I am not running SLI or crossfire but was wondering if both gpu's can continue to be used for BOINC when in SLI or crossfire mode. At one time I recall only one gpu was useable and I was wondering if that has changed recently.

This hasn't been the case since 6.6.24 for Nvidias and 6.10 for ATIs.
Since SLI and Crossfire need equal GPUs to work in SLI/XFire mode, all GPUs are recognized as "most capable".

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slightly off this topic but i have a motherboard with a x16 and a x4 slot. Can i just bung a card into the 4x slot and boinc will use it's GPU even if i don't put a monitor on it.

I forget if my board is crossfire or sli, would i need to "set it up" as in if i just bung another card in it will not automatically be in sli or crossfire mode.

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slightly off this topic but i have a motherboard with a x16 and a x4 slot. Can i just bung a card into the 4x slot and boinc will use it's GPU even if i don't put a monitor on it.

You'll have to do a few things before Boinc will see the 2nd GPU,

1st, install the drivers be it Nvidia or ATI,

2nd, Connect a Monitor, a Dummy Plug or Extend the Desktop onto the 2nd Display,

3rd, Now fire up Boinc, hopefully Boinc will now detect Both GPU's, If the GPU's are from the same Vendor, But different, Boinc will only use the most capable, so:

4th, if needed, make a cc_config.xml (using Notepad) with the following in it, drop it in your Boinc Data Directory (the location is in your startup messages, and is a hidden folder) and restart Boinc:

<cc_config>
<options>
<use_all_gpus>1</use_all_gpus>
</options>
</cc_config>

Claggy

so boinc will use 2 GPU's but only if I put that file in ? I was reading in another topic something about dummy loads not being needed anymore - have there been updates to boinc ?

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so boinc will use 2 GPU's but only if I put that file in ? I was reading in another topic something about dummy loads not being needed anymore - have there been updates to boinc ?

BOINC will use two (or more) GPUs without configuration if they are of similar specification. If the GPUs are different, it will only use the 'best' device (or devices), unless the 'lesser' devices are manually enabled.

How easily multiple devices can be seen by Windows seems to depend on both the Windows version and the device driver in use. Be prepared to experiment.