Storage Devices and Media

Syllabus Contents he syllabus says that you should be able to: describe common backing storage media and their associated devices:

magnetic tapes, CDs (all types), DVDs (all types), DVD-RAM discs, HD DVD discs, Blu-Ray discs, hard discs, memory sticks, flash memory

identify typical uses of the storage media, including types of access (e.g. serial/sequential, direct/random) and access speeds;

describe the comparative advantages and disadvantages of using different backing storage media;

define the term backup and describe the need for taking backups; describe the difference between main/internal memoryand backing storage,

stating the relative benefits of each in terms of speed and permanence.

Main MemoryMain memory (sometimes known as internal memory or primary storage) is another name for RAM (and ROM).

Main memory is usually used to store data temporarily. In the case of RAM, it is volatile (this means that when power is switched off all of the data in the memory disappears). 

Main memory is used to store data whilst it is being processed by the CPU. Data can be put into memory, and read back from it, very quickly. 

Backing StorageBacking storage (sometimes known as secondary storage) is the name for all other data storage devices in a computer: hard-drive, etc.

Backing storage is usually non-volatile, so it is generally used to store data for a long time.

Backing up dataBacking up refers to copying files of stored data onto separate storage medium in case of a problem with the main storage medium.The backups are often stored in a different place to the current location.

Reasons for backing up dataData could be lost due to the failure of the

original device e.g a head crush, possible corruption of files

Hackers could be responsible for corruptionIn case the files must be used while at the

same time protecting the original filesN.B Backing up data does not necessarily protect against viruses.

Types of accessSerial AccessDirect access

Serial AccessIn this system access to data starts at the beginning until the required information is found. It is used mainly on magnetic tape systems. Speed of access and order are not important.In magnetic tapes a new tape is required to update information.Old information is merged with the new data.

Direct AccessIt is used with magnetic disks and optical media. The computer uses a program to calculate the position where data is stored and it is accessed directly. It is used in applications where access speed is vital like online and real-time process systemsWhen updating data the new data is written to the next available location and the position recalculated.

Types of Backing Storage MediaBacking storage ensures that data is stored permanently and can be accessed later. It can be internal or external.MagneticOpticalSolid state

Magnetic tapesMade of thin strips of plastic coated with a

magnetic layer. It is fed through a read/write head. Data is stored as magnetised bits and accessed sequentially.

Uses- Used when large storage capacities are required and speed is not critical e.g batch processing cheques, Utility bills, payrolls and backups.

AdvantagesCheaper than other storage mediaRobust- encased in a cartridgeData transfer rate is fastCan easily be kept away from the computer

DisadvantagesAccess is slowUpdating files requires a new tape

Fixed hard disksFixed inside the computer and has platters on

which data is written. It stores important programs on the computer such as operating systems. They are used by an program that requires fast access to data e.g real-time systems in robotics,rocket lauching, online systems and on file servers

Advantages and DisadvantagesAdvantages

Data transfer rate is fastData access times are fastLarge storage capacity

DisadvantagesThey are fragile

Portable hard disksThey are similar to fixed hard disks and can be

connected and disconnected from a computer easily

Uses-They are used as backup media or for transferring server software from one computer to another.

Advantages and DisadvantagesSimilar to fixed hard disks but are slower when

accessing data and more expensive

Prep- Do notes on the remaining storage devices

Optical Backing Storage MediaThey operate using a laser beam. It reads from

and writes to the disk. The disk is polycarbonate plastic covered in reflective material. This is etched into using a laser beam. The ‘pits’ formed represent the data.

CD ROMS/DVD ROMSThe main difference is their storage capacity.

DVDs use a shorter wave length of laser light than CDs.

They are used for applications which require the prevention of the deletion of data.

List examples of uses.

Adv. And Disadv. Adv-DVDs hold more data than CDs-CDs are cheaper-Both are more robust than hard disksDisadv-Data transfer rates are slower for both CDs

and DVDs-Data access times are longer

CD Rs/DVD RsA laser beam causes spots on the dye to be

heated up and the reading process distinguishes between the heated and unheated spots.

Used for home recordings of cds and dvdsAdv-Cheaper-Cannot be accidentally written overDisadv-Can only be recorded once-Not all CD players can read CD Rs

CD RWs/DVD RWsThe recording surface is a metallic alloy layer.

It can exist in anamorphous state or a crystalline state

Adv-Can be used more than once-Different versions of files can be overwrittenDisadv-They are expensive-Files can be overwritten accidentally

DVD RAMsThis is a newer technology. Data is stored in

concentric tracks like magnetic media.They have quicker access times and an in built

data check to ensure that data is written correctly.

Used in camcorders, archiving and general data storage.

Adv and DisadvAdv-They have a bigger storage capacity-More durableDisadv-Not compatible with most DVD players-Expensive

Blu-ray disksThey have the largest storage capacity: 25, 50 and 100

Gb. They use a shorter wave length laser beam using light that is close to the blue/violet spectra.

Uses-games consoles, camcorders, entertainmentAdv-Large storage capacity-Data transfer rates are high-Access speeds are highDisadv-Expensive-Problems with encryption techniques for preventing

piracy

MinidisksUses magnetic and optical technologies for recording

data. One site is heated and the other side is magnetised. It can be wrtten several times. The disk is permanently housed in a cartridge.

Used in portable music playersAdv-Can be recorded over many times-RobustDisadv-Transfer rates are slower-Hold less data-Expensive

Solid State Backing StorageThey are made of silicon chips consisting of

rows and columns of cells. Each cell is made of two transistors separated by a thin oxide layer. They have no moving parts. The cell has a value of 1 or 0 depending on its charge.

Memory Sticks or pen drivesConnected to a computer via the usb port.

Used for transporting files and software fixes.Adv-Compact, robust and do not need drivers to

operateDisadv-Cannot be write protected-More expensive/Gbyte of storage