storage device

Document Sample
storage device Powered By Docstoc
					MAIN CATEGORIES: STORAGE DEVICES
Magnetic storage device – backing storage:
A magnetic storage device is a device that uses a
magnetic head to read and write data to and from a
magnetizable medium. The medium is usually plastic tape
that is coated with fine particles of a metal, such as tape
storage devices.


Some examples are:
    Fixed discs (internal) – a hard magnetic disk mounted in a drive unit.
    Portable discs
    VHS
    Floppy discs
    Magnetic tape



Floppy Disks

One of the most popular types of magnetic
storage was floppy disks, which aren’t used as
much today since we are advancing in many ways.
Floppy disks were advantageous at the time due to
their low cost and ease to make. They recorded
data using a magnetic head and rotating media.
Floppy disks had drawbacks such as a low storage capacity—which allowed only 1.44 megabytes of
information to be stored. They also had low data transfer rates, meaning that they took a long time to
transfer data between sources.

Magnetic Tape

Magnetic tape was advantageous when it was introduced because it was very small and thin. It could
also be wound upon itself; it utilized a limited amount of space. Just like other magnetic tape
technologies, it had several disadvantages as well. These include durability; if any area of the tape is
damaged or broken, it can lead to the entire role being useless. There is also only a small amount of
space to record data on magnetic tape.

Hard Disk Drives
                                  Hard disk drives are commonly found
                                  within computers. They were first
                                  introduced in 1957, being extremely
                                  impractical and disadvantageous at the
                                  time because of their large 24-inch
                                  diameter. They originally could hold 5
                                  Megabytes of information.
                                   But hard drives have improved and have
grown into a more than $30 billion dollar per year industry with the
widespread use of computers across the globe. They offer high-speed accessibility and are cheap to
make. Occasionally hard disk drives are prone to error; however, advances in technology have made
them more reliable.



In my opinion from looking and comparing from the three I think hard drives are more useful and
reliable because of their space capacity, although the cost is



                                                                                                 Variation of
                               360 KB       1.2 MB        720 KB        1.44 MB      2.88 MB     magnetic
Category     Specification
                                5.25"        5.25"         3.5"           3.5"         3.5"      tape
             Read/Write
             Heads (Data         2             2             2             2            2
  Drive       Surfaces)

             Spindle Motor
                              300 RPM      360 RPM       300 RPM       300 RPM       300 RPM
                 Speed

              Minimum
Controller    Controller     250 Kbits/s   500 Kbits/s   250 Kbits/s   500 Kbits/s   1 Mbits/s
             Transfer Rate




Optical storage- backing storage:
Optical storage is any type of storage method where data is
written and read with a laser. Usually, data is written to optical
media, like CDs and DVDs. Computer scientists have said how
optical storage is a near-future replacement for both hard
drives in personal computers and tape backup in mass storage.

Optical media is more durable than tape and less vulnerable to
environmental conditions. Although, it tends to be slower than
typical hard drive speeds, and offers slower storage capacities.
Current optical speeds are approaching those of hard drives. A
number of new optical formats like Blu-ray and, use a blue laser
to dramatically increase capacities.

How they work:

An optical storage drive that is capable of writing data to a disc uses a laser beam to punch tiny holes
into a special material. The data stream is then placed in a spiral path; the data begins at the center and
works its way out toward the edge of the disc. In industrial mass produced discs, such as those
distributing music or movies, the data is placed on the disc by a stamping machine. Data is retrieved by a
laser beam that reflects off the disc, detecting the
holes. Optical drives come in different speeds,
spinning between 200 and 4,000 RPMs.



Some example of optical storages can be: CD-R, CD-
RW, DVD-R, DVD-RW, Blu-ray

       CD-R (or CD-ROM) is a read-only-memory
        optical disc which can be written to only once.
       CD-RW (or "re-writable") can be written to many times, similar to a VHS videotape.
       The same designation is used for read-only DVDs (DVD-R or DVD-ROM) and re-writable DVDs
        (DVD-RW).
       Blu-ray discs, can store more information in the same physical space. These are useful for
        storing such content as High Definition movies.



