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Ch.13 Secondary Storage Devices - Coggle Diagram
Ch.13 Secondary Storage Devices
13.1 Secondary Storage Devices
✧ Store data, operating system and application software on a computer system.
✧ Also called backing storage.
✧ Non-volatile
✧ The speed of a secondary storage device is affected by access time data transfer rate
Unit
13.2 Magnetic Storage Devices
Floppy disks
● A piece of circular flexible plastic disk with magnetic coating
● Sealed inside a square protective casing
● 3.5-inch magnetic disk
● Storage capacity: 1.44MB
● Stores data in tracks and sectors
● A floppy disk drive is used to access the data on a floppy disk
● Largely replaced by other portable storage media
Hard disks
● Platters
⬥ One or more circular disk of a hard disk
⬥ Made of aluminum, glass or ceramic with a magnetic coating
⬥ Each side of the platter consists of a large number of
__
tracks
__
and sectors
⬥ Read write head is responsible for accessing the data on one platter surface.
● Direct access
⬥ Access arm moves the read/write head on the platters.
Magnetic types
● Magnetically coated strip of plastic on which data is stored
● Sequential: has to move consecutively through all preceding data before it can access the desired data
● Relatively slow
● Used only for backup purpose
● Allow users to store or transport a lot of data at low cost.
Magnetic storage device
◆ Data is stored as electromagnetic charges on the magnetic surfaces of these storage devices.
◆ Most are read/write enabled.
Optical storage devices
◆ Store data and instructions as microscopic pits on disk surfaces
◆ Examples: CD-ROM, CD-R and DVD
✧ Rewritable media
● Store data in integrated circuit chips.
● Magnetic coating on magnetic media gradually loses their magnetic charge, resulting in data loss.
● Susceptible Environmental damage
13.3 Optical Storage Devices
Compact disc read-only memory (CD-ROM)
● 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 permanently when it is manufactured.
●optical disk : a device that reads data from 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.
● Reliable and inexpensive
● Speed
● Hold about 750 MB of data
13.4 Other Forms of Secondary Storage Devices
Magneto-optical (MO) disks
● Use a combination of magnetic and optical methods to read and write data from 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.
Memory cards
● Made up of small memory chips on a card
● Hold data in an electronic format.
● Extend the storage capacity of a wide range of portable electronic devices, e.g. digital camera, mp3 player, mobile phone.
● Memory card reader : provide data transfer connection between a memory card and a computer.
● Storage capacities: few MB – 64 GB
USB Flash drives
● Compose of an internal memory card and an USB interface adapter.
● Storage capacity up to 1TB
● Some of them provide security controls such as password protection system and a fingerprint identification system.