1.6 - Secondary Storage

Secondary storage (also known as backing storage) is non-volatile storage used to hold data that can be accessed repeatedly. Because secondary storage is further from the CPU (and often external), it takes longer to access than primary storage.


Magnetic Storage

Magnetic storage includes devices such as magnetic hard disk drives (HDDs) and magnetic tape.


Magnetic storage is generally cheaper per gigabyte than other storage mediums such as solid-state storage.


This type of storage has a high capacity, with new desktop HDDs averagely containing 1TB of possible data storage.


Magnetic storage is often used for backing up files because of the high capacity.


Reading from magnetic storage or writing to it is slower than solid-state storage because of the moving parts.


Optical Storage

Optical storage uses laser technology to read data from a disc, such as a CD, DVD or Blu-Ray.


Optical media is cheap to bulk purchase, and because it is so thin, it is very portable


Optical storage is typically used for entertainment media, such as music CDs, movie DVDs and games.


A drawback of the thinness of a disc is the tendency it has to snap or become scratched to the point of data corruption.


Optical storage has a low capacity - less than 1GB on a CD and less than 5GB on a DVD.


Optical Storage

Solid State Storage

Solid-state (also known as flash) storage includes devices such as USB sticks, memory cards and solid-state drives (SSDs).


Solid-state storage is the fastest secondary storage medium because it contains no moving parts, so it can read and write data very quickly.


Solid-state devices are usually external, so they are portable and can be carried on a person in a pocket or a bag. 


A drawback is that solid-state storage is more expensive per gigabyte than magnetic storage; a 1 TB SSD can be twice as costly as a 1 TB HDD.


Solid State Storage

Cloud Storage

When you store data in 'the cloud', using services such as Google Drive or Dropbox, your data is stored on large servers owned by the hosting company. The hosting company (such as Google) is responsible for keeping the servers running and making your data accessible on the internet.

Cloud storage is typically free for a certain amount of room. For example, as of 2020, Dropbox allows 2 GB for free or 2 TB for £9.99 a month.

Cloud storage is very convenient as it enables people to work on a file at the same time, and it can be accessed from different devices. However, if the internet connection fails, or the servers are attacked then the data could become inaccessible


Data Storage Units


A single character can be represented in 1 byte

1 bit = 0 or 1

1 nybble = 4 bits

1 byte = 8 bits

1 kilobyte = 1,024 bytes

1 megabyte = 1,024 kilobytes

1 gigabyte = 1,024 megabytes

1 terabyte = 1,024 gigabytes

1 petabyte = 1,024 terabytes

1 exabyte = 1,024 petabytes

A kilobyte can store about a paragraph of text.

A megabyte can store about 1,000 paragraphs - roughly a small book.

A massive amount of data, a petabyte could store half a trillion pages of text.

Now a common hard drive size, a terabyte can store about 300 hours of video.

A gigabyte can store as much as two full CDs of music or video.

Questo's Corner

Secondary Storage:

a. For magnetic, optical and solid-state storage, rank these three secondary storage mediums in terms of capacity, durability, portability and speed.

b. For the following scenarios justify which secondary storage medium should be used and why it is the most appropriate:

     1. Sending videos and pictures to family in Australia through the post.

     2. Storing a presentation to take into work.

     3. Storing project files with other members of a group to work on together.

     4. Backing up an old computer with thousands of file to a storage device.   

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