Who is affected
The following is confirmed by me  [ in Win 7 X64 RC ]  and by a colleague of mine who is a MSDN subscriber who has access to the final / RTM Windows 7 X64.    It is NOT  a Sonar 8.5.1 issue - it is an O/S issue.   It is also NOT  present in Vista SP1  x64 or X32.   It  only  applies to Windows 7 X64 and X32 and  only  in systems using  more  than 2 physicial CPU's  and/or  more than 2  "logical" cores - ie:  Core i7 DAW's.

The Problem

Core Parking is VERY bad for DAW's - great for  non-DAW Laptops - but very bad for us in the DAW world.

See here for a bit of info / explanation / more info about CPU Core Parking - http://channel9.msdn.com/forums/Coffeeh … n-4-cores/
Without the following  " fix "  you will see massive CPU spiking in Sonar and Windows Task Manager - some CPU cores will be "turned off" / "parked" depending on load and they will be dynamically turned on or off and dynamically loaded up or down as the system deems necessary -  the scope for glitchs / pops / clicks / droputs  etc.... in such an environment is simply enormous.
To the best of my knowledge, there is no known "switch" to turn it off - no utility I am aware of to "tweak" it off.

The Fix

- go to REGEDIT
- Search and Find this key  [  54533251-82be-4824-96c1-47b60b740d00  ]  without the   "  [  ]  "
- alternately, you can search and find the phrase  "  Core Parking "  -  again without the  "  "
- either of the above searchs works and delivers the exact same results
- delete the key(s)
- make sure you search the whole Registry - you should find it  [ from memory ]  6  times but will only be able to delete  [ from memory ]  the first  2 or 3 instances - dont worry about the ones you cant delete - just delete all the ones you can
- exit the Registy
- Shutdown Win7
- Do a full cold shutdown and re-boot

The Result

Perfect* load balancing across all you CPU cores - no spiking - both in Windows 7 Task Manager and Sonars CPU meters

Hope the above is of help.

Tom

* -  you will still see some  " unevenness "  depending on the EFX / VST / Synths  etc... you use because unlike Sonar - which is excellently "coded" to be multi-thread aware, compliant and cpu-load-balanced,  many, many other  EFX's / VST's / Synth's  etc...   [ most actually ]    are very lazily and poorly coded / written and  are no-where near  as  " even "  when it comes to multi-thread awareness,  compliance and cpu-load-balancing.
<message edited by TomG on November 01, 09 5:28 AM>