Secondary storage and it’s need

Secondary storage, in terms of computing, refers to a non-volatile storage device on a computer. Non-volatile means that it is a storage device that enables permanent storage; data isn’t lost after power is lost.

RAM (see chapter 1.2), ROM (see chapter 1.2) and CPU cache (see chapter 1.1) are all counted as primary storage. Other storage devices, such as the hard drive in a computer, or a USB flash drive, is counted as secondary storage.

Secondary storage, in short, is a semi-permanent storage method (files can be edited at the will of the user), and stores programs and files when the power is turned off.


Beyond GCSE Information

Tertiary storage is a storage medium that is for archival purposes. An example would be a tape format, where data is dumped onto this storage format, and stored away for backup purposes.

Data capacity

As a recap from the Data Representation chapter, when refering to the capacity of a storage medium, it is referring to how much data it can hold. This is measured in bits.

A bit is the smallest unit of data in a computer system. A bit is a single binary value, represented by either a 0 or a 1. You can put a bits together, to make larger units of data, such as nibbles and bytes.

Bits can be converted into different capacities, as shown below:

  • 4 bits in a nibble

  • 8 bits (2 nibbles) in a byte

  • 1000 bytes in a kilobyte

  • 1000 kilobytes in a megabyte

  • 1000 megabytes in a gigabyte

  • 1000 gigabytes in a terabyte

To be able to go from a bit, to a terabyte, you do 8*1000*1000*1000*1000, or 8*1000^4. A recommendation is to write out each of the steps, going from a bit to a terabyte, and then following each step until you get the correct answer.

Data types

In terms of file sizes, you won’t have to know specific file sizes for any data type. However, you will need to know how large files are, in relation to one-another. The list below (from smallest size to largest) is the general size of different file types:

  • Word Documents (Smallest)

  • Image files

  • Sound files

  • Video files (Largest)

File compression will play a factor in file size. You can read more about this in chapter 2.6.

Data types

Optical storage

In optical media, the disc drive uses a laser, and this shines onto the surface of the disc. The reflection is processed by the drive, into binary data.

Optical storage

Beyond GCSE Information

When writing data, the disc has small recessed areas burned in. These recessed areas are microscopic, and are referred to as a 'pit'. When the laser is shot at a pit, it shatters and no reflection is sent back. A binary digit of 1 is represented by a pit. If no hole is burned, then this is called a 'land', where the laser is reflected. A land represents a 0.

Different types of optical media exists, ranging in capacity.

  • CD-R is a read-only optical disc. This medium became popular for storing music bought from stores.

  • CD-RW is an optical disc that allows the consumer to write their own data onto the disc. This medium became popular as a way to make backups of your music.

  • DVD-R is a read-only optical disc. This medium became popular for storing standard definition video and movies.

  • DVD-RW is an optical disc that allows the consumer to write their own data onto the disc. This medium was more useful than CD-RW for a backup method, as it had a larger capacity.

  • Blu-ray is an optical disc, that has a large capacity for optical media. This became popular as HD video and movies became more commonplace in a household.

Optical storage mediums have their place, for instance:

  • Optical media is extremely cheap to produce, making it great for distributing music and video.

  • Discs are thin and portable, making them easy to store.

However, there are some massive drawbacks to optical media:

  • It is slow to access data on an optical disc.

  • Compared to magnetic storage and solid state storage, the capacity is much lower on optical media.

Magnetic storage

Magnetic storage drives have a physical platter, or disk, with many particles with a magnetic charge. This charge can be read by a read and write head, and is turned into binary 0s and 1s.

Magnetic storage

Beyond GCSE Information

Magnetic storage drives have iron particles that, depending on it’s polarity (based on the north and south poles of the magnet), can represent binary digits. A magnetic read head travels across a this surface, known as a platter, and reads the polarity.

The most common type of magnetic storage today is a hard disk drive, or HDD. However, floppy disks and tape drives also use the same concept.

There are quite a few benefits of mechanical storage:

  • It is extremely cheap compared to the alternatives, for large capacities.

  • Compared to optical media, it is fast to access data.

  • Unlike an SSD, there is not a limited number of write cycles.

However, magnetic storage does have it’s drawbacks:

  • Although it is faster than an optical disc, it is still slower than solid state storage, as there is a moving head that physically has to travel across the drive.

  • Moving parts eventually fail.

  • Data can be scattered across the platter, and as such, needs defragmentation to perform it’s best. This takes time to perform.

Solid state storage

Solid state drives have no moving parts, and use electrons to represent binary digits, by knowing whether the electron is charged or not.

Solid state storage

Beyond GCSE Information

Solid state drives work via a flow of electricity, that can force electrons in a floating gate transistor to either be charged or not-charged, representing binary data as a 0 or a 1. These floating gates are between two oxide layers. This is organized as a grid, and this is referred to as a 'block'. Individual rows in this block are referred to as a 'page'.

Solid state is used in different storage devices. A solid state drive is an alternative to a traditional mechanical hard drive. It is also used in memory sticks, or flash memory cards, along with usage in mobile phones.

The benefits of solid state storage is immense:

  • It is much faster than optical or mechanical to access data.

  • Since there are no moving parts, it will not be damaged via motion or vibrations, making it better for small devices that are moving around like smart phones or digital cameras.

  • There is no need to defragment the drive, unlike hard drives.

  • It is low power, as there are no moving parts.

  • As there are no moving parts, there is no noise.

However, there are some drawbacks to solid state storage:

  • Solid state drives are also much more expensive.

  • A limitation of solid state media, is that the oxide layers can deteriorate, causing the media to become unreliable. This means there are a certain number of read and write cycles available to the solid state chip.


Different characteristics can affect which storage medium a product manufacturer places into their device. The factors below are to be considered in a question about storage mediums:

  • Cost - how expensive is it?

  • Capacity - how much data can be stored on it?

  • Speed - how fast is the access to this data?

  • Portability - how large is the medium, in physical size?

  • Durability - how strong is the media, in terms of physical conditions like heat and shocks?

  • Reliability - can it be written to, and read from many times, without failing?

Depending on the situation, depends on which medium should be utilized.

For instance, a band who want to distribute their music will most likely choose optical media, as it is cheap to manufacture, and can store a full album.

A digital camera, on the other hand, should use a flash storage medium. This is because the camera will be moved around (and this would damage any moving parts), and is fast to write photos onto. It is also very portable, as it is small.

A final example would be a desktop computer, designed to play video games. Magnetic storage would be utilized, as it is cheap for large storage capacities. This means that large video games can be stored on, for cheap, and not take up a huge chunk of the storage of that drive.

A question may ask about a certain situation, and will expect you to analyse all three formats, and pick the most suitable option. This will require you to make a conclusion about which is the best for the application.

Although there is a specific answer they are looking for, as long as you justify your answer with correct analysis of the above characteristics, and conclude based on those factors, you will gain the marks.

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1.3 Memory

1.5 Systems Software