Hard disk storage is quite different from magnetic tape, though both are often used for backup solutions. Both technologies operate on the same basic principles, which have been in use for over 60 years. The benefits and pitfalls of each make them best suited to different situations, however.
Basics of Magnetic Storage
On any magnetic storage medium, information is encoded into binary, then recorded by setting the polarity of many tiny regions on the media. This pattern of positives and negatives is a relatively resilient form of non-volatile memory and forms the basis for the majority of digital information storage. The size of the regions are only limited by the technology of the read and write mechanisms, and they have become much smaller in recent years. This allows more data to fit in the same space, which means more storage on hard drives and tapes without changing their physical dimensions.
Hard Drives
A hard drive operates like a group of record players stacked on top of each other. Several platters spin on a common spindle, and an arm moves to place read/write devices--the heads, analogous to turntable cartridges--over specific parts of each platter to read or change polarities of portions (sectors) of the platter.
The platter is typically made of glass or a non-magnetic alloy, coated with a thin layer of a ferromagnetic material. The platter is spun at very high speeds (up to 10,000 rpm), and the common arm moves to give the heads access to almost every part of the platter.
Unfortunately, the mechanical nature of hard drives makes them prone to failure, and data loss is not uncommon.
Tape Drives
Digital tape has been in use for over 50 years, and it remains a very common storage solution. Modern tape solutions use interchangeable tape cartridges in a fixed tape drive and often use a mechanical loader to automate cartridge switching.
Like a hard drive, positive and negative charges are written to a magnetized medium. In a digital tape, that medium is a half-inch wide magnetized ribbon. Blocks of data are stored in contiguous regions on the tape, but finding the desired region to read data back can take a lot of winding. Tape drives wind backward and forward automatically to find the requested data, but wait times can still be upward of 60 seconds. Modern tape drives can deliver 80 megabytes per second once transfer begins, however.
Digital tape is the most inexpensive mass storage medium, and for this reason it is still in widespread use for mass data operations. It is also less prone to mechanical failure and data loss than hard drives, but the extreme access time is a major issue with many implementations.
Common Uses: Hard Drives
Hard drives have the advantage of fast data seek times, and though the cost per byte is not as low as that of digital tapes, it is low enough for many purposes. Hard disks are most commonly used as the primary storage for computers, but they are also often used as backup media. The failure rate of hard drives is too high however, for a single drive to serve as an adequate failsafe. Many organizations connect multiple hard drives together in a RAID array for redundancy, or simply keep a second hard drive as a backup of their backup.
Modern hard drives are available as large as 2 terabytes, enough for many backup needs. This is an economical data storage solution for most users, but not necessarily a good long term one.
Common Uses: Tape Drives
Tape drives are the most inexpensive way to store massive amounts of data. Though individual tapes do not reach beyond the 2 terabytes offered by hard drive storage, they are significantly less expensive, more durable and often support spanning data across multiple tapes for extremely large files. Tapes still offer the most failure-resistant long-term backup solution available, particularly for large quantities of data.
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