[ILUG] Backing store (was XDM question)

[Niall]

On Wed, 1 Mar 2000, John P . Looney wrote:

> On Wed, Mar 01, 2000 at 03:24:21PM +0000, Tom Doris mentioned:
> > Whats the story with +bs (I checked the man's & couldn't find anything)?
> 
>  Backing store. It means that when a window, like "netscape" is obscured,
> the contents is saved elsewhere. So, when it's shown again, it's just a
> quick blit from video memory, instead of X telling Netscape to repaint
> itself all over again. 

Backing store doesn't necessarily have anything to do with videoram.
Having backing store available does mean what's said here i.e. that an
obscured window doesn't have to be redrawn by its application when it's no
longer obscured. However, the memory used for backing store doesn't have
to be video ram, though that would presumably be the fastest way of doing
it. I have to admit that it's donkey's years since I even thought about
backing store - I just assumed that any modern X server would
automatically use it because memory is so cheap now, compared to the early
days of X.

> Uses video ram like there is no tomorrow, but you gotta use it for
> something, no ;)

Well, presuming that the driver uses video ram for backing store. I've
never attempted to turn it on, and on this box running SuSE 6.3 with Xfree
3.3.5 it's turned on. I've just checked my cruddy old Toshiba T4900
notebook which has a 640x480 screen and all of 1M of video ram running
Mandrake 5.3 with XFree 3.3.3 - it too has backing store. I just had a
quick look at the man page for XF86_SVGA and +bs is not a mentioned
option. I'm just wondering - didn't you mention, Kate, that you're using
XFree 3.9.xx - perhaps +bs is a new switch which means to use videoram for
backing store ? Can anyone shed some more light on this ?


Regards,

Niall  O Broin

P.S. To see if you're using backing store or not, do xdpyinfo|grep option
from an xterm and you'll see.