[ubuntu-uk] Screen resolution problems on dual-monitor setup

Liam Proven lproven at gmail.com
Thu Aug 11 18:37:24 UTC 2011

On 10 August 2011 18:41, Jim Price <d1version at hotmail.com> wrote:
> I think something is up with the attributions here - thunderbird and gmane
> are telling me this post is from Liam, but I think it may have been said by
> some combination of Liam and James, or just James:

Odd. You replied a bit to both of us. :¬)

> The next bit sounds like it might be attributable to Liam? Or not?
>> Aha! That is interesting.
>> I will say that on my old Thinkpad, to use multiple monitors at all, I
>> have to drop all the screens down to 16-bit colour.
>> (Either 65,535 or 32,768 colours, it makes no real difference. Most
>> "16-bit colour" modes are actually 15-bit colour: 5 bits for R, G&
>> B.)
>> On Windows I have to do this manually, by setting both screens,
>> individually, to 32K colours - *then* changing resolutions. The
>> Thinkpad only has 16MB of video RAM, which limits it to 2 screens at
>> 1024*768 in 24-bit colour. In  16-bit colour, I can run 1024*768 +
>> 1280*1024. On Ubuntu, there is no UI for changing colour depth, so I
>> use the xorg.conf file I documented in my blog.
>> You might want to try this if your machine is of a similar age.

Yes, that was me.

> I'm thinking checking the amount of memory allocated to the graphics in the
> BIOS might be worth doing. For X to have enough memory for both displays at
> 32bit colour, you would need ~75MB, although the settings are likely to be
> in power-of-two increments, so you might need to set it to 128MB shared
> memory as the next highest setting.

FWIW, on my Thinkpad, you can't - it has 16MB of physical VRAM and
that's it. The symptom of VRAM starvation, just for the record, is
that the dialogs /show/ higher resolutions (e.g. 1024*768 + 1280*1024)
but if you try to select the higher ones, you actually get a lower
one, such as 2 x 1024*768.

>> There are no proprietary ATI drivers for my "Mobility Radeon" chipset
>> - it's too old.
> That's what I suspected.
> Can you tell us what model of laptop you have there, so I can google for the
> graphics configuration it supports?

That was me, but FWIW, it's an IBM Thinkpad X31.

Liam Proven • Info & profile: http://www.google.com/profiles/lproven
Email: lproven at cix.co.uk • GMail/GoogleTalk/Orkut: lproven at gmail.com
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