Storage Media & Devices

AS ICT

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

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.

Types of storage media

Magnetic Optical Solid state Hybrid

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.

Magnetic storage media

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.

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.

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.

Data storage

Data is stored on the tape in the order it is written:

Sequential - ie record by record.

Retrieval is therefore slow.

Uses of magnetic tape:

Anywhere that requires extremely large capacity data storage where speed of retrieval is not an issue

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

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

Disadvantages

Access is very slow, so use is limited Updating files requires a new tape to

be created.

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

Data is stored randomly on the surface of the disk

Therefore access is Direct, or Random – this is much faster than serial/sequential access.

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

Advantages:

Fast data transfer rate Fast data access times Very large capacity

Disadvantages

Fixed hard disks are very easily damaged.

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

Advantages of portable hard drives

Fast data transfer rate Fast data access times Very large capacity

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)

Optical storage media

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’.

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

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

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

Disadvantages

Data transfer rates are slower than hard disks

Data access times are longer than for hard disks

CD-Rs/ DVD-Rs