Secondary Storage:Architecture 2
- Created by: GamerGeorgie
- Created on: 05-02-18 10:02
Why is Secondary Storage needed?
It is backing storage that is external to the CPU, it stores data and programs and is non-volatile (i.e. when the computer is switched off, the backing storage will not lose its memory.
What is a storage device?
Storage is the act of storing something. A storage device (SD) is a device for storing data. It can hold data on a permanent or semi-permanent basis
What are the three forms of media?
Flash (e.g. USB)
Magnetic (e.g. hard disk or tape)
Optical (Shiny) (e.g. CD, DVD, HD or Blu Ray)
What is a Magnetic Disk?
Tapes or disks are coated with a magnetic surface used for storing electronic data.
Data is stored using magnetisied spots.
6GB hard disk drive contains over six billion spots.
Direct across medium.
Two types- Floppy disk and hard disk.
Features Hard Disks (Fixed)
Series of metal disks (platters).
Each surface has read/write heads.
Data from one file is stored on different surfaces.
Read / write heads work independently.
Fast data transfer speed.
It is a form of magnetic disk.
They are standard in most computers.
They have a capacity of 40-300GB+
Cost; £50 for 120GB Hard disk.
Uses of Hard Disks (Fixed)
Holds the application and operating system software
PPQ: Explain how data is written to and read from
The hard disk contains a stack of platters/disks
...and a set of read/write heads
Data is written magnetically
...in sectors
...in tracks
...in clusters
[1] for each of five points.
Zip Disk Features
More tracks and sectors than a floppy disk
Portable and faster data rate than floppy.
Capacity 100-200MB
Cost £9 (cheap)
JAZ Disk similar with 2GB
Zip Disk Uses
Hold a larger application (e.g. a database)
Backs up files on a personal computer.
DAT Tape (Magnetic Tape)
Digital Audio Tape- used for back-ups
Light and removable but can be slow.
Capacity can be 20-200GB - Cost £14.
A tape streamer uses a magnetic tape cartridge to store data.
A tape streamer is often attached to a server in order to make periodic data backups.
Uses of DAT Tape
Backup a server or network information.
Storage for large programs or files.
Optical Disks
Optical: high-capacity stroage medium that is read/write by a laser light.
Binary computer data are represented by the way the disk reflects light.
Optical diska are portable.
Direct acced medium.
Two-types: CD & DVD
Compact Disk (CD)
Optical media, can be CD-ROM; CD-R; CD-RW
Data is burnt onto surface using a laser.
Capacity is 700MB
Cost £1
Uses of Compact Disk
Holds a program or large files e.g. a database.
Holds music and large image files.
Backup personal files on a computer.
PPQ: Explain how data is read from and written to
A laser is used;
...to heat areas of organic dye layer
...to permanently
...change the reflectively of those areas
A lower powered laser reads the data
...be detecting alternating regions of heated and unaltered dye.
[1] for each of the three points.
PPQ: Explain how data is written to and read from
A laser is used;
...to temporarily
...modify the phase change properties of a dye
...between crystal phase (erased) and amorphous phase (recorded)
A laser detects the difference between resulting light and dark areas.
[1] for each of three points.
PPQ; Explain how data is written to and read from
A laser beam is used to read the data,
On a read-only DVD, pits are pressed onto the surface,
These are detected by changes in the intenisity of the reflected laser beam.
On a DVD-R or DVD+R, the laser burns/heats the dye on the surface of hte DVD.
...changing its reflectivity.
On a non-rewriteable DVD, the writing laser is more powerful than the reading laser.
[1] for each of four points.
Dual-Layer Disks
Dual layer disks are DVD's that have multiple layers
They have a semi-transparent extra layer over the same side of a disc.
The player acknowledges the shift from one layer to the next with a momentary pause.
Features of Digital Versatile Disk (DVD)
Optical media; DVD; DVD-R; DVD-RW
Excellent quality and fast data speed.
Capacity 4.7-17GB
Uses of a DVD
Can hold a program or large files e.g.a database.
Holds music or large image files
Holds a feature length film.
HD DVD (High-Density DVD)
A high capacity storage medium. A single-layer HD-DVD provides up to 15GBs (GB) of storage capacity.
Triple layer HD-DVD provides 45GB of storage capacity.
Blu-Ray
Can store even more data than a DVD
-A single layer disk can hold 25GB
-A double layer can store up to 50GB.
Only a dedicated Blu-Ray player can play them.
They are mainly used for storing high quality commercial movies. But you can buy a Blu-Ray burner for a pesonal computer and write-able blank Blu-Ray disks.
PPQ: Blu-Ray Advantages
The format was developed for high-definition video (HD) and for storing large amounts of data.
...permitting high definition audio and video/providing clearer pictures with improved colour and vividness.
[1] for each of two points.
PPQ: Blu-Ray Disadvantages
Blu-ray is a new/emerging technology.
...and players and discs are still relatively expensive.
...the range of films is restricted.
[1] for each of two points
Flash Memory Stick
Not optical or magnetic- connects to USB.
Works like RAM - solid chips.
Data is retained when switched off.
Capacity 128MB - 2GB+ (growing)
Cost: £20+
Flash Memory Stick Uses
-Hold a range of large files e.g. database
-Moving from one computer to another (presentations).
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