actual CTS between the read-elements can vary based on the skew angle of the multi-reader head to the data track and several other factors. The factors that may affect CTS include, but are not limited to, environmental factors, such as, for example, temperature and mechanical vibration, as well as manufacturing factors, such as, for example, skew between the slider and the disk surface, and alignment of the read-elements relative to one another and/or to the slider, among other factors.
Turning to
From
Here, a small θ can be between about −16 degrees and +16 degrees. In another embodiment, the range of θ is between about −16 degrees and +20 degrees. It is to be appreciated, however, that embodiments of the invention are not limited to any specific angle or range of angles. Different hardware (e.g., disk platters and read-elements) can have different ranges.
These variations in CTS for a given multi-reader head can result in different conditions at different skew angles, including a multiple input single output (MISO—1× out) condition (i.e., multiple read-elements disposed over the same track), and a multiple input multiple output (MIMO—2× out) condition (i.e., multiple read-elements disposed over different tracks).
According to exemplary embodiments of the invention, the read hardware switches between a multiple input single output (MISO) mode and a multiple input multiple output (MIMO) mode as a function of the skew angle θ or resulting CTS(θ). Here, MISO mode refers to a condition where multiple readers are disposed over one track to recover data from that track, and MIMO refers to a condition where multiple readers are disposed over multiple tracks to recover data from more than one track.
As shown in
In another example, at CTS=2 TP, a 1× throughput (corresponding to the MISO mode) can be achieved. As can be seen from
Depending upon a number of readers, CTS and DTS among individual readers, and the skew angle, different zones on the medium can be independently optimized for throughput and capacity. This also means different signal-to-noise-ratio (SNR) versus throughput for different zones. Embodiments of the invention, therefore, utilize switching of an array-reader mode for different skew zones as a function of CTS between readers to provide additional performance and/or areal density gains. Furthermore, one or more embodiments of the invention target different zones on the medium to serve different applications, which can have different requirements. These requirements can correspond to throughput and capacity. It is to be understood that embodiments of the invention are not limited to any specific CTS.
Exemplary embodiments of the invention improve overall disk drive performance with a two reader ARMR through kilo-bits per inch (kBPI) (a measure of linear recording density) and kilo-tracks per inch (kTPI) (a measure of track density) push at an outer peripheral region (OD region/large area), increasing overall per platter areal density significantly. It is to be understood that embodiments of the invention are not limited to any specific number of readers.
Exemplary embodiments of the invention enable channel optimization for each of the different zones. Since the usage mode of the channel is different in different zones, the disk format (e.g., track density, linear density) is tailored for the different zones. Since an effective channel sensed by an array-reader changes in each zone because of skew, optimization of an equalizer and PR target zone-wise become important. Different structures of an equalizer (e.g., an equalizer configured for 2D equalization and joint-track equalization) and corresponding target and detector will be required in zones having different throughputs (e.g., from 1× to 2× throughput).
Exemplary embodiments of the invention determine a zero-skew zone of the platter for increasing disk capacity. Referring to
1) High capacity region OD to MD at 1× throughput: Joint equalization of two reader outputs to detect one track;
2) Modest capacity region around MD at 1× throughput: Joint equalizer configured to operate as an inter-track-interference canceller to detect one track; and
3) Low capacity region around ID at 2× throughput: Joint equalizer and joint detector to detect two tracks.
Referring now to
At block 602 of
In one embodiment, the read channel 102 of
In
In one exemplary embodiment, determining the position at block 711 includes determining at which track(s) the multi-reader head disposed. It should be understood that the position can be determined by other methods (i.e., other than by track), including by region, skew angle, relative to a diameter of the magnetic recording medium, etc.
