Citation Hunt

The Wikipedia snippet below is not backed by a reliable source. Can you find one?

Click I got this! to go to Wikipedia and fix the snippet, or Next! to see another one. Good luck!

In page Line code:

This text has been unreferenced on Wikipedia for a very long time. If you can't find a source, be bold and remove it!

"

Early disk drives used very simple encoding schemes, such as RLL (0,1) FM code, followed by RLL (1,3) MFM code which were widely used in hard disk drives until the mid-1980s and are still used in digital optical discs such as CD, DVD, MD, Hi-MD and Blu-ray using EFM and EFMPLus codes.[2] Higher density RLL (2,7) and RLL (1,7) codes became the de facto standards for hard disks by the early 1990s.[citation needed]