Storage Capacity:

The standard storage capacity for CDs is about 700MB (megabytes). That's enough space to store over
300,000 pages of text or about 80 minutes of music. A full-length movie can be stored on a DVD, which
holds about 4.7GB (gigabytes) of memory. The data on optical discs is estimated to be viable for five to
10 years, so discs storing valuable data should be checked occasionally, and fresh copies made after
several years. Store them upright in cases, and keep them in a dry, room temperature environment.

The bad thing is that unlike hard disks, which are in a sealed unit, and floppy disks, which are in a
protective housing; optical discs have no protection once they are removed from their storage case.
Optical discs are vulnerable to scratches, dirt, breakage and fingerprints, although fingerprints can
usually be removed by wiping with a soft, damp cloth.




Solid State backing storage devices:

Flash Disks
• They are external to the computer and also portable
• Flash disks capacity are getting bigger and bigger as time goes by, they used to be 32MB but now you
can get really big ones, like 256GB
• They can transfer data at 11MB per second
• For the size ratio of flash disks to floppy disks, flash disks are much cheaper. If you want a 16GB flash
disk in floppy disks, you would need over 16,000, and each floppy disk costs about 1$
• The cheapest flash disk I could find is $2.88 for 4GB. That is 72 cents per gigabyte, and $0.0007 per
megabyte
• Random access – which means that you can pick any of the information from it, no matter what order
it is already in



Memory Cards
• They are left inside cameras, but can be taken out, and they are also portable
• Now you can get SD cards which are as big as 16GB
• The fastest SD card to computer transfer rate I found was 9MB per second
• The cheapest memory card I could find was $6.93. This was for 2GBs. So, that is $3.47 per gigabyte.
And, divided by 1024, which would be $0.003 per megabyte.
• Random access – which means that you can pick any of the information from it, no matter what order
it is already in
Input device categories:

Keyboards -

How does a computer keyboard work?

Computer keyboards are an input device.
They put the information when someone
types into the computer. Most keyboards
have 80 to 110 keys. The numbers and letters
on the keyboard are displayed keycaps--these
are the buttons that are pressed when a person types.
A circuit is cut when a key is pressed; the closing of the circuit signals the processor to read the key map
inside it, then using the key map the processor in the keyboard can tell which letter is being pushed.


What are they used for?


A keyboard is where you put input data and command
functions on a computer. The most common use for a keyboard
is making text or numbers appear and disappear on the screen.
The keyboard can also be used to do things like cutting and
pasting data and to close and open windows in some operating
systems.


What are the advantages and disadvantages?
Advantage                                                                     1 . Inside of a keyboard

       The only real advantage the QWERTY keyboard has for computers and laptops is familiarity.
        Because it has existed for so long, it is the first method most people use when learning to type,
        and many are reluctant to learn a new layout later in life
       Also because it is laid out so all the keys are easy to reach.


Disadvantage

       The problem is that know there has been a new layout (drvok) that is more efficient, and
        doesn’t cause carpal tunnel syndrome like the QWERTY layout.
       Drvok has 30% less hand movement

There are different categories on the keyboard such as…

                         Alphanumeric – a set of characters: letters ,numbers and punctuation marks
       Pin pad -




Pointing devices-

A pointing device is any piece of hardware that is used
to allow a user to input spatial data to a computer. By
moving a mouse, pen or a finger around, a user can
make movements and changes on the computer screen.

What are they used for?

A pointing device is an external tool that is used to
move objects around and also to select options from menus

How do they work?

                                   The mouse gives the computer user the freedom to move cursors in
                                   any direction, unlike the arrows on a keyboard, which constrain the
                                   user to a limited set of directions because its really hard to move it
                                   around the screen. Also the mouse can be fine-tuned to each user, so
                                   that movements can match with the user's expectation. For example,
                                   you can adjust the speed of the cursor so that it will travel a farther
                                   or shorter distance with the mouse movement. Computer mice are
                                   also popular input devices for many computer games since they are
                                   highly responsive and accurate for user input.

                                   Computer mice need an unobstructed and flat surface to effectively
monitor and manage user movements. However, flat surfaces may not always be available, especially as
computer users become more mobile with laptop computers, and this may cause limited use of the
mouse. In addition, even wireless mice require the computer user to be relatively close to the computer
to register mouse movements.

