Braille is a writing system that maps characters to rectangular blocks of dots (three dots high by two dots wide) called "cells." In Grade 1 Braille, each character is represented by one cell. In Grade 2 Braille, which is more advanced, hundreds of common abbreviations and contractions are added. Grade 2 Braille is most commonly used in publications, and is generally what is meant by the phrase "English Braille." Grade 3 Braille refers to personal shorthands that a Braille user might develop, and is almost never used in publications. These patterns of dots can be printed as embossed bumps on a page, and a blind individual can read them with their sense of touch. Pages of embossed Braille text can be produced using Braille typewriters or by using embossing printers.
Refreshable Braille displays are electro-mechanical devices that include the ability to generate raised bumps dynamically. Commercially available Braille displays can generally display one line of between 12 and 80 cells at a time. In some models, vibration is used on particular cells to indicate the location of a cursor in the text. Prototypes for multi-line Braille displays have been developed, but no multi-line Braille displays are commercially available at this time.
Refreshable Braille displays may be the most popular option among professional programmers and others who need to closely proofread their work. However, they are quite expensive and screen reader software or printed Braille are more commonly used. Part of the reason for this is that only 13% of individuals with impairments (including all types of impairments, not just vision impairments) are aware of Braille embossers and printers, and only 8% are aware of refreshable Braille displays (see Accessible Technology in Computing - Examining Awareness, Use, and Future Potential, a study Commissioned by Microsoft, Conducted by Forrester Research, Inc. in 2004). In addition, only 10% of blind school children are taught Braille, even though 80% of all employed blind people read and write Braille fluently.