CBCT2203 - Topic 4
CBCT2203 - Topic 4
CBCT2203 - Topic 4
Basic Concepts of
Information technology
Topic: 4
Secondary Storage
Objectives:
Secondary storage:
Storage
Tape
CD/CD-R/ DVD Smart
Flash CD-RW Media
drive
Examples of Removable
hard-drive
secondary
storage
Floppy
disk
Micro
Drive
PC card
Zip Disk Memory
Stick Smart Online
Card Storage Site
Secondary Storage:
Characteristics Advantages
Size • Can accommodate large amounts of data
• Data stored can reach gigabyte (GB) or
Terabyte (TB)
Reliability • It can be considered safe
Comfort • Data can be accessed immediately
Economic • Storage costs can be reduced
Lifetime • It is permanent and can be used for
archiving
• Some storage has a lifespan of up to 100
years
Magnetic Storage Devices
Hard Optical
disk Disk
Magnetic
tape
Flash
Memory
Storage
Cloud
Storage Other Types
of Storage
Magnetic Storage Devices: Magnetic Tape
• A magnetic tape is a thin plastic tape that has been covered with materials,
which can be magnetised
• Data are stored inside the tape roll and is represented by magnetic particles
that are digital data in discrete forms of “0” and “1”
• A tape contains a number of tracks (normally 7 or 9 tracks) or channels
used to store data
• Data on the tape will be deleted before new data is written on it
• Every tape column will represent one character
• Disadvantage: slow rate of serial data access
• Advantages: cheap, portable and long lasting
Magnetic Storage Devices: Hard Disk
• Contains one or more inflexible, circular, thick and strong metallic platters
that use magnetic particles to store data, instructions and information
• Disk is enclosed in an airtight, sealed case to protect it
• A hard disk that is mounted inside the system unit of a computer is called
an internal hard disk and not as portable as the external hard disc
• An external hard disk is a separate hard disk that connects with a cable to a
USB port on the system unit or communicates wirelessly
• Meanwhile, a removable hard disk is a hard disk that you insert and remove
from a drive
Magnetic Storage Devices
• Uses the principle of light, rather than the magnetic principle of storing data
• The emission of a laser beam determines the data to be written or read
• During the writing of data onto the surface of an optical device, a high
powered laser beam is used to form microscopic holes (pits) on the disc
• Each pit represents data “0” while part of the disc without a pit represents
data “1”
• During the reading of the optical disc, a low powered laser beam is directed
on the disc surface
• A reflection of the laser beam depends on the holes/ pit on the surface
• Four types: CD-ROM, CD-R, CD-RW and DVD
Storage Devices: Optical Storage
• Flash memory storage is a type of solid state media which consists entirely
of electronic components, such as integrated circuits; contain no moving
parts
• It is more durable and shock resistant compared to other types of media
such as magnetic hard disks or optical disks, due to lack of moving parts
• Example of flash memory storage:
- Solid State Drives (SSD)
- Memory cards
- USB flash drives
Storage Devices: Flash Memory Storage
Field Smith
Character/Byte
S (8 bits)
Bit
01010011
Upgrade Performance
3) Compressing/Decompressing Files
• This is required to remove excessive spaces from the computer files that
have reduced total available storage space
• Compressed files need to be decompressed before they can be used
• Normally data that has been compressed has a special suffix, such as .zip
and .rar
• Compression and decompression techniques are called “codec”
• Two main techniques:
- Lossless: data compression is done by preserving all input data
- Lossy: removes data permanently during the compression process but
users will not feel any loss