The computer mouse is one of the most common input devices on computers. However, there are many
variations to the standard computer mouse. Computer mice can have a single button or many buttons
along with a scroll wheel. Wireless mice are available. Mice also may have trackballs or use optical light
to sense movement. However, while computer mice are because of several advantages, there are still a
few disadvantages to computer mice as well.
There are a large variety of computer mice to suit individual needs. Small compact mice are available for
frequent travelers or mobile computer users. Optical mice are available to avoid previous problems with
trackball-based mice, when they became dirty or obstructed. Mice can have a single button or many
buttons to support control and minimize the need to switch often between a keyboard and the mouse



Types of Pointing Devices:

    1. Track ball

A trackball mouse is stationary, with a moveable ball. Users control the
cursor on the screen by scrolling the ball, instead of moving their entire
hand. While this is convenient, it has its disadvantages also.

What are the advantages and disadvantages?

Advantages

The trackball mouse is helpful because it allows people to move the cursor without having to move the
entire mouse. This reduces strain on the user's wrist, hands, arms, and shoulders. Trackball users can
also operate the buttons more easily without accidentally moving the mouse itself. Trackball mice also
use less space than a traditional mouse, and do not require a mouse pad.

Disadvantages

       The problem with track balls is that sometimes the movements are not completely precise. For
        designers and those who work in graphics, the customary mouse may have greater accuracy.
        Another disadvantage is that the ball mechanism requires more cleaning and maintenance than
        a regular mouse.
       Also trackballs are generally more expensive than regular mice. The average price of a trackball
        mouse is $39.99. Customers can purchase an inexpensive Logitech TrackMan Marble Mouse for
        $24.99.
       It also causes pain in the wrist which is also called carpel tunnel syndrome



    2. Touch screen:



The touch pad which can be found on laptops, this detects the movement of a finger and moves the
arrow accordingly. By tapping on the pad, the user is able to create a click. This has made it much
simpler to use a laptop computer than it used to be.

What are the advantages & disadvantages?
3. Graphics tablet



 A graphics tablet is a computer input device that allows you to
 draw images and graphics, so it would be like you draw with a
 pencil and paper. These tablets may also be used to capture
 data or handwritten signatures. This is a tablet that, when
 using a pen or "mouse," the person can make the arrow move.
 Instead of being a mouse with a roller ball or optical light, this relies on the actual table to bring the
                               movement. Each point on one of these tablets represents a point on
                               the monitor. So that if you touch the bottom right hand corner, the
                               arrow will move to the bottom right hand corner.



                                 What are the advantages and disadvantages?

                                 Advantage-
                              These tablets come with a pen that you use to draw the image onto
                              the surface of the tablet. A graphics tablet provides the users with
   much greater control over the image. This is because the users can manipulate the digital pen in
   much the same way that they would a regular drawing pen or brush, allowing them to achieve a
   smooth motion that the mouse cannot match.
   Another useful feature of graphics tablets is that they are usually pressure sensitive. Many
   graphics programs have been designed to detect this pressure difference and express it on the
   canvas. This means that as the artist applies more pressure the program will apply more "paint,"
   while if he gradually releases the pressure decreases.


   Disadvantage-
   The problem with using graphic tablets is when you try to coordinate the movement of your
   hand with the action on the screen. With a mouse it is generally easier to coordinate your
   movement with the action on the screen. An alternative is to use a graphics tablet that actually
   has its own built in screen. This gives digital graphics artists the same kind of immediate visual
   feedback they would get with a pencil and paper.
        How does it work?


       Graphic tablets can be used in place of a mouse. They use
        the fluid motion and natural positioning of the human hand
        to its best advantage. Using a graphic tablet is as easy and
        as comfortable as using a pen, pencil or airbrush, as the
        case may be, and they are being used in more and more
        industries.
       The tablets capture the image as data which can be stored as a file or document. Graphics
        tablets can be used like a large marker board to take notes on or create outlines.
       Graphics tablets are flat surfaces that are drawn using a pen device. The tablet is attached to the
        computer and the pen to the tablet. The tablet reads the marks made by the pen and puts them
        on the screen.
       The angle or tilt of the pen, the pressure being placed on the pen and the distance from pen to
        tablet are interpreted by the tablet. A hand-held device called a puck has been designed to use
        in place of the pen. The puck looks similar to a mouse but is different in that it knows its
        absolute position on the drawing tablet.




