Download Secondary Storage - Information Technology

MODULE NAME: Fundamentals Information Technology
TOPIC: Secondary Storage
LECTURE 4
SECONDARY STORAGE
Secondary storage is that type of storage that is mainly concerned with holding data
permanently (for later use).
Secondary storage is also known as:
 Auxiliary Storage
 Backing Storage
Secondary Storage is referred to as “non-volatile” storage. When the power goes the
information stored on the secondary storage device remains.
Types of Secondary Storage Medium
Magnetic Disk
There are two main types of magnetic disk:
 Floppy Disk
 Hard Disk
Floppy Disk – a portable type of storage. The most popular size 3 ½” is used to store up
to 1.44 megabyte of data. Floppies consist of a thin flexible plastic disk that is coated
with a magnetisable substance like oxides of iron or chromium (or a combination of the
two).
Floppy Disk
Hard Disk – These are otherwise called “Fixed disk”. It stores all the information that is
on your computer. The hard disk has a hard platter that holds the magnetic medium, as
opposed to the flexible plastic film found in tapes and floppies.
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Hard Disk
Although both floppies and hard disk use random access or direct access (this moves to
any point on the disk surface almost instantly), the platter in the hard disk rotates
approximately twenty times faster than that of a floppy disk. As a result the hard disk is
considered on of the fastest secondary storage.
Magnetic Tape – This is similar to the continuous reel of recording surface in an audio
videocassette. It is made from magnetisable plastic. You cannot go directly to an item of
data on a tape as you can on a disk. It is necessary to start at the beginning of the tape and
search for the data as the tape goes past the read head. This kind of access is known as
“Serial access” or “Sequential Access”.
Magnetic Tape
Zip Disk – This is a 3.5" removable disk drive from Iomega. Zip disks come in 100MB,
250MB and 750MB varieties, with the latter introduced in 2002 using USB and FireWire
interfaces.
Zip disks are a floppy-like technology that uses design concepts from hard disks.
Zip Disk
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Sector
A sector is the smallest unit that can be accessed on a disk. When a disk undergoes a
low-level format, it is divided into tracks and sectors. The tracks are concentric circles
around the disk and the sectors are segments within each circle. For example, a formatted
disk might have 40 tracks, with each track divided into 10 sectors. The operating system
and disk drive keep tabs on where information is stored on the disk by noting its track
and sector number.
Modern hard disk drives use a technique called zoned-bit recording in which tracks on
the outside of the disk contain more sectors than those on the inside.
A sector that cannot be used due to a physical flaw on the disk is called a bad sector.
Track
A track is a ring on a disk where data can be written. A typical floppy disk has 80
(double-density) or 160 (high-density) tracks. For hard disks, each platter is divided into
tracks, and a single track location that cuts through all platters (and both sides of each
platter) is called a cylinder. Hard disks have many thousands of cylinders.
Each track is further divided into a number of sectors. The operating system and disk
drive remember where information is stored by noting its track and sector numbers.
The density of tracks (how close together they are) is measured in terms of tracks per
inch (TPI).
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Flash Drives – These are small, portable flash memory card that plugs into a computer’s
USB port and functions as a portable hard drive. USB flash drives have less storage
capacity than an external hard drive, but they are smaller and more durable because they
do not contain any internal moving parts.
USB flash drives also are called thumb drives, jump drives, pen drives, key drives, tokens,
or simply USB drives.
Optical Disk Storage
This technology uses laser light to read or write (burn) data onto an optical medium.
Optical disks use random access.
Different Varieties of CDs exists such as CD-R, CD RW, CD ROM etc and can store
over 700 MB of data.
Compact Disk Read Only Memory (CD-ROM) – The CD drive reads data with a beam
of light so narrow that the information can be squeeze together very tightly. As a result,
the CD storage capacity is large.
CD
Compact Disk Recordable (CD-R) – Allows you to write onto specially manufactured
disk. Once the information is stored on this disk it cannot be changed. This CD can store
up to 80 minutes or 700 MB of data.
Compact Disk Rewritable (CD-RW) – Data can be read and written to the disk.
Information written can be erased many times.
Digital Versatile Disc (DVD) – It is faster and can hold more data than CDs. It can store
audio, video and data.
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DVD
Magneto Optical
While magnetic tape, floppy disk, hard disk uses electro-magnetism technology and the
newer storage devices uses that of light or the optical technology. Magneto Optical uses
both elector-magnetism and optical technology. This device is considered a hybrid.
Magneto Optical
The most common secondary storage devices for use with Microcomputers are the floppy
disk and the hard disk.
Recording Techniques Used by Different Secondary Storage Devices
Storage Device
Magnetic tape, Magnetic disk
CD, DVD
Magneto Optical
Recording Technique
Magnetism
Laser Optical
Magnetism and Laser Optical
Activity
1. Indicate the type of access method used by the following devices:
Device
Magnetic Tape
Floppy Disk
Hard Disk
Compact Disk
DVD
Magneto Optical
Access Method
2. Create a table showing different types of magnetic and optical secondary storage
devices.
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