Transcript Ch.13 Secondary Storage Devices

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
Data transfer The amount of data
that can be
rate
transferred per
second
Data transfer rate
Example
8ms – 20ms
44.2 MBps – 111.4
MBps
Searching speed
Reading/writing process
Access time
Unit
Abbreviation
Value
Kilobyte
KB
1KB =210B
Megabyte
MB
1MB =220B
Gigabyte
GB
1GB =230B
Terabyte
TB
1TB =240B
The Concept
Magnetic storage
devices
Optical storage
devices
Electromagnetism
Optical reflection
◎Most of them  read/write enabled
◎E.g. floppy disks, hard disks, magnetic tapes
◎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, DVDRAM
◎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, CDR, CD-RW
CD-R drive
CD-ROM, CDR, CD-RW
CD-RW drive
DVD drive
Can write data
onto
CD-R
CD-ROM, CD- CD-R, CD-RW
R, CD-RW
CD-ROM, CDR, CD-RW
Can modify data
to
DVD+R,
DVD-R,
DVD-RAM
CD-RW
DVD+RW,
DVD-RW,
◎For storing digital media
◎Used the blue-violet laser technology
◎Are incompatible
Storage capacity
Single layer
Dual layer
CD-ROM
CD-R
CD-RW
750 MB
700 MB
650 MB
17 GB
DVD
DVD-R
HD DVD
Blu-ray Disc
4.2 GB
15 GB
25 GB
8.4 GB
30 GB
50 GB
CD-ROM
data transfer
speed
150 KBps
CD-R
CD-RW
DVD
DVD-R
HD DVD
Blu-ray Disc
1.32 MBps