Backing StorageWhy do we need backing storage?

Data and programs are stored in main memory temporarilyMain memory has a limited amount of storage space

Backing StorageWhy do we need backing storage?

Backing storage devices can be used to store large amount of data and programs permanently.

Note that backing storage devices are slower than main memory when storing and retrieving data.

Backing StorageBacking Storage Devices can be classed as:MagneticOpticalSolid State

Backing StorageMagnetic Optical Solid StateFloppy Disk CD Memory CardsHard Disk DVD USB Flash MemoryTape Solid State Drive

Magnetic StorageA hard disk (or platter) is a disk coated with magnetic materials.

The disk spins while the arm moves in and out.

Each magnetic field can then be manipulated to represented one of two states using a read/write head.

Floppy Disk DrivePortable 3.5 inch disc with a limited capacity of 1.4 Mb.

Hard Disk DriveFixed disk inside a computer or as an external portable drive

Has capacities up to several Terabytes

Magnetic TapeTape is very slow to access – access is linear.

Mainly used for backups.

Optical StorageThe information is recorded onto the disk in the form of pits and lands.

Pits are raised, lands are lowered.

Land

Pit

Optical StorageThe drive uses a lower powered laser to scan the disk as it turns.

The light is reflected from the pits and lands, on the disc surface, differently and it is this pattern of reflection that indicates the data read.

CD-ROMA CD-ROM disk is a read only medium whose contents cannot be altered once data is written to it.

Capacity of a CD is approximately 700Mb

CD-R CD-R drives allow CD-ROMs and audio CDs to be written to, but only one time.

CD-RW (Rewritable)CD-RW drives enable CDs to be written onto it in multiple sessions.

DVDDVD-R, DVD-RW, DVD+R, DVD+RW, DVD-RAM

DVDs use an optical technology that uses a higher laser wavelength than CD. This means that tracks can be smaller and closer together and pits in the surface can be smaller.

Capacity is either 4.7 or 8.4 Gb

Blu-RayBlu-Ray is the next generation of optical storage device

It uses a narrower laser (blue) than the laser used for CD / DVD (red)

Capacity is 27Gb or 54Gb

Access speeds range from 4.5 Mb per second to 54Mb per second

Solid State DevicesMade from Electrically Erasable Programmable Read-Only Memory (EEPROM)

Physically very small and portable

No moving parts therefore not damaged by movement

Beginning to be used in place of hard disk drives in computers

Memory CardsUsed for storage:•Digital cameras•Mobile phones•MP3 players

Standards include:•SD Card•Mini SD Card•Micro SD Card•Compact Flash•Secure Digital•Memory Stick/Pro•XD-Picture Card

Compact Flash SD Card Micro SD Card

Memory Card Reader• Allows Flash cards to be attached too a USB device.• Installed in some PC’s.• Allows data to be read from peripherals without the use of cables.

USB Flash Memory• EEPROM memory chip with a USB plug.• When it is plugged in, the computer will automatically recognise it and the

files can be transferred to and from the device.

Solid State Drive• SSD (Solid State Drive) hard drives are faster, more reliable and much

more efficient than normal hard drives• The flash memory used in SSDs is faster and more reliable than the flash

memory in USB drives • Data is stored on interconnected flash memory chips that retain the data

even when there's no power present• No moving components unlike traditional hard disk drive• This means they are more durable and able to withstand knocks• Many desktop computers now come with a hard disk drive and a

separate SSD. Common to install the OS on an SSD to allow faster start-up

Cloud Storage• The storage of data online in “the cloud”

• Data is stored in and accessible from multiple distributed and connected resources (servers) that comprise a cloud.

• The end user does not necessarily know where their data is stored

Cloud StorageAdvantages:•Accessible anywhere (with Internet connectivity)•Data Back-ups•Lower cost than buying hardware backing storage solutions

Disadvantages:•Potential security concerns

InterfacesBacking storage devices need to be able to connect to and communicate with the CPU. This is the job of an interface.

There are a number of commonly used interfaces, as follows:

•SATA 3.2 (16 GB / sec)•USB 2.0 (480 Mb / sec)•USB 3.0 (5 GB / sec)•Firewire (800 Mb / sec)•Thunderbolt 2 (20 GB / sec)