Hardware(AS level)

- Simant Shrestha

- As – level

- 013A056

Simant Shrestha -_- 1

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


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.


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.

4Simant Shrestha -_-

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.


USB Drives

Floppy Disks

CD-R

DVD-R

Magnetic Tape


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.


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.


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.


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.


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.


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.


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.


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).


- 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.


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.


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 packedat its maximum densityPermitted

Sectors have same angular length (datawritten less densely in the outer tracks)

Advantage: takes advantage of all storagespace 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 storageAvailable


THANK YOUANY QUESTIONS


Technology

Hardware(AS level)