Introducing ICT systems
Introducing ICT systems

This free course is available to start right now. Review the full course description and key learning outcomes and create an account and enrol if you want a free statement of participation.

Free course

Introducing ICT systems

13.3 Optical storage

A CD-ROM (Compact Disk Read Only Memory) uses a laser-based optical form of storage. This type of disk has been used for many years to distribute music and computer software. A CD-ROM drive is needed to read the disks. Data is locked into the disk during manufacture, and cannot afterwards be changed.

There are two other types of CD device for computers: CD-R (CD-recordable) and CD-RW (CD-rewritable). With the right sort of CD drive in your computer, you can 'burn' data (that is, write data) to either type. Data written to a CD-R disk cannot be changed afterwards, although further data can be added. Data written to a CD-RW disk can be erased and the disk reused.

CD-ROMs can store up to 800 MB of data, 90 minutes of audio or 60 minutes of video. CD-R and CD-RW disks vary in their capacity, but typically it is in the region of 700 MB.

DVD (Digital Versatile Disk) works in a similar way to CDs, but the data is held in a more compact format. In addition, DVDs can have more than one layer of data. A single data layer can hold about 4.4 GB. At the highest quality, roughly two hours of video can be held in a layer, and with reduced quality about three hours. As with CDs, there are 'R' and 'RW versions to which the user can write data. The 'Blu Ray' system, using a blue laser (instead of a red one), stores data even more compactly. This system promises to increase the capacity of a layer to 27 GB.


Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has 50 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to university level study, find out more about the types of qualifications we offer, including our entry level Access courses and Certificates.

Not ready for University study then browse over 900 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus