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CH.13 Secondary Storage Devices - Coggle Diagram
CH.13 Secondary Storage Devices
13.1
Secondary Storage Device
Usage
Store data
back up data
Speed
Acess Time
Description
It is the average time taken for the device to search and read the required data on the storage medium .
Shorter access time means higher searching speed
Example
8 ms to 20 ms (Note: 1 ms = 0.001 second)
Data Transfer Rate
Description
It is amount of data that can be transferred between main memory and a storage device per second
The higher the data transfer rate, the faster the reading/ writing process is
Example
44.2 MBps to 111.4 MBps
Capacity
KIlobyte (KB)
1 KB = 2^(10)B = 1024 B
Megabyte (MB)
1 MB = 2^(20)B = 1024 KB
Gigabyte (GB)
1 Gb = 2^(30)B = 1024 MB
Terabyte (TB)
1 TB = 2^(40)B = 1024 GB
Categories
Magnetic Storage Devices
Example
Floppy Disk
Hard Disk
Magnetic Tapes
Properties
stored as electromagnetic charges on the magnetic surfaces of these storage devices
Most are read/ write enabled
optical Storage Devices
Properties
Store data and instruction as microscopic pits on disk surfaces
Rewritable media
Store data in integrated circuit chips
Magnetic coating on magnetic media gradually loses their magnetic charges, resulting in data loss
less snsceptible to environmental damage
Other types of storage devices
Example
Memory cards
USB storage device
Example
CD-ROM
CD-R
DVD
13.2
Categories
Floppy disk
A pieces of circular flexible plastic disj with magnetic coating
Store data in tracks and sectors
Sealed inside a square protective casing
3.5 inch magnetic disk
1.44 MB Capacity
Access the data on a floppy disk
Access the data and transfer a small amount of data between computers
Largely Replaced by other portable storage media
Hard disk
Platters
Read/write head is responsible for accessing the data on one platter surface
Made by aluminium , glass or ceramic
One or more circular disk of a hard disk
Each side of the platter consists of a large number of tracks and sectors
Direct access
Access arm moves the read/write head on the platters
The drive then rotates the platters to the proper position
The platters and the read /write heads are sealed in a metal case to keep dust and moisture out
Seek time = the time take to move the read/write head over the right track and sector to get ready for data transfer
Data rotational speed = number of revolution the disk platters make per minute (unit revolution per minute, rpm)
Fast, durable and high-capacity
Magnetic types
Magnetically coated strip of plastic on which data is stored
Sequential access the desired data
Relatively slow
Used only to store or transport a lot of data at low cost
13.3
Compact disc read-only memory
A round plastic disk coated with a metallic surface
Data can be stored and accessed via red-light laser technology
Content of a CD-ROM is set permanetly when its manufactured
CD-ROM
a device that reads data form a CD-ROM
Data stored is represented by pits and lands on the reflective layer
CD-ROM drive focuses a laser beam on the layer so as to read the stored data
Hold about 750 MB
Reliable and inexpensive
Speed
Measured in terms data transfer rate
Single-speed drive could transfer 150 KBps of data
Two variation of the standard CD-ROM
Compact disc rewritable
Compact disc-recordable
Digital versatile disc (DVD)
Can store up to 17 GB of data
DVD Drive
A device that reads data from a DVD, CD-ROM, CD-R and CD-RW
More advanced optical disk format originally designed for the storage of full-length features films
Many variations
DVD+R, DVD-R
write once and read only
DVD+RW, DVD-RW
write and read repeatedly
DVD-RAM
Allows data to be written and rewritten and allows users to copy, modify and delete files
1x speed rating for DVDs is 1.32 MBps
High-definition digital versatile disc(HD DVD) and Blu-ray DIsc
Both use the blue-violent laser technology
HD DVDs and Blu-ray Discs are incompatible with each other
Both are high-density optical disc formats
13.4
Categories
Memory cards
Hold data in an electronic format
Extend the storage capacity of a wide range of portable electronic devices
Example
digital camera
mp3 player
mobile phone
Made up of small memory chips on a card
Storage capacities
few MB - 64 GB
Memory card reader
Usage
provide data transfer connection between a memory card and a computer
USB Flash drives
Storage capacity up to 1 TB
Some of them provide security controls such as password protection system and a fingerprint identification system
Compose of an internal memory card and an USB interface adapter
Magneto-optical (MO) disks
Use a combination of magnetic and optical methods to read and write data form and to the MO disk
Removable, Rewritable, store up to 9.1 GB of data
A reliable media that can hold data for over 30 years
13.5 Network Storage
A storage device which is not attached to a user
Accessed through ordinary networks
Common storage devices: Magnetic tapes and Hard disk
Provide additional storage space for individual computers
Act as a central storage in the case of a mainframe computersystem
Facilitate the sharing of information and storage management
Exist in the following form
Can be a storage system connected to a network
Network - attached storage (NAS)
Storage area network (SAN)
They provide much more powerful storage capabilities and management facilities
Can be a storage device directly attached to a file server in a network
Can store data in remote computers, such as Internet hard devices, AN internet hard drive is a storage space accessible through the internet
13.6 latest development of Secondary Storage Devices
Categories
Hybrid hard drive
Integrate flash memory to achieve shorter access time
Lower power consumption
Portable electronic devices
Example
Notebook computer may take such advantage to gain performance boost and longer life time
Blu-ray disc
New standard for high definition optical disc, will soon replace CD-ROMs and DVDs
Microdrive
A type of tiny hard disk
One of the essential storage components of handy electronic devices including smart phones, PDAs and portable media players