Advances in Data Storage Technology

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Advances in Data Storage Technology

I. Introduction3
II. Purpose of storage4
III. Hierarchy of storage6
A. Primary storage6
B. Secondary storage7
C. Tertiary storage7
D. Off-line storage8
IV. Characteristics of storage9
A. Volatility9
B. Mutability9
C. Accessibility10
D. Addressability10
E. Capacity11
F. Performance11
G. Energy use11
V. Fundamental storage technologies12
A. Semiconductor12
B. Magnetic12
C. Optical13
D. Paper14
E. Uncommon14
VI. Related technologies17
A. Network connectivity17
B. Robotic storage17


Computer data storage, often called storage or memory, refers to computer components and recording media that retain digital data used for computing for some interval of time. Computer data storage provides one of the core functions of the modern computer, that of information retention. It is one of the fundamental components of all modern computers, and coupled with a central processing unit (CPU, a processor), implements the basic computer model used since the 1940s. In contemporary usage, memory usually refers to a form of semiconductor storage known as random-access memory (RAM) and sometimes other forms of fast but temporary storage. Similarly, storage today more commonly refers to mass storage — optical discs, forms of magnetic storage like hard disk drives, and other types slower than RAM, but of a more permanent nature. Historically, memory and storage were respectively called main memory and secondary storage (or auxiliary storage). Auxiliary storage (or auxiliary memory units) was also used to represent memory which was not directly accessible by the CPU (secondary or tertiary storage). The terms internal memory and external memory are also used.

II. Purpose of storage

Many different forms of storage, based on various natural phenomena, have been invented. So far, no practical universal storage medium exists, and all forms of storage have some drawbacks. Therefore a computer system usually contains several kinds of storage, each with an individual purpose. A digital computer represents data using the binary numeral system. Text, numbers, pictures, audio, and nearly any other form of information can be converted into a string of bits, or binary digits, each of which has a value of 1 or 0. The most common unit of storage is the byte, equal to 8 bits. A piece of information can be handled by any computer whose storage space is large enough to accommodate the binary representation of the piece of information, or simply data. For example, using eight million bits, or about one megabyte, a typical computer could store a short novel. Traditionally the most important part of every computer is the central processing unit (CPU, or simply a processor), because it actually operates on data, performs any calculations, and controls all the other components. Without a significant amount of memory, a computer would merely be able to perform fixed operations and immediately output the result. It would have to be reconfigured to change its behavior. This is acceptable for devices such as desk calculators or simple digital signal processors. Von Neumann machines differ in that they have a memory in which they store their operating instructions and data. Such computers are more versatile in that they do not need to have their hardware reconfigured for each new program, but can simply be reprogrammed with new in-memory instructions; they also tend to be simpler to design, in that a relatively simple processor may keep state between successive computations to build up complex procedural results. Most modern computers are von Neumann machines....
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