Database Management Systems 3ed, R. Ramakrishnan and J. Gehrke1 Indexed Sequential Access Method.
AS ICT. Identify suitable uses of common storage media understand the types of access and access...
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Transcript of AS ICT. Identify suitable uses of common storage media understand the types of access and access...
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Storage Media & Devices
AS ICT
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Objectives
Identify suitable uses of common storage media
understand the types of access and access speeds required for each use (e.g. serial/sequential, direct/random)
Describe the comparative advantages and disadvantages of using different backing storage media
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Devices vs Media
What’s the difference between a storage device and storage media?
The media is where the data is stored – eg the CD ROM, the magnetic tape, the barcode.
The device is the equipment that is used to store the data on the media – eg the CD writer, the magnetic tape deck, the barcode scanner.
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Types of storage media
Magnetic Optical Solid state Hybrid
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RAM vs Backing storage
When you are working on a computer, the data (and the programs) are stored in RAM.
However, this is volatile.
If you want your data to be available for future use, you have to save it permanently on some form of backing storage.
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Magnetic storage media
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Magnetic media
Data is stored on these in the form of magnetized bits.
Magnetic recording is a backbone technology of the electronic age. It is a fundamental way for permanently storing information.
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In the computer realm, magnetic recording is used on floppy disks, hard disks and magnetic tape as the main method for data storage.
Magnetic data storage is popular because it is an easy and inexpensive technology, with good medium-term (10 to 20 years) storage characteristics.
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Magnetic tape
These are very high capacity (can store massive amounts of data)
A tape can be written to instantly and kept for a long time, or the data can be erased and the media used again and again. Bit for bit, it is a much cheaper storage medium than CD-R DVD or Blu-Ray.
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Data storage
Data is stored on the tape in the order it is written:
Sequential - ie record by record.
Retrieval is therefore slow.
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Uses of magnetic tape:
Anywhere that requires extremely large capacity data storage where speed of retrieval is not an issue
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Batch processing: updating bank accounts with cheques
Producing utility bills etc – all customers’ bills are produced at the same time, and every record in the database has to be processed
Making backups – every item of data has to be read and saved
Payroll applications – all records have to be processed in sequence and at the same time
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Advantages of magnetic tapes
Bit for bit, cheaper than using disks
Very robust – the tape is encased in a cartridge
Easier to remove and keep away from the computer than equivalent storage media
Data transfer rate (ie putting the data on) is very fast
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Disadvantages
Access is very slow, so use is limited Updating files requires a new tape to
be created.
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Fixed hard disks
Industry standard for storing data on a computer
Used for storing software files and data files
Vary fast access to data, both reading and writing
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Data is stored randomly on the surface of the disk
Therefore access is Direct, or Random – this is much faster than serial/sequential access.
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Fixed hard disks: uses
Any system that requires fast data access times
Any system that requires fast data transfer speeds Real-time systems eg robotics, rocket
launching etc Online systems eg booking systems,
EPOS stock control, EFT File servers in computer networks
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Advantages:
Fast data transfer rate Fast data access times Very large capacity
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Disadvantages
Fixed hard disks are very easily damaged.
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Portable hard drives
Often used as a backup media
Also used for transferring large files from one computer to another
Large capacity – 1TB is now common
Often used for transferring server software from one network to another
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Advantages of portable hard drives
Fast data transfer rate Fast data access times Very large capacity
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Disadvantages
If dropped, they are easily damaged.
Transfer rats are not quite as fast as fixed hard drives
More expensive than other forms of removable media (eg CDs, DVDs etc)
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Optical storage media
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Optical devices
All optical devices operate by using a laser beam. The laser reads from and writes to the disk.
It etches the data onto the surface as microscopic ‘pits’.
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CD ROMS & DVD ROMS
Read Only Memory Can only be read from Cannot be written to DVDs can store about 10x
as much as a CD DVD writers use a shorter
wavelength of light, so pits are a lot smaller and therefore more data can be written onto a disk
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Uses
CD ROMs and DVD ROMs are used for applications which require the prevention of deletion of data (either accidental or otherwise) Software Computer games Music albums Reference books eg encyclopedias Storing films
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Advantages
DVDs hold more data than a CD CDs are cheaper to buy than DVDs Both hold much more data than a
floppy disk Both are cheaper than hard disks Both are more robust than hard disks
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Disadvantages
Data transfer rates are slower than hard disks
Data access times are longer than for hard disks
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CD-Rs/ DVD-Rs
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