EDT makes it possible to process texts present in different character sets. The method of operation in compatibility mode is very different from in Unicode mode. Since EDT never converts data from one character set to another in compatibility mode only limited support is available in this mode.
In compatibility mode, EDT always has precisely one defined character set.
Texts can therefore only be processed simultaneously if they are present in the same character set. This character set can only be modified if no data is present in the work files. It is therefore defined when data enters a work file. EDT also uses this character set to communicate with the terminal or to read and write its input/output when communicating with other sources. In particular, EDT can only process files if it is guaranteed that these can be fully displayed on screen. Certain character sets are therefore excluded, for example EDF03DRV, EDF046 and ISO character sets.