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Article #1: Computer storage overview

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Computer storage, computer memory, and time.)
often casually memory refer to computer Secondary and off-line storage
components, devices and recording media Secondary storage requires the computer
that retain data for some interval of to use its input/output channels to
time. Computer storage provides one of access the information, and is used for
the core functions of the modern long-term storage of persistent
computer, that of information retention. information. However most computer
It is one of the fundamental components operating systems also use secondary
of all modern computers, and coupled with storage devices as virtual memory - to
a central processing unit (CPU), artificially increase the apparent amount
implements the basic Von Neumann computer of main memory in the computer. Secondary
model used since the 1940s. storage is also known as "mass storage",
In contemporary usage, memory usually as shown in the diagram above. Secondary
refers to a form of solid state storage or mass storage is typically of much
known as random access memory (RAM) and greater capacity than primary storage
sometimes other forms of fast but (main memory), but it is also much
temporary storage. Similarly, storage slower. In modern computers, hard disks
more commonly refers to mass storage - are usually used for mass storage. The
optical discs, forms of magnetic storage time taken to access a given byte of
like hard disks, and other types of information stored on a hard disk is
storage which are slower than RAM, but of typically a few thousandths of a second,
a more permanent nature. These or milliseconds. By contrast, the time
contemporary distinctions are helpful, taken to access a given byte of
because they are also fundamental to the information stored in random access
architecture of computers in general. As memory is measured in thousand-millionths
well, they reflect an important and of a second, or nanoseconds. This
significant technical difference between illustrates the very significant speed
memory and mass storage devices, which difference which distinguishes
has been blurred by the historical usage solid-state memory from rotating magnetic
of the terms "main storage" (and storage devices: hard disks are typically
sometimes "primary storage") for random about a million times slower than memory.
access memory, and "secondary storage" Rotating optical storage devices, such as
for mass storage devices. This is CD and DVD drives, are typically even
explained in the following sections, in slower than hard disks, although their
which the traditional "storage" terms are access speeds are likely to improve with
used as sub-headings for convenience. advances in technology. Therefore, the
The fundamental components of a use of virtual memory, which is millions
general-purpose computer are arithmetic of times slower than "real" memory,
and logic unit, control circuitry, significantly degrades the performance of
storage space, and input/output devices. any computer. Virtual memory is
If storage was removed, the device we had implemented by many operating systems
would be a simple digital signal using terms like swap file or "cache
processing device (e.g. calculator, media file". The main historical advantage of
player) instead of a computer. The virtual memory was that it was much less
ability to store instructions that form a expensive than real memory. That
computer program, and the information advantage is less relevant today, yet
that the instructions manipulate is what surprisingly most operating systems
makes stored program architecture continue to implement it, despite the
computers versatile. significant performance penalties.
A digital computer represents information Off-line storage is a system where the
using the binary numeral system. Text, storage medium can be easily removed from
numbers, pictures, audio, and nearly any the storage device. Off-line storage is
other form of information can be used for data transfer and archival
converted into a string of bits, or purposes. In modern computers, CDs, DVDs,
binary digits, each of which has a value memory cards, flash memory devices
of 1 or 0. The most common unit of including "USB drives", floppy disks, Zip
storage is the byte, equal to 8 bits. A disks and magnetic tapes are commonly
piece of information can be manipulated used for off-line mass storage purposes.
by any computer whose storage space is "Hot-pluggable" USB hard disks are also
large enough to accommodate the available. Off-line storage devices used
corresponding data, or the binary in the past include punched cards,
representation of the piece of microforms, and removable Winchester disk
information. For example, a computer with drums.
a storage space of eight million bits, or Tertiary and database storage
one megabyte, could be used to edit a Tertiary storage is a system where a
small novel. robotic arm will "mount" (connect) or
Various forms of storage, based on "dismount" off-line mass storage media
various natural phenomena, have been (see the next item) according to the
invented. So far, no practical universal computer operating system's demands.
storage medium exists, and all forms of Tertiary storage is used in the realms of
storage have some drawbacks. Therefore a enterprise storage and scientific
computer system usually contains several computing on large computer systems and
kinds of storage, each with an individual business computer networks, and is
purpose, as shown in the diagram. something a typical personal computer
Primary storage user never sees firsthand.
Primary storage is directly connected to Database storage is a system where
the central processing unit of the information in computers is stored in
computer. It must be present for the CPU large databases, data banks, data
to function correctly, just as in a warehouses, or data vaults. It involves
biological analogy the lungs must be packing and storing large amounts of
present (for oxygen storage) for the storage devices throughout a series of
heart to function (to pump and oxygenate shelves in a room, usually an office, all
the blood). As shown in the diagram, linked together. The information in
primary storage typically consists of database storage systems can be accessed
three kinds of storage: by a supercomputer, mainframe computer,
Processor registers are internal to the or personal computer. Databases, data
central processing unit. Registers banks, and data warehouses, etc, can only
contain information that the arithmetic be accessed by authorized users.
and logic unit needs to carry out the Network storage
current instruction. They are technically Network storage is any type of computer
the fastest of all forms of computer storage that involves accessing
storage, being switching transistors information over a computer network.
integrated on the CPU's silicon chip, and Network storage arguably allows to
functioning as electronic "flip-flops". centralize the information management in
Cache memory is a special type of an organization, and to reduce the
internal memory used by many central duplication of information. Network
processing units to increase their storage includes:
performance or "throughput". Some of the Network-attached storage is secondary or
information in the main memory is tertiary storage attached to a computer
duplicated in the cache memory, which is which another computer can access at file
slightly slower but of much greater level over a local-area network, a
capacity than the processor registers, private wide-area network, or in the case
and faster but much smaller than main of online file storage, over the
memory. Multi-level cache memory is also Internet.
commonly used—"primary cache" being Storage area network provides other
smallest, fastest and closest to the computers with storage capacity over a
processing device; "secondary cache" network, the crucial difference between
being larger and slower, but still faster network-attached storage (NAS) and
and much smaller than main memory. storage area Networks (SAN) is the former
Main memory contains the programs that presents and manages file systems to
are currently being run and the data the client computers, whilst a SAN provides
programs are operating on. In modern access to disks at block addressing
computers, the main memory is the level, leaving it to attaching systems to
electronic solid-state random access manage data or file systems within the
memory. It is directly connected to the provided capacity.
CPU via a "memory bus" (shown in the Network computers are computers that do
diagram) and a "data bus". The arithmetic not contain internal secondary storage
and logic unit can very quickly transfer devices. Instead, documents and other
information between a processor register data are stored on a network-attached
and locations in main storage, also known storage.
as a "memory addresses". The memory bus Confusingly, these terms are sometimes
is also called an address bus or front used differently. Primary storage can be
side bus and both busses are high-speed used to refer to local random-access disk
digital "superhighways". Access methods storage, which should properly be called
and speed are two of the fundamental secondary storage. If this type of
technical differences between memory and storage is called primary storage, then
mass storage devices. (Note that all the term secondary storage would refer to
memory sizes and storage capacities shown offline, sequential-access storage like
in the diagram will inevitably be tape media.
exceeded with advances in technology over






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