Text 2. STORAGE DEVICESStorage medi

Text 2. STORAGE DEVICES
Storage media are classified as primary storage or secondary storage on the basis of combinations*of cost, capacity, and access time. The cost of storage devices is expressed as the cost per bit of data stored. The most common units of cost are cents, millicents (0.001 cents) and microcents (0.000001 cents). The time required for the computer to locate and transfer data to and from a storage medium is called the access time for that medium. Capacities range from a few hundred bytes of primary storage for very small computers to many billions of bytes of archival storage for very large computer systems.
Memories may be classified as electronic or electromechanical. Electronic memories have no moving mechanical parts, and data can be transferred into and out of them at very high speeds. Electromechanical memories depend upon moving mechanical parts for their operation, such as mechanisms for rotating magnetic tapes and disks. Their data access time is longer than is that of electronic memories; however they cost less per bit stored and have larger capacities for data storage. For these reasons most computer systems use electronic memory for primary storage and electromechanical memory for secondary storage.
Primary storage has the least capacity and is the most expensive; however, it has the fastest access time. The principal primary storage circuit elements are solid-state devices: magnetic cores and semiconductors. For many years magnetic cores were the principal elements used in digital computers for primary storage. The two principal types of semiconductors used for memory are bipolar and metal-oxide semiconductors (MOS). The former is faster, the latter is more commonly used at present. Because data can be accessed randomly, semiconductor memories are referred to as random-access memory, or RAM.
There is a wide range of secondary storage devices. Typical hardware devices are rotating electromechanical devices. Mag¬netic tapes, disks, and drums are the secondary storage hardware most often used in computer systems for sequential processing. Magnetic tape, which was invented by the Germans during World War II for sound recording, is the oldest secondary storage medium in common use. Data are recorded in the form of small magnetized "dots" that can be arranged to represent coded patterns of bits.
Tape devices range from large-capacity, high-data-rate units used with large data processing systems to cassettes and cartridges used with small systems. Magnetic disk storage, introduced in the early 1960s, has replaced magnetic tape as the main method of secondary storage. As contrasted with magnetic tapes, magnetic discs can perform both sequential and random pro¬cessing. They are classified as moving-head, fixed-head, or com¬bination moving-head and fixed-head devices. Magnetic discs are the predominant secondary storage media. They include flexible, or floppy discs, called diskettes. The "floppies" were introduced by IBM in 1972 and are still a popular storage me¬dium to meet the demands of the microcomputer market.

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Text 2. STORAGE DEVICESStorage media are classified as primary storage or secondary storage on the basis of combinations*of cost, capacity, and access time. The cost of storage devices is expressed as the cost per bit of data stored. The most common units of cost are cents, millicents (0.001 cents) and microcents (0.000001 cents). The time required for the computer to locate and transfer data to and from a storage medium is called the access time for that medium. Capacities range from a few hundred bytes of primary storage for very small computers to many billions of bytes of archival storage for very large computer systems.Memories may be classified as electronic or electromechanical. Electronic memories have no moving mechanical parts, and data can be transferred into and out of them at very high speeds. Electromechanical memories depend upon moving mechanical parts for their operation, such as mechanisms for rotating magnetic tapes and disks. Their data access time is longer than is that of electronic memories; however they cost less per bit stored and have larger capacities for data storage. For these reasons most computer systems use electronic memory for primary storage and electromechanical memory for secondary storage.Основное хранилище имеет наименьшее потенциала и является самым дорогим; Однако он имеет самое быстрое время доступа. Основной первичный хранения цепи элементы твердотельных устройств: магнитных сердечниках и полупроводников. На протяжении многих лет магнитных сердечниках были основные элементы, используемые в цифровых компьютерах для первичного хранения. Два основных типа полупроводников, используемых для памяти являются биполярного и металло оксидных полупроводников (MOS). Первый быстрее, более широко используется в настоящее время. Потому, что данные могут быть доступны случайно, полупроводниковые воспоминания упоминаются как память или ОЗУ.Существует широкий спектр устройств вторичного хранения. Типичные аппаратные устройства вращение электромеханических устройств. MAG¬netic ленты, диски и барабаны являются вторичного хранения оборудования, наиболее часто используется в компьютерных системах для последовательной обработки. Магнитная лента, которая была изобретена немцами во время второй мировой войны для записи звука, является старейшим вторичный носитель в общего пользования. Данные записываются в виде небольших Намагниченный «точек», могут быть организованы для представления закодированных шаблоны битов.Ленточные устройства в диапазоне от большой емкости, высокой данных скорость единицы, используемые с большими обработки данных систем для кассет и картриджи с малых систем. Магнитный диск хранения, представил в начале 1960-х, заменил магнитной ленты в качестве основного метода вторичного хранения. Как контрастирует с магнитной ленты, магнитные диски может выполнять как последовательный, так и случайных pro¬cessing. Они классифицируются как перемещение головы, купе или com¬bination устройства перемещения головы и купе. Магнитные диски являются преобладающим вторичного хранения средств массовой информации. Они включают в себя гибкие, или гибких дисков, называется дискеты. «Дискет» были введены компанией IBM в 1972 году и по-прежнему являются популярными хранения me¬dium для удовлетворения потребностей рынка микрокомпьютера.