In one or more embodiments, the position of the multi-reader head is adjusted at block 713 to locate one or more of the readers within one or more tracks of the magnetic recording medium according to the selected mode. For example, in a case where the CTS of two readers of the multi-reader head is 1.5, only one track may be read using one reader. In this case, a 1× mode is selected based on the determination of the CTS using the zone table. Further, based on the selection of the 1× mode, the position of the multi-reader head is adjusted to locate the one reader of the multi-reader head in an approximate center of a corresponding track, while the remaining reader is allowed to be located at an approximate overlap of two adjacent tracks given the CTS of 1.5 (or without concern for its position) (essentially as shown in 406,
It should be understood that the adjustment of the position of the multi-reader head based on the mode selection at block 713 is optional. Furthermore, it should be understood that the values used in the example are not intended to be limiting and that these values are only used for describing exemplary aspects of the invention.
As will be appreciated by one skilled in the art, embodiments of the present invention may be implemented as an apparatus, system, method or computer program product. Accordingly, aspects of the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to as a “circuit,†“module†or “system.†Furthermore, embodiments of the present invention may take the form of a computer program product embodied in one or more non-transitory machine-readable medium(s) having machine-readable program code embodied thereon.
The block diagrams in the figures depict illustrative architectures, functionality, and operation of implementations of systems, methods and computer program products according to embodiments of the present invention. In this regard, each block shown in the block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing specified functions. It should also be noted that, in one or more embodiments, functions represented by the blocks may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be appreciated that each block of the block diagrams, and combinations of blocks in the block diagrams, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.
It should be understood that any of the methods described herein can include an additional step of providing a system comprising distinct software modules embodied on a non-transient computer-readable storage medium; the modules include, in one or more embodiments, any or all of the elements depicted in the block diagrams and/or described herein; by way of example and not limitation, a position determining module determining a position (e.g., track) of a multi-reader head (see for example, block 711,
In any case, it should be understood that the components illustrated herein may be implemented in various forms of hardware, software, or combinations thereof; for example, application specific integrated circuit(s) (ASICS), functional circuitry, one or more appropriately programmed general purpose digital computers with associated memory, and the like. Given the teachings of the invention provided herein, one of ordinary skill in the related art will be able to contemplate other implementations of the components of the invention.
In an integrated circuit implementation of one or more embodiments of the invention, multiple identical die are typically fabricated in a repeated pattern on a surface of a semiconductor wafer. Each such die may include a device described herein, and may include other structures and/or circuits. The individual dies are cut or diced from the wafer, then packaged as integrated circuits. One skilled in the art would know how to dice wafers and package die to produce integrated circuits. Any of the exemplary circuits illustrated in the accompanying figures, or portions thereof, may be part of an integrated circuit. Integrated circuits so manufactured are considered part of this invention.
The illustrations of embodiments of the invention described herein are intended to provide a general understanding of the structure of various embodiments, and they are not intended to serve as a complete description of all the elements and features of apparatus and systems that might make use of the structures described herein. Many other embodiments will become apparent to those skilled in the art given the teachings herein; other embodiments are utilized and derived therefrom, such that structural and logical substitutions and changes can be made without departing from the scope of this disclosure. The drawings are also merely representational and are not drawn to scale. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.
Embodiments of the invention are referred to herein, individually and/or collectively, by the term “embodiment†merely for convenience and without intending to limit the scope of this application to any single embodiment or inventive concept if more than one is, in fact, shown. Thus, although specific embodiments have been illustrated and described herein, it should be understood that an arrangement achieving the same purpose can be substituted for the specific embodiment(s) shown; that is, this disclosure is intended to cover any and all adaptations or variations of various embodiments. Combinations of the above embodiments, and other embodiments not specifically described herein, will become apparent to those of skill in the art given the teachings herein.
The abstract is provided to comply with 37 C.F.R. §1.72(b), which requires an abstract that will allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the appended claims reflect, inventive subject matter lies in less than all features of a single embodiment. Thus the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as separately claimed subject matter.
Given the teachings of embodiments of the invention provided herein, one of ordinary skill in the art will be able to contemplate other implementations and applications of the techniques of embodiments of the invention. Although illustrative embodiments of the invention have been described herein with reference to the accompanying drawings, it is to be understood that embodiments of the invention are not limited to those precise embodiments, and that various other changes and modifications are made therein by one skilled in the art without departing from the scope of the appended claims.