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Jun. 21st, 2010 04:33 pmI have a rather elderly notebook, an IBM Thinkpad X31, that's rather quicker under Linux than in Windows these days. One of its few drawbacks is that it only has 16MB of video RAM on a fairly crappy old ATI Radeon Mobility chip. Still, it does support multihead. The snag is, it doesn't have enough VRAM to drive two displays at more than 1024×768 in 24-bit colour. Try to set an external display to 1152×864 or 1280×1024 while in truecolour mode and things go badly pearshaped fast.
Snag 2: Ubuntu and Mint don't offer a UI for changing colour depth any more. I guess the developers just assume everyone's machine is modern enough to run in 24-bit mode all the time, which probably any machine less than a few years old will. Mine's six years old and it's not up to it.
If you go searching for info on switching to 16-bit colour, though, you find lots of info about adding lines to /etc/X11/xorg.conf to restrict the colour depth. The snag is, I don't have one; these days, x.org doesn't seem to bother creating one if it can autodetect your graphics controller.
There are also some lengthy pages on how to write one from scratch, extracting info from your running system to build the correct file. That seemed like a lot of unnecessary work to me - after all, the X server is already working.
So I was rather happy to come across this page, which give a sort of blank default xorg.conf file that makes no specific reference to what chipset or monitor you've got.
All you need to do is create an empty file, paste this in, amend the settings as desired, save it and restart.
In there, you can enter a list of video modes if Ubuntu isn't picking up the right ones - such as widescreen modes. You can set a preferred colour depth - in my case, 16-bit.
Log out and back in again and suddenly I can run the internal screen at 1024×768 and an external LCD at 1280×1024 simultaneously, and not only does it work, it's dramatically faster at scrolling and window-dragging than in 24-bit colour, too.
Works fine on Mint 9, too, for what it's worth.
Snag 2: Ubuntu and Mint don't offer a UI for changing colour depth any more. I guess the developers just assume everyone's machine is modern enough to run in 24-bit mode all the time, which probably any machine less than a few years old will. Mine's six years old and it's not up to it.
If you go searching for info on switching to 16-bit colour, though, you find lots of info about adding lines to /etc/X11/xorg.conf to restrict the colour depth. The snag is, I don't have one; these days, x.org doesn't seem to bother creating one if it can autodetect your graphics controller.
There are also some lengthy pages on how to write one from scratch, extracting info from your running system to build the correct file. That seemed like a lot of unnecessary work to me - after all, the X server is already working.
So I was rather happy to come across this page, which give a sort of blank default xorg.conf file that makes no specific reference to what chipset or monitor you've got.
All you need to do is create an empty file, paste this in, amend the settings as desired, save it and restart.
Section "Device"
Identifier "Configured Video Device"
EndSection
Section "Monitor"
Identifier "Configured Monitor"
EndSection
Section "Screen"
Identifier "Default Screen"
Monitor "Configured Monitor"
Device "Configured Video Device"
DefaultDepth 16
Subsection "Display"
Viewport 0 0
Depth 16
Modes "1280x1024" "1024x768" "800x600"
EndSubSection
EndSection
In there, you can enter a list of video modes if Ubuntu isn't picking up the right ones - such as widescreen modes. You can set a preferred colour depth - in my case, 16-bit.
Log out and back in again and suddenly I can run the internal screen at 1024×768 and an external LCD at 1280×1024 simultaneously, and not only does it work, it's dramatically faster at scrolling and window-dragging than in 24-bit colour, too.
Works fine on Mint 9, too, for what it's worth.
