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Storage Devices

Lecture # 5

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Storage Devices

Storage devices hold data, even when the computer is turned off.

The physical material that actually holds data is called a storage medium. The surface of a floppy disk is a storage medium.

The hardware that writes data to or reads data from a storage medium is called a storage device. A floppy disk drive is a storage device.

The two primary storage technologies are magnetic and optical.

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Magnetic Storage Devices

Surface of magnetic Disks and tapes are coated with millions of tiny iron particles so that data can be stored on them

Read/Write heads of a magnetic disk or tape drive contains electromagnets that generate magnetic fields in the iron on the storage medium as the head passes over the disk

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A storage device is the computer hardware that records and/or retrieves items to and from storage media Reading is the process of

transferring items from a storage medium into memory

Writing is the process of transferring items from memory to a storage medium

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Access time measures: The amount of time it

takes a storage device to locate an item on a storage medium

The time required to deliver an item from memory to the processor

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Formatting

Formatting is the process of dividing the disk into tracks and sectors so that the operating system can store and locate data and information on the disk

Before a magnetic disk can be used, it must be formatted—a process that maps the disk's surface and determines how data will be stored.

During formatting, the drive creates circular tracks around the disk's surface, then divides each track into sectors.

The OS organizes sectors into groups, called clusters, then tracks each file's location according to the clusters it occupies.

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Areas on Disk

Boot sector File allocation Table (FAT) Root folder Data Area

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How Data is organized on Magnetic Disk

Tracks- circular areas of the disk Length of a track one circumference of

disk Over 1000 on a hard disk Data first written to outer most track

Sectors- Divides tracks sections On a floppy 9 sectors exits

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Cont.

Cylinders- Logical groupings of the the same track on

each disk surface in a disk unit Clusters-

Groups of sectors used by operating system

64 sectors in one cluster Partitioning: divide hard disk into separate

areas called partitions; each partition functions as if it were a separate hard disk drive.

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File Systems

File Allocation Table(FAT) FAT32 New Technology file system (NTFS) NTFS 5 High performance File System (HPFS)

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Floppy Disk

Uses magnetic storage technology Has read / write heads Includes a motor that rotates the disk on a

spindle and read/ write head that can move to any spot on the disk’s surface as the disk spins

Disk Density- the amount of data that a disk can hold

To determine disk density multiply its total number of sectors by the number of bytes each sector can hold

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Hard Disk

Hard disks can store data using longitudinal recording or perpendicular recording

Includes one or more platters mounted on a central spindle

Each platter is covered with a magnetic coating

It includes motor to spin platters and read/write heads

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Other hard Disks

An external hard disk is a separate free-standing hard disk that connects to your computer with a cable or wirelessly

A removable hard disk is a hard disk that you insert and remove from a drive

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Tape

Tape is a magnetically coated ribbon of plastic capable of storing large amounts of data and information

A tape drive reads and writes data and information on a tape

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Optical Disc

An optical disc consists of a flat, round, portable disc made of metal, plastic, and lacquer that is written and read by a laser

An optical disk is a high-capacity storage medium. An optical drive uses reflected light to read data.

To store data, the disk's metal surface is covered with tiny dents (pits) and flat spots (lands), which cause light to be reflected differently.

When an optical drive shines light into a pit, the light cannot be reflected back. This represents a bit value of 0 (off). A land reflects light back to its source, representing a bit value of 1 (on).

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A magnetic stripe card contains a magnetic stripe that stores information

A smart card stores data on a thin microprocessor embedded in the card

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Recordable Optical technologies A CD-Recordable (CD-R) drive lets you record your

own CDs, but data cannot be overwritten once it is recorded to the disk.

A CD-Rewritable (CD-RW) drive lets you record a CD, then write new data over the already recorded data.

PhotoCD technology is used to store digital photographs.

DVD recordable

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Solid state Storage devices

Flash memory Smart Cards

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Solid state Disk