Re: vc scrollback

Ricky Beam (
Fri, 13 Oct 1995 13:36:07 -0400 (EDT)

>> On Sun, 8 Oct 1995, Axel Boldt wrote:
>> > I believe the whole vc system is fundamentally flawed. It is not the
>> > kernel's business to do console scrolling or console switching. That's
>> > to be done by a user process, namely by screen, available from all GNU
>> > sites. It multiplexes a character terminal, giving you all the
>On Mon, 9 Oct 1995, Joe Fouche wrote:
>> ABSOLUTELY. Great idea. The more mature Linux gets, the more we (he? :)
>> should filter out things that were really put in there to make
>> development nicer, etc. It saves memory, etc.
>I think having an separate scrollback buffer for each vc would be nice,
>but as Axel already said, it's easyer to simpy use screen.
>If this is added, IMHO, a few config options could be nice then:
>1.) As Axel sayed, I think an config option for disabling vc switching and
> vc scrollback.
>2.) If it's feasible: vc switching without scollback
>3.) The current state of art.
>4.) Full vc switching and scrollback
>5.) A changeable Limit how many lines are remembered.
>Compilcated task doning that all, likely resulting in more questions about
>this, so I don't request it all.
>As I'm not a console developer, others likely may know better. :-)

Anyone who cares to look at the code and understand the hardware will want
to kill you for that list...

1> Disabling the VC's is simple, but that may break several applications
like X.
2> VC switching already kills the scrollback.
4> Full scrollback for every VC is not that much of a problem, you just
lose 32K per screen for the kernel to swap out the active frame buffer.
5> The limit on how many lines is controlled by the HARDWARE limit of 32K.
If you screen only uses 512bytes then you get a good bit of scrollback. But
with a 16K screen, you only have 1 screens worth of scrollback. Trying to
make that bigger will only increase the load on the kernel to do what screen
does -- a software scroll. By default the kernel is using the hardware
scrolling ability of the card to scroll the screen without having to copy
everything on the screen minus one line. Granted most accel. graphix cards
have functions to do block copies and all that jazz.


Disclaimer: I am by no means an expert in this matter, so take this with
a grain of salt.