S4C Catherine Cho
Red Yeung
Jessica Tsang

◎ Also called “Backing storage”
◎ Store data, operating system and application software
◎ Non-volatile
◎ Measured by access time and data transfer rate
◎ Can be classified into 2 main types
◎ Magnetic storage devices
◎ Optical storage devices

Secondary storage device
Main Memory
CPU

Description
Access time The time to search and read the data
Example
8ms – 20ms
Data transfer rate
The amount of data that can be transferred per second
44.2 MBps – 111.4
MBps
Data transfer rate Searching speed
Reading/writing process Access time

Unit
Kilobyte
Megabyte
Gigabyte
Terabyte
Abbreviation
KB
MB
GB
TB
Value
1KB =2 10 B
1MB =2 20 B
1GB =2 30 B
1TB =2 40 B

Magnetic storage devices
Optical storage devices
The Concept Electromagnetism Optical reflection

◎ Most of them  read/write enabled
◎ E.g. floppy disks, hard disks, magnetic tape s

◎ Only have 1.44 MB
◎ Usually used for backing up and transferring a small amount of data
◎ Direct access mode

Advantages
◎
Handy
◎
Cheap
◎
Rewritable
◎
Removable
Disadvantages
◎
◎
Small capacity
Data transfer rate
◎
Often unreliable
◎
Can not used in all computers
◎
Short-aged

◎ Have one or more circular disks
◎ Called platters
◎ Each platters have a large number of tracks
◎ Direct access mode
◎ Fast, durable, high-capacity storage medium

The data transfer rate
The time of access data file
The rotational speed
The time of access data file
The speed rotations of disk plates
The movement of read/write heads

◎ Sequential access mode
◎ For back up purpose
◎ Latest magnetic type = DAT
◎ Storage over 72GB
◎ Low cost

◎ Most of them --> store data, instructions
◎ E.g CD-Rom, CD-R, DVD ,DVD-R

◎ Data stores and accesses by via red laser
◎ The content --> permanently
◎ Data represented by pits and lands

P.78 PICTURE

◎ The speed --> its data transfer rate
◎ direct proportion
◎ Measured relative to use 2x, 4x, 8x, etc
◎ To describe the speeds

◎ Both CD-R drives and CD-RW drives
◎ Allow to write data
◎ CD-RW can rewrite data many times over

◎ Store up to 17GB of Data
◎ Can saved movies and libraries of multimedia files
◎ Many different variations
◎ DVD+R, DVD-R, DVD+RW, DVD-RW, DVD-
RAM
◎ The concept of write data on to DVD same with a floppy disk
◎ To copy, modify and delete files
◎ The speed to write over 8x

Drive Can read data from
CD-ROM drive
CD-ROM, CD-
R, CD-RW
CD-R drive CD-ROM, CD-
R, CD-RW
CD-RW drive CD-ROM, CD-
R, CD-RW
DVD drive CD-ROM, CD-
R, CD-RW
Can write data onto
CD-R
CD-R, CD-RW
DVD+R,
DVD-R,
DVD-RAM
Can modify data to
CD-RW
DVD+RW,
DVD-RW,

◎ For storing digital media
◎ Used the blue-violet laser technology
◎ Are incompatible

CD-ROM
CD-R
CD-RW
DVD
DVD-R
HD DVD
Blu-ray Disc
Storage capacity
Single layer Dual layer
750 MB
700 MB
650 MB
4.2 GB
15 GB
25 GB
17 GB
8.4 GB
30 GB
50 GB

CD-ROM
CD-R
CD-RW
DVD
DVD-R
HD DVD
Blu-ray Disc data transfer speed
150 KBps
1.32 MBps