Computer Science

Magnetic Storage

Magnetic storage refers to the technology of storing data using magnetized materials, such as hard disk drives and magnetic tapes. In this method, data is encoded as magnetic patterns on the storage medium, allowing for non-volatile and relatively high-capacity storage. Magnetic storage has been a fundamental component of computer systems for decades, providing a cost-effective and reliable means of data storage.

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  • Computer Fundamentals - 8th Edition
    eBook - ePub

    Computer Fundamentals - 8th Edition

    Concepts, Systems & Applications

  • Backing up of data stored on an on-line storage device such as a disk, for its off-line storage. However, over time, tape will become more of an archive medium because users are increasingly using disk-based solutions to meet backup requirements.
  • Archiving of data used occasionally. Tape continues to be the preferred medium for data archival.
  • Transferring of data and programs between two computers not linked together.
  • Distribution of software. Vendors often distribute software products or their updates on magnetic tapes.
    • Figure 8.7. Illustrating the use of tapes in a sequential application.

    MAGNETIC DISKS

    Magnetic disks are the most popular direct-access secondary storage device. They are also the most popular on-line secondary storage device.
    A magnetic disk is a thin, circular plate/platter of metal or plastic. Its surfaces on both sides have a coating (such as iron oxide) that can record data by magnetization. Data is recorded on its coated surfaces as tiny, invisible magnetized and non-magnetized spots (representing 1s and 0s). It uses a standard binary code, usually 8-bit EBCDIC, for recording data. The disk itself is stored in a specially designed protective envelope, or cartridge, or several of them are stacked together in a sealed, contamination-free container.
    Like in the case of magnetic tapes, we can erase old data and record new data on magnetic disks as well. As we record new data on it, it erases old data in the same area automatically. However, we can read stored data many times without affecting it.

    Basic Principles of Operation

    Storage Organization

    A magnetic disk's surface has a number of invisible, concentric circles called tracks . Tracks have numbers consecutively from outermost to innermost starting from zero (see Figure 8.8 ). Number of tracks varies greatly, with low-capacity disks having as few as 40 tracks and high-capacity disks having several thousands tracks.
    A magnetic disk's surface also has invisible, pie-shaped segments (see Figure 8.9 ). Hence, if there are eight such segments, each track has eight parts. Each such part of a track is called a sector
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  • Cloud Computing
    eBook - ePub

    Cloud Computing

    Business Trends and Technologies

    • Igor Faynberg, Hui-Lan Lu, Dor Skuler(Authors)
    • 2015(Publication Date)
    • Wiley
      (Publisher)
    DAS, as the term implies, is directly attached to a processor through a point-to-point link. (The dominant technology in this case is the hard-disk drive.) In contrast, NAS and SAN reside across a network. This network is purpose-built for, and dedicated to, storage traffic in the case of SAN. One major difference between NAS and SAN lies in the semantics of the interface. The NAS units are files or objects, while the SAN units are disk blocks. Another key difference lies in the underlying transport. SAN relies on specialized transport, FC, which is optimized for storage traffic. NAS does not require anything special apart from the IP network. We will discuss the integration of both types of access after taking a closer look at the forms of storage.
    For now, we note that NAS and SAN are readily applicable to Cloud Computing but DAS has a limitation. An essential feature of Cloud Computing is flexible allocation of virtual machines based on, among other factors, resource availability and geographical location. In the DAS case, when a virtual machine moves to a new physical host, the associated storage needs to move to the same host, too, which is likely to result in consuming both much bandwidth and much time.
    Storage is further classified as online storage and offline storage. Online storage is accessible to a server, while offline storage, which is intended for archiving, is not. Magnetic tape libraries and optical jukeboxes are common implementations of offline storage. They usually come with automatic control via a robotic arm that can locate, fetch, mount, dismount, and put back a tape or disc. Google data centers, for example, have employed robotic tape libraries for backup.
    Besides magnetic tapes and optical discs, common storage media include magnetic disks and integrated circuits (i.e., solid-state electronics). Among these, magnetic hard disks are most prevalent.5
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  • Information Systems
    eBook - ePub

    Information Systems

    What Every Business Student Needs to Know, Second Edition

    • Efrem G. Mallach(Author)
    • 2020(Publication Date)
    • CRC Press
      (Publisher)
    At the enterprise level, solid-state storage can be used for frequently accessed files. Usually, most of any computer’s accesses are to a small set of files. Using solid-state storage for those, but magnetic drives for less frequently accessed files, provides most of the performance advantages of solid-state storage at a slight cost premium over a totally Magnetic Storage system.
    Some disk drive vendors sell hybrid drives that take advantage of this concept. Drive electronics monitor what data is used most, and put that data in solid-state storage for rapid access. This is based on usage statistics, not on knowledge of file content, so it can’t be planned as carefully as assigning files to different device types, but it is effective nonetheless.
    Because solid-state storage devices are light and don’t need sealed enclosures, they make excellent removable storage. Your flash drive is an example. So are your phone’s SIM card and your camera’s SD card. Their capacities increase rapidly each year, as their cost drops.
    The highest-capacity solid-state drive available today is the Nimbus Data ExaDrive DC100. Its 100 TB capacity exceeds that of the largest available rotating magnetic disk drives by a substantial margin. However, this capacity comes at a price: well into five figures. The same capacity, which would have to be spread over five or six drives, is available in magnetic disks for about $2,000. If one needs maximum capacity and performance, though, there is no current alternative. According to Nimbus, companies such as eBay have large amounts of their storage.
    Magnetic Tape Storage
    Magnetic tape , an older technology, is still used at the enterprise level though it is rare on personal computers. A modern tape cartridge that conforms to the 2017 LTO-8 standard, such as the one shown in Figure 3.14
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