Named Instance timeout problem

I am running two large applications on a 4 cpu SQL server with 2 named instances.
There are times when I am running a query on one named instance that users on the other instance are getting time out errors. I am trying to justify giving each instance limits on which cpu's they can use and also potentially memory. I tried giving the
more critical application 3 cpu's and the other one cpu. There was still a similar problem on the critical app when running a intensive query on the other which was just allocated one cpu. My boss insisted that I change both back to sharing all cpu's.
My argument is that if both can hog all 4 cpu's, I can guarantee that there will be a problem.
When the large queries are running, the HD lights are on constant and the CPU's are all pegged at 100%. The databases for each application are stored on their own mirrored HD.
I was wondering if anyone out there has experienced a similar problem and wondering where to go from here.
Thank You,
Everett
We went with defaults when the instance was installed. I think both are
dynamic.
"Vikram Jayaram [MS]" wrote:

> What about memory allocation? Are both instnaces alloted to have Dynamic
> Memory? In that case one instnace could be hogging system memory and not
> granting the other enough, on time.
> Vikram Jayaram
> Microsoft, SQL Server
> This posting is provided "AS IS" with no warranties, and confers no rights.
> Subscribe to MSDN & use http://msdn.microsoft.com/newsgroups.
>
>
|||Right then., Try alloting one of those to fixed memory of a lesser amount
and see if the behaviour still exists. Worth a try!
Vikram Jayaram
Microsoft, SQL Server
This posting is provided "AS IS" with no warranties, and confers no rights.
Subscribe to MSDN & use http://msdn.microsoft.com/newsgroups.