Secondary storage devices include external storage mediums like USB drives, external hard disks, and zip drives that are used to backup and store files externally from the main computer. Peripheral devices expand the capabilities of the host computer but are not part of the core architecture, and include input, output, and storage devices. The control unit decodes instructions and controls data flow and timing in the central processing unit. It regulates communication between the CPU and peripheral devices. The arithmetic logic unit performs arithmetic and logical operations and works with the control unit to execute instructions.

1. - Simant Shrestha
- As – level
- 013A056
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2. Secondary Storage
 The storage which are used as backup or the place
where we save the files for our use is known as
secondary storage.
 E.g. Pen-drive , external hard-disk , Zip-drive e.t.c
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3. Peripheral Devices
 A peripheral is a device that is connected to a host
computer, but not part of it. It expands the host's
capabilities but does not form part of the core computer
architecture. It is often, but not always, partially or
completely dependent on the host.
 E.g. Input Devices, Output Devices, Storage Devices.
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4. Control Unit
 It also takes help from the arithmetic logic unit , whenever required.
 Functions of Control Unit:
A control unit can be described as a sort of circuitry that supervises and
controls the path of information that runs over the processor and organizes the
various activities of those units that lie inside it.
• It carries out many tasks such as decoding, fetching, handling the execution
and finally storing the results.
• It controls the execution of instructions in a sequential order.
• It guides the flow of data through the different parts of the computer.
• It interprets the instructions.
• It regulates the time controls of the processor.
• It sends and receives control signals from various peripheral devices.
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5. Arithmetic logic Unit (ALU)
 An arithmetic logic unit is the part of a computer’s central processing unit (CPU) that
allows the computer to make numerical calculations and logical decisions.
 ALU - Arithmetic Logic Unit, takes inputs from (usually 2) buses, performs a selectable
operation, and returns an output (usually 1) onto a bus. has no memory.
 The ALU is the main component of the CPU (central processing unit).
 In a way, the ALU is where you have at least one argument: the last answer, and can make
an operation to this: A + B -> C.
The operation "+" can be arithmetic, like addition or it is logical like AND or to compare
two numbers.
 It performs arithmetic operation like
addition, subtraction, increasement, multiplication.
 It performs logical operation like AND -ing, OR-ing, X-OR-ing, NOT
etc.
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6. USB Drives
Floppy Disks
CD-R
DVD-R
Magnetic Tape
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7. USB Drives
 A USB flash drive, usually portable and
rewritable, is a type of flash memory storage
device that plugs into a computer's USB port. Flash
drives are more expensive than hard drives with
the same storage capacity.
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8. Floppy Disks
 Floppy disks are a storage medium made of a thin
magnetic disk. They were widely used from the
1970s to the early 2000s. On the 3 1⁄2-inch
microfloppy, common from the late 1980s
onward, storage capabilities ranged from the
standard 1.44 MB to 200 MB on some versions.
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9. CD-R
 A CD-R, a type of recordable CD, is an optical secondary
storage device invented by Sony and Philips. It is also
known as a WORM -- write once read many -- medium.
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10. DVD-R
 A DVD-R, a type of recordable DVD, has a storage
capacity of usually 4.1 GB. There is also an 8.54-GB
dual-layer version, called DVD-R DL.
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11. Magnetic Tape
 Magnetic tape has been in use for more than 50 years.
Modern magnetic tape is packaged in cartridges or
cassettes and is used for storing data backups, particularly
in corporate settings. The average amount of storage is 5
MB to 140 MB for every standard-length reel, which is
2,400 feet.
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12. Advantages of Secondary Storage
Device
 Secondary storage devise are non -volatile memory ..that is they are permanent storage
devices..
-Prevent lost of data..
-backups
 A Tape Streamer is used for making backups of files held on computer systems.
 A floppy disk has the advantage that it can be written onto and taken away from the
 A hard drive has the advantages of being fast to access and also stores massive amounts
of data computer. Because of this it can be used for storing confidential files.
