subject: vdu console buffer question

[zhang jin]

I am reading the minix 3 text book. regarding the tty console, I understand that

the data structure, the only buffer in the console's memory is only 80 characters

long which is only a single line... but when you shift from one tty to another, the 

screen content need to be buffered and restored, so the entire win size 80x25 

chars need to be buffered, am I right?

but I just can't such buffer memory, why does it not exist? 

If it does not exist, how does select_console restore the original content?