3 Storage devices and media

Backing up

Copying of files/ data to a different medium (e.g. disk, tape, flash drive, etc) in case of a problem with the main secondary storage device.

What are the types of access?

• Serial Access (Sequential Access)

• Direct Access (Random Access)

Serial Access (Sequential Access)

Finds data by searching storage media from the beginning of the media to the end until the data required is found. One example would magnetic tapes.

Direct Access (Random Access)

Data to be accessible immediately from storage media w/o checking the data from start to end. Examples of storage devices that use direct access would be magnetic hard disks, optical media such as CD and DVD.

Advantages of Serial Access

• Useful when every bit of data needs to be read off the storage device

• Used in batch processing systems (system where all the data on the storage device is accessed and then processed in turn).

Disadvantages of Serial Access

• Slow form of access when looking for particular data.

Advantages of direct address

• Used when fast access to the data is important such as online booking systems, systems for POS (point-of-sale) terminals in shops.

Disadvantages of direct address

• New data produced during updating stored anywhere on the disk (not able to find the data from the place we have last updated.)

Identify Storage devices

• Fixed/Internal hard disk drive (HDD)

• Portable Hard disk drives

• Magnetic tapes

• CD-ROM and DVD-ROM

• CD-R and DVD-R

• CD-RW and DVD-RW

• DVD-RAM

• Blu-ray discs

• Memory sticks/ Pen drives

• Flash memory cards

Fixed/Internal hard disk drive (HDD)

Uses

• To store OS, systems software and working data/files.

• Used in file servers for computer networks.

• Used in real-time systems (e.g. robots, control of chemical plant) and in online systems (e.g. booking airline tickets).

Advantages

• Fast data transfer rate and fast access time

• Large memory capacities

Disadvantages

• Easily damaged if shut down procedure is not carried out

• Many moving parts compared to SSD (solid state drives)

• Noisy read/write operation

Portable Hard disk drives

Uses

• Used as backup systems to prevent loss of data

• Used to transfer data/ files/ software between computers.

Advantages

• Fast access time & data transfer rate

• Large memory capacity

• A method of transferring data between computers.

Disadvantages

• Easily damaged if dropped

• Loss of data if incorrect shutdown procedure

Magnetic tapes

Uses

• Used as backup media

• Used in long-term archiving of data

Advantages

• Less expensive (per byte) than the equivalent hard disk

• Large storage capacity

• Faster data transfer rate than equivalent hard disk

Disadvantages

• Slower data access time than equivalent hard disk

• When updating, another tape is needed to store the final updated version.

CD-ROM and DVD-ROM

Uses -CD- ROMs store music files, software, computer games and reference software

• DVD-ROMs have larger storage and used to store films, computer data

Advantages

• Holds more data than floppy disks

• Less expensive than hard disk drive systems

Disadvantages

• Slower data transfer rate/data access time than hard disks

CD-R and DVD-R

Uses

• Home recordings of music (CD-R) and films (DVD-R)

• Used to store data to be kept for later use

Advantages

• Cheaper than RW disks

• Once burned-similar uses as ROM

Disadvantages

• Not all CD/DVD players can read CD-R/DVD-R

• They can only record once.

CD-RW and DVD-RW

Uses

• Used to record tv programmes, which can be recorded many times

• Not as wasteful as R format as more files/data can be added to at a later stage

• Used in CCTV systems

Advantages

• Can be written over many times

• Can use different file formats each time it is used

Disadvantages

• Can be relatively more expensive than DVD-Rs and DVD-ROMs

• Possible to accidentally overwrite data

DVD-RAM

Uses

• Used in camcorders to store movies

• Allow simultaneous recording and playback in recording devices

Advantages

• Have a long life (min. 30 yrs)

• Large capacity of about 10GB

• Can rewrite operation over 100,000 times

• Need to finalise the disk

Disadvantages

• Not as compatible as R or RW format

• Relatively expensive (four times higher cost than DVD-RW)

Blu-ray discs

Uses

• Home video consoles

• Storing and playing back movies

• PCs use disks for data storage or backing up hard drives

Advantages

• Larger storage capacity than CD/DVD-Rs and ROMs ideal for storing HD movies

• Faster data transfer rate compared CD/DVD-Rs.

• Data access rate is greater than other optical media

Disadvantages

• Encryption problems when used to store video

• Relatively expensive compared to other optical media

Memory sticks/ Pen drives

Uses

• Transporting files between computers

• Used as a backup storage

• Used as a security device

Advantages

• Compact and portable media

• Robust

• Not affected by magnetic field

Disadvantages

• Can't write-protect the data/files

• Easy to lose due to small size

Flash memory cards

Uses

• Storing photos on digital cameras = Used in MP3 players to store music files

• Used as mobile phone memory cards

Advantages

• Very compact & easy removal to use in another device

• Since they ares SSD (solid state drives), robust

Disadvantages

• Expensive per gigabyte of memory compared to hard drive disks

• Lower storage capacity than hard disks