We all want to store files over a long period of time. We keep photographs, projects, music, films, letters and spreadsheets on our computers. We also expect our programs to be there when we switch the computer on. This long term storage is sometimes called Secondary Memory or Secondary Storage (primary memory is the main memory). Secondary storage is usually much larger and, as we want such a lot of it, it needs to be cheap. Cheaper memory technologies tend to have slower access speeds than main memory, as discussed earlier. Secondary memory is non-volatile and needs to be robust and reliable. Has your memory stick been through the washing machine yet?! Choosing the right type of storage medium for a particular use is important. You need to consider the following features:


Magnetic Storage Devices

Optical Devices
Solid State


Internal Hard disk

Portable Hard disk

Magnetic tape

SSD / Flash


Very cheap but not as cheap as tape 1TB internal drive is approx. £70

Cheapest bulk data storage medium 72GB tape £8

Very cheap
Cheap for the capacity
Average price


Up to 8 TB

Up to 1 TB
740 MB
4.7 GB
25 - 50 GB

Up to 4TB SSD

500GB Flash

Access speed

up to

6 Gb/s

480 Mb/s speed of USB2 interface. 640Mb/s for USB3

Slow access speeds – tape reader has to work through the data serially

1x - 150 KB/sec

2x - 300 KB/sec

4x - 600 KB/sec

8x - 1.2 MB/sec

1.25 MB/sec
up to 650 MB/sec


Not portable built into the pc

Can fit into a pocket

Can be compact but needs a tape drive to read and write

Can be compact but requires a drive
Highly portable as they are light.


Good durability when the disk is not in use or being transported. You can write the disk an infinite number of times. Data can be lost in magnetic fields

Limited life cycle. Tape can deteriorate. Can be affected by heat and magnets.

Can last a reasonably long time with care.

Prone to scratches

up to 10 years


Limited life expectancy as the number of writes can decrease the usability.


Extremely reliable

Reliable if kept in good conditions

If scratched, the data might not be able to be read.

Needs a computer with a CD or DVD drive in order to read the disk.

No moving parts to damage.

No affected by magentic fields

Typical use

Inside a PC as secondary storage

Additional storage and backup, where high capacity is needed

Good for backups

Music and data
Data and movies
Data and HD Movies

SSD -OS drive

Flash protable data store


HarddrivesHarddrives - RAIDSolid State DrivesDisc Drives