Output devices:


Printers-

Printers are output devices that produce copies of data.



1) Inkjet printers:

Ink jets spray liquid ink onto paper to form letters and images.
Ink jet printers are the most popular printers for home use and
are often the least expensive. Numerous models with decent
image quality are available for less than $100, but the real cost
comes when replacing ink cartridges, sometimes it can cost more
than the printer itself! The cost of ink jet printers ranges from less
than $100 for low-end machines to $500 or more for photo-quality
printers.


How does it work?

    Inkjet printers use electronic impulses to spray tiny drops of ink as the paper passes underneath the
    print head. This process has the advantage of allowing for the easy integration of color, but
    sacrifices speed to allow the ink to dry sufficiently after each pass of the print head.



What are the advantages & disadvantages?

Advantages:

       Inkjet printers typically are smaller than laser jet printers, so they can save you valuable space.
       Inkjet printers are usually quieter than laser printers, which tend to be noisy.

       Inkjet printers are often cheaper than laser printers. If you need a basic printer that can
        accomplish printing tasks at a reasonable level of quality, an inkjet printer is the best choice.

       It also gives high quality printouts

Disadvantage:

       The ink cartridges are expensive
       Sometimes inkjet cartridges get clogged or dirty, which either blocks the ink droplets or causes
        them to land incorrectly. Laser jet printers
        do not have this problem.
       You can't use all types of paper with an
        inkjet. With the wrong type of paper, the
        printed ink may smear
       They don’t print black and white text as fast
        as laser printers.
       Certain types of printouts, like as color
        images, take a long time to dry.
       Also moisture cause printed ink to smudge.
2) Laser printers:


Laser printers are computer printers that print graphics and word documents on paper. They have
higher quality and efficacy than other, like multifunction printers or digital photocopiers.



How does it work?

Laser printers use toner (powdery stuff), the paper is fed into the printer and the drum inside the printer
rotates, along the bottom there is a black sponge roller . it then applies a positive charge on the back
                                                                side of the paper and the negatively
                                                                charged falls on to the back side of the
                                                                paper. Then the paper goes into a device
                                                                called a fuser then it is steam rolled onto
                                                                the paper.

                                                              What are the advantages and
                                                              disadvantages?

                                                              Advantages:

                                                                    Laser printers run quieter and
                                                              faster than most printing machines
                                                                    They require less maintenance
                                                              than cartridge printers
       Some laser printers can produce upwards of 40 pages per minute.
       Laser printers can be as much as six times faster than inkjet printers when printing black text.
       They can last for many years
       Laser printers, on the other hand, are often bulky



Disadvantage:

       Lasers are also not designed to produce photo-quality prints, as the mechanics of toner
        formulation don't lend themselves to quality and durability the same way that inkjet inks do.
        Also, laser printers are not designed to handle photo paper, but if print and paper quality are
        not critical, many newer color laser printers create acceptable photo prints.

       Laser printers can break down easily, even though they can be replaced or repaired.
2) Dot Matrix

Dot matrix printers, also known as impact printers, are capable of printing text and simple graphics. The
printer draws one character at a time from a dot matrix, usually consisting of either 9 or 24 pins, then
striking a number of metal pins against an inked ribbon, transferring the image to a sheet of tractor-feed
paper. A dot matrix printer can print at high speed

How do they work?

A print head sweeps across the surface of the page while tiny pins punch through an ink ribbon, much
like an old-fashioned typewriter. Images and text are assembled line by line and dot by dot, Prices range
from $200 for low-end machines to $700 or more for heavy-duty
high-output printers.



    Advantages & disadvantages:

    Advantages:

       It is easy to use
       As the ink is running out it fades gradually than stopping
        halfway through the job.
       They are able to use continuous papers than individually.
        Maintenance and replacement ink ribbons are usually
        inexpensive.



    Disadvantages:

       They are not as fast as other printers.
       The resolution isn’t as good as normal printers .
       The printers are very noisy
       They are more prone to jamming

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:4
posted:5/19/2012
language:English
pages:12
fanzhongqing fanzhongqing http://
About