Optical Storage

Optical storage uses a laser to read data from a disc. The three common optical media are CDs, DVDs and Blu-ray discs. A Blu-ray disc generally holds more than a DVD, and a DVD generally holds more than a CD.

An optical drive reads a disc, and some drives can also write to it. Not every disc can be written: a read-only disc (ROM, such as a CD-ROM) is fixed when it is made and can only be read, an R disc (such as a DVD-R) can be written once and then only read, and an RW disc (such as a DVD-RW) can be rewritten many times. For example, a read-only disc might hold the finished video of a school show, while an RW disc could be reused for each year's rehearsals.

Weaknesses

Optical storage has a low capacity and is slow next to magnetic and solid state storage. A disc holds far less than a hard disk or SSD, and reading or writing data takes longer. A disc is thin and light, which makes it easy to carry and post, but it only works in an optical drive, and many modern computers no longer have one.

Discs are also fragile. They are easily scratched, cracked or snapped, and because the laser reads the surface, a scratch can make part of the data unreadable. They can degrade over time too, especially if they are stored badly, such as in a hot, sunny or damp place.

Where discs are useful

Optical discs are inexpensive to buy, and making them in large batches keeps the price low. That makes them a practical way to hand out copies of media, such as a museum giving visitors an audio guide on CD, and for small backups or archives, such as a family keeping a copy of old photographs on a disc in a drawer. They are less suitable for everyday work where you need lots of space and quick access.