1. Field of the Invention
The present invention relates to systems and methods for writing and reading data from computer disk drives, and in particular to a method and system for reading and writing data using a disk drive having independently controllable heads or arms.
2. Description of the Related Art
Disk and tape data storage devices are well known in the art. The data is stored as a plurality of data tracks of predetermined format disposed on a recording medium such as a magnetic disk, an optical disk, or magnetic tape. The data is written to and read from the tracks using one or more transducers or read/write heads, which are electrically coupled to signal processing electronics to provide a data transfer path between the media and a requesting system external to the storage device.
The heads are supported in close proximity to the media by a head positioning assembly capable of operating in two distinct modes: track seeking and track following. During track seeking, the heads are moved transversely to the tracks from a current data track to a desired or target track in response to a read or write request from the external system. Track following is the function of maintaining a head in alignment with a track while reading, writing, or merely idling.
In most storage devices, movement of the head positioning assembly is controlled by a closed loop servo system comprising a combination of servo electronics and microcode providing a signal to a voice coil motor (VCM) or similar device. Closed loop systems utilize position information obtained from the surface of the storage medium as feedback to perform the seeking and track following functions. Examples of closed loop servo control system are provided in commonly assigned U.S. Pat. Nos. 4,679,103 and 5,404,254, which applications are hereby incorporated by reference herein. Some disk drive designs hold servo information on a single, dedicated disk surface (i.e., dedicated servo). Other disk drive designs, and most tape drives, provide servo information embedded between the data regions of the storage media (i.e., embedded servo) in the form of a PES field. The PES field is written using an external positioning device known as a pusher or a servowriter, and read with a magnetoresistive read element. Unfortunately, because of manufacturing tolerances, the read and writing elements can vary in width, which can cause the sensed head position to vary non-linearly with the actual head position.
Servo information typically includes a track identifier and a burst pattern, which are combined to produce a position signal. Typical burst patterns are discussed in co-pending and assigned patent application Ser. No. 09/300,071, entitled xe2x80x9cPOSITION ERROR SIGNAL LINEARIZATION USING AN AUXILIARY DISCONTINUITY REMOVAL ROUTINE,xe2x80x9d by Jeff J. Dobbek, Gregory M. Frees, Craig N. Fukushima, Louis J. Serrano, and Markus Staudenmann, filed Apr. 27, 1999, which application is herein incorporated by reference.
The track identifier is commonly in the form of a grey code or track address and is used to uniquely identify the track currently beneath the transducer. The burst pattern produces an analog signal indicative of track type and head offset with respect to the center of the current track. If a quadrature burst pattern is used, the resulting analog signal is demodulated into primary (PESP) and quadrature (PESQ) signals. When the head moves transversely to the tracks during a seek operation, the track identifier and quadrature contributions are combined or xe2x80x9cstitchedxe2x80x9d together to ideally provide a linear position signal.
In recent years, some disk drive designs have incorporated multiple separately controllable heads. Such designs are described, for example, in U.S. Pat. No. 5,805,386, issued to Faris on Sep. 8, 1998, U.S. Pat. No. 5,761,007, issued to Price et al. on Jun. 2, 1998, and U.S. Pat. No. 5,343,347, issued to Gilovich on Aug. 30, 1994, which applications are hereby incorporated by reference. Other disk drive designs have incorporated multiple voice coil motors to control a single head. Examples of such designs are disclosed in U.S. Pat. No. 5,621,591, issued to Rahimi et al. on Apr. 15, 1997, and U.S. Pat. No. 5,781,381, issued to Kokanezawa et al., which applications are hereby incorporated by reference. Such designs can improve performance by allowing one of the heads to read information, while another head is moving to another track location.
To provide separately controllable heads, at least one VCM for each head is typically used. Typically, each VCM uses a twisted pair of wires to carry the servo and data signal from a preamplifier inside the drive to an electric card. As the number of VCMs increases, the number of signal lines increases as well. For disk drive designs with several VCMs, such multiple wires can be impractical and expensive. Further, the use of several wires requires additional preamplifier input/output (I/O) ports.
What is needed is disk drive design that can accommodate multiple VCMs while minimizing the number of required wires and contacts. The present invention satisfies that need.
To address the requirements described above; the present invention discloses a method, apparatus, and article of manufacture, for controlling a disk drive with multiple VCMs.
The apparatus comprises a first disk storage surface and a second disk storage surface. The first disk storage surface has a plurality of first data segments and a plurality of first servo track segments interspersed therebetween, and is readable and writeable by a first head controllable according to a first servo track signal read from at least one of the first servo track segments. The second disk storage surface has a plurality of second data segments and a plurality of second servo track segments interspersed therebetween, and is readable and writeable a second head separately controllable from the first head according to a second servo track signal read from at least one of the plurality of second servo track segments. The first and second servo track signals are distinguishable by a servo signal characteristic, which allows a single signal transmittable on a single wire to convey the required servo track information to all of the heads.
The invention describes a technique for providing a track signal for each of a plurality of separately-controllable disk drive heads, each servicing an associated disk storage surface having a plurality of data segments and servo track segments storing a servo track signal interspersed therebetween. The method comprises the steps of reading the disk storage surfaces with each disk drive head in parallel to generate a servo track signal for each head, wherein the servo track signal from each head is distinguishable from the servo track signal for other heads by a servo signal characteristic; and combining the servo track signals from each head into a single servo track signal. The article of manufacture comprises a program storage device, readable by a computer, tangibly embodying at least one program of instructions executable by the computer to perform method steps described above.