Frame buffers are nothing more than memory regions that are used for graphics.

Modern graphics cards have kernel-native drivers which are used for KMS (kernel mode setting) and can use very high-resolution and high-speed framebuffers even on dual heads.

However, the card emulated by QEMU there does not have such a driver. You’d have to be emulating one of the major supported chipsets in order to get such a thing; otherwise, all you get is the old-style VESA framebuffer, which is very slow though still higher-resolution than 80x25 VGA text mode.

See [Wikipedia’s “Framebuffer” article][0] for more information than you’d really ever want or need on them. Also, see [this article from Phoronix on KMS with QEMU][1], but I don’t know what the current status of it is and it appears to depend on QEMU-KVM and not stock QEMU itself.

[0]:http://en.wikipedia.org/wiki/Framebuffer
[1]:http://www.phoronix.com/scan.php?page=news_item&px=OTM0Nw