 A CDROM cannot be altered. This disadvantage can be turned into an advantage if the
owner does not want the contents of the storage to be altered. Examples of files stored on
CDROM are software for import to a system and large reference files like encyclopedias.
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13. Disadvantages of Secondary
Storage Device
 Hard Disk Drive Consumes allot of power, the resistance of shocks is low, data error
rates are frequent, weight ratios are large, the size is large, can be hard to recover data
from, (SCSI) controller cards may be required, loud mechanical noise can be
generated, heat can be generated, there are moving parts inside, the disk sectors will
eventually stop working, and they can be broken if dropped (usually whilst operating).
 Solid State Drive the price of SSD is still high. Per gigabyte of SSD, it costs US $1.50 ~ US
$3.45.
 Optical Drive affordability endless media expenses each but are considerably less
reliable with each recording and are not recommended for long-term or archival use.
 Flash Drive/Storage Card these cards offer a lot of convenience, they also have their
drawbacks. Flash memory cards are small.
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14. Use of Secondary Storage Media
 The means by which the data are stored:
 Optically,
 Magnetically or
 On a solid state.
 Magnetic Tape
 It is Particularly used for long-term storage of archive material and for backup copies of large files.
 Characteristics of Magnetic Tapes
 No direct access, but very fast sequential access.
 Resistant to different environmental conditions.
 Easy to transport, store, cheaper than disk.
 Before, it was widely used to store application data; nowadays,
 it's mostly used for backups or archives (tertiary storage).
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15.  - Optical Storage:
 Similar to Magnetic storage, but the data is stored as light and read by lasers The CD surface is a mirror
covered with billions of tiny bumps that are arranged in a long, tightly wound spiral.
 The CD player reads the bumps with a precise laser and interprets the information as bits of data.
 The spiral of bumps on a CD starts in the center. CD tracks are so small that they have to be measured
in microns (millionths of a meter).
 The CD track is approximately 0.5 microns wide, with 1.6 microns separating one track from the next.
 The elongated bumps are each 0.5 microns wide, a minimum of 0.83 microns long and
125 nanometers (billionths of a meter) high.
 The optical storage device that most of us are familiar with is the compact disc(CD).
 A CD can store huge amounts of digital information (783 MB) on a very small surface that is incredibly
inexpensive to manufacture. The design that makes this possible is a simple one:
 Most of the mass of a CD is an injection-molded piece of clear polycarbonate plastic that is about 1.2
millimeters thick.
 During manufacturing, this plastic is impressed with the microscopic bumps that make up the
long, spiral track. A thin, reflective aluminum layer is then coated on the top of the disc, covering the
bumps.
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16.  The tricky part of CD technology is reading all the tiny bumps correctly, in the right
order and at the right speed. The CD player has to be exceptionally precise when it
focuses the laser on the track of bumps.
 When you play a CD, the laser beam passes through the CD's polycarbonate layer, reflects
off the aluminum layer and hits an optoelectronic device that detects changes in light.
 The bumps reflect light differently than the flat parts of the aluminum layer, which are
called lands.
 The optoelectronic sensor detects these changes in reflectivity, and the electronics in the
CD-player drive interpret the changes as data bits.
 Solid-state storage is a nonvolatile, removable storage medium that employs ICs or
integrated circuits (all confined entirely within the solid materi.al) rather than magnetic or
optical media.
 It is the equivalent of large-capacity, nonvolatile memory.
 The main advantage of solid-state storage is the fact that it contains no mechanical parts.
Everything is done electronically.
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17. CR-ROM Magnetic Disks
CLV = Constant Linear Velocity CAV = Constant Angular Velocity
Sectors organized along a spiral Sectors organized in concentric track
Sectors have same linear length (data packed
at its maximum density
Permitted
Sectors have same angular length (data
written less densely in the outer tracks)
Advantage: takes advantage of all storage
space available
Advantage: operates on constant speed,
timing marks to delimit tracks
Disadvantage: has to change rotational
speed when seeking (slower towards the
outside)
Disadvantage: it doesn't use up all storage
Available
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18. THANK YOU
ANY
QUESTIONS
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