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Re: what is a framebuffer?

On Thu, Aug 09, 2001 at 12:25:11AM -0400, Faheem Mitha wrote:
> Dear People,
> This is possibly offtopic, but can someone explain to me what a
> framebuffer is, and why one should care about it? I have seen it mentioned
> quite often on this newsgroup, most often in connection with recent Matrox
> graphics cards like the g400 and g450. It appears to be something to do
> with video display.

The framebuffer is using an area of memory on your video card. it is basicaly a way to have a display on your screen, using the special features/memory of your very video card.
it is really dependant on your video card, that's why the mails you have seen were talking about matrox g400, g450, nvidia... it's a mix between a specific video card and the linux kernel.

setting your kernel/modules to use the framebuffer of your videocard will permit you to set the resolution of your screen, like 1024x768 16 million colors at 85kHz refresh ...
from there, you can use those high resolution to do what ever you want, your text console (alt-f1,f2...) can be 1200x1000 ...  you can even run a special XFree86 server on top of it (used mostly by non-x86 linux, like amiga and atari ... i dont know why, maybe they have problems with classic xfree)

in short, if you dont use text consoles much, and uses mainly Xfree, then the Framebuffer will be no use for you. because it is known that Xfree is more effeicient when using the Xfree classic server than when using the FB server. remenber Xfree server permit you to set all those resolution settings without using the FB.
the framebuffer has nothing to do with acceleration of any kind. for this stuff, tweak the Xfree server 

if you want to try, compile a kernel or modules with the FB support, install package fbset,
and cross your finger because the FB is dealing with hardware, and therefore may easily crash your system at the first false move! FB is not recommended at all for servers!
when the kernel w/ modules you run have FB support (a pinguin logo appears at boot time), you can try the utility 'fbset' to change your resolution and you can really mess up your screen!.
you will see info on the FB you are using in file /proc/fb. if it doesn't exists, you don't have a kernel that support FB.

> As far as I know, this is something I have never used, and I only just now
> seem to be hearing about it.

FB appears around kernel 2.2, and is really a revolution for some non-x86 users and 
text-mode adepts (like me). it has always been a little experimental/beta.

hope it helps

jean marc

x86 means intel-like PCs (AMD, pentiums, cyrix ...)

> The following from kernel-documentation is as much as I have been able to
> find out, but still does not convey much to me. Can anyone direct me to a
> FAQ or something that will explain this stuff (preferably in words of one
> syllable)? I'm not terribly comfortable with technical jargon.
>                          Sincerely, Faheem Mitha.
> The Frame Buffer Device
> The frame buffer device provides an abstraction for the graphics hardware.
> It represents the frame buffer of some video hardware and allows
> application software to access the graphics hardware through a
> well-defined interface, so the software doesn't need to know anything
> about the low-level (hardware register) stuff.
> The device is accessed through special device nodes, usually located in
> the /dev directory, i.e. /dev/fb*.
> -- 
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