medium (pi. media) ; capacity ; ();
media capacity
data access time
per bit
to transfer (); (); -()
archival storage ; to depend ; , to rotate (); (); () reason ; ; ; ;
solid-state device magnetic core
. 90
bipolar semiconductor
metal-oxide semiconductor (MOS) -- randomly
random-access memory (RAM) ()
sound recording
to arrange ; ; ;
tape device
to range ; ;
magnetic disc storage
moving-head device
predominant ; flexible ; ; floppy (disk) (); to meet the demands
9. 2 , . .
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
91 Unit 7. Storage
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. Magnetic 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 processing. They are classified as moving-head, fixed-head, or combination 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 medium to meet the demands of the microcomputer market.
|
. 92
10. , .
1. How are storage media classified? 2. How is the cost of storage devices expressed? 3. What is the access time for storage media? 4. How does the storage capacity range? 5. What are the two main types of storage devices? 6. What are electronic storage devices? 7. What are the principal primary storage circuit elements? 8. What are the main secondary storage devices? 9. What is the oldest secondary medium and when was it invented? 10. What is a floppy?
11.
:
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;. ; ; ; ; ; ; .
.
93__________________________________ Unit 7. Storage
13. ,
: Participle I, Participle II, Perfect
Participle Active Perfect Participle Passive.
1. Electromechanical memories depend upon moving mechanical parts for their operation. 2. The time required for the computer to locate and transfer data to and from a storage medium is called the access time. 3. Being not visible software makes possible the effective operation of computer system. 4. Having invented magnetic tapes the Germans used them as the secondary storage medium. 5. When properly programmed computers don't make computational errors. 6. Having been introduced in the early 1960s magnetic disc storage has replaced magnetic tape storage. 7. The control unit interpreting instructions is one of the important parts of any computer system. 8. Data recorded in the form of magnetized dots can be arranged to represent coded patterns of bits. 9. As contrasted with magnetic tapes magnetic discs can perform both sequential and random processing. 10. While having no moving mechanical parts electronic memories can transfer data at very high speed.
|
|
|
.
