Could future Apple TVs have DVD functions? A new Apple patent at the US Patent & Trademark Office hints that this could be the case, noting that “this technology could be aimed at a digital video recorder.” At the very least the patent shows that the long term future for all of Apple’s devices involves solid-state memory.
Patent number 20100268866 is for systems and methods for operating a disk drive. System and methods for storing data to a storage device are provided. In embodiments, the storage device may include a disk drive with a solid-state memory for storing certain frequently updated information. In some embodiments, the solid-state memory may be used to store journaling information. The inventor is Thomas R. Colligan.
Here’s Apple’s background and summary of the invention: “Hard disk drives continue to be one of the most widely used electronic storage mediums. Typically, a hard drive stores electronic data by storing a series of magnetic polarity transitions in circular tracks along the surface a magnetic disk. As disk drive technology has advanced, the amount of data that may be stored on a disk has greatly increased, in part, by increasing the density of the tracks. With increased track density, however, the risk of data corruption through adjacent track interference, often referred to as ATI, and wide area adjacent track erasure, often referred to as ATE, also increases.
“Adjacent track interference occurs during write operations when the fringing magnetic field of the head weakens the magnetic polarity transitions on tracks adjacent to the track being written. Over time, after successive write operations to a particular track, the data stored on the adjacent tracks may weaken to the point of becoming unreadable, resulting in corruption of the file and loss of data. Wide area adjacent track erasure poses a similar problem.
“In a typical perpendicular recording design, a soft underlayer is used in the media as part of the flux return path to enhance the write field, and a shield is added next to the write pole in the write head to increase the write field gradient. Unfortunately, the shield leads to an additional flux path, and the write coil induces flux through this additional path during writing, often resulting in adjacent track erasure. Given the large footprint of these shields, the erasure can occur over a fairly wide span, thus rendering the term wide area adjacent track erasure.
“Accordingly, modern disk drives often include correction algorithms designed to reduce the effects of ATI and ATE by periodically refreshing data before the data becomes unreadable. The refreshing process may involve reading particular tracks and re-writing the data in those tracks. These correction algorithms, however, may tend to reduce the performance of the hard drive by reducing the hard drive’s availability while the correction algorithms execute.
“To increase the efficiency of data correction algorithms, the algorithms may tend to target tracks that are in high traffic areas, i.e., areas of the disk that have experienced more write operations and, therefore, potentially higher levels of ATI and/or ATE. For example, the disk drive may keep a record of the number of write operations that each track has experienced, and when a particular track has experienced a threshold number of writes, the data correction algorithm may then be executed to refresh the adjacent tracks. It will be appreciated, therefore, that high traffic areas of the disk will tend to cause the initiation of data correction algorithms more frequently.
“One area of the disk that may experience particularly high traffic is the journaling area of the disk, which is used by the operating system’s journaling file system. A journaling file system is used to reduce the likelihood of file corruption in the event of a system crash during the writing of file data to the disk drive. In a journaling file system, changes are written to or logged into a journal, which is usually contained in a reserved space on the hard drive, before the changes are committed to the main file system.
“A journaling file system maintains a journal of the changes it intends to make ahead of time, so that after crash the recovery simply involves replaying changes from the journal until the file system is consistent. To increase the average speed of file storage, the space on the disk drive that is reserved for the journal is usually toward the outer circumference of the disk, where the data processing speed is faster. This process provides the advantage that, in the event of a system crash during a file update, at least one uncorrupted version of the file will exist.
“Due to the fact that the journal is written during every write operation to the disk, the journal will usually be a very high traffic area. As a high traffic area, the journal may tend to experience more ATI and/or ATE, and as a result, the data correction algorithms may tend to be initiated more often for the journal area compared to other areas of the disk.
“Certain disclosed embodiments provide a disk drive with a solid state memory, such as a flash memory, wherein the flash memory may be used to store frequently updated information, such as a database or journaling information. Storing the frequently updated information to the flash memory rather than to the disk may result in more efficient use of the disk drive. For example, storing the journaling information to the flash memory instead of the disk may eliminate a particularly high traffic area from the disk, resulting in fewer executions of the correction algorithms, which would otherwise consume disk drive resources. For another example, moving the journal off the disk drive frees up more space on the disk drive for regular file storage.
“Additionally, the disk space made available by the absence of the journal may include the higher speed memory at the outer tracks of the disk. In some embodiments, the journal may be stored to both the flash memory and the disk drive. In this way, the reliability of the drive may be improved by providing a second redundant journal. In this embodiment, the redundant journal may be saved toward the center of the disk, thus reserving the higher speed outer tracks for regular file storage. Furthermore, information stored in the solid state memory, e.g., the flash memory, may be moved to the disk in response to a sleep event and returned to the flash memory in response to a wake event.”
