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| <H2><A NAME="s3">3. Console generalities</A></H2> |
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| <!-- |
| console!theory of operation |
| --> |
| <P>Conversely, when you output something to the console, it first undergoes |
| the standard tty processing, and then is fed to the console driver. |
| The console driver emulates a VT100, and parses the input in order to |
| recognize VT100 escape sequences (for cursor movement, clear screen, etc.). |
| The characters that are not part of an escape sequence are first converted |
| into Unicode, using one of four mapping tables if the console was not |
| in UTF-8 mode to start with, then looked up in the table describing |
| the correspondence between Unicode values and font positions, |
| and the obtained 8- or 9-bit font indices are then written to video memory, |
| where they cause the display of character shapes found in the video card's |
| character ROM. |
| One can load one's own fonts into character ROM using <CODE>setfont</CODE>. |
| The obsolete programs <CODE>loadunimap</CODE> and <CODE>mapscrn</CODE> can be used |
| to manipulate the Unicode map belonging to the font, or the mapping |
| table of the console. More details will be given below. |
| <P>There are many consoles (called <I>Virtual Consoles</I> or |
| <I>Virtual Terminals</I>, abbreviated VCs or VTs) that share the same |
| screen. You can use them as independent devices, either to run |
| indendent login sessions, or just to send some output to, perhaps |
| from <CODE>top</CODE>, or the tail of the system log or so. |
| See below (`Console switching') on how to set them up and |
| switch between them. |
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