"upgraded" cpu from athlon 3500 to 3800 X2. Machine slowed down!?

You might try downloading AMD's dual core optomizer and latest 9/2007 processor driver.

http://www.amd.com/us-en/Processor [...] 06,00.html

How about, did you adjust the settings like the cpu voltage?

First, check to make sure that you have both cores displaying in your task manager. If you do, you are fine. If you don't, then we have other issues to sort out. Second, check that you have 2 cpus showing in your device manager.

YOU DO NOT NEED TO REINSTALL WINDOWS FOR A DROP IN CPU UPGRADE from a single to a dual core. This is a very, very last resort.

All that aside, here is what happened and I try to let people know this every chance I get. You went from a 2.2 ghz single core processor to a 2 ghz dual core. The dual core for raw speed you upgraded to is SLOWER than the 3500+ you had. The difference is with the dual core you will be able to multitask better when the CPU has the chance to use both cores. Your games should run a little smoother, as some of the background processes in Windows will be handled by 1 core while the other core powers your game. But for benchmarks and pure max frames per second, you needed to upgrade to a dual core that is at least the same ghz as what you had, preferably faster.
The only concellation is that you should be able to overclock your dual core to at least 2.2, and maybe even 2.4 ghz quite easily with the stock cooler. Then you will see the benchmarked improvement, and you will notice an overall improvement in your gameplay.
If you are playing a game that is mulithreaded, (like Crysis) you should see a significant improvement with your dual core even at the stock speed.

With all due respect to jitpublisher, reinstalling Windows is often the only solution that will work. Just last month I went from a FX55 single core to dual core X2 4200, and I tried everything for almost a week. (installing Core Optomizer, resetting abstract layer, installing and reinstalling BIOS, tinkering with BIOS, etc.), yet nothing I did would get it to "recognize" both cores.

Someone advised that I reinstall Windows, and low and behold that did it. They key is Task Manager. You should see TWO individual graphs for processor use. Regardless of whether your system ID says "Dual Core", regardless of whether your device manager says dual core, regardless of whether the system correctly identifies and names the processor, it all comes down to whether Task Managers shows two active processors in two distinct graphs.

Otherwise, jitpublisher is right on the money as to performance: I can't say things are sped up per se, but everything is smoother. The average completion time for a task is about the same, but whereas about 1/4 of the time there might be some system hangup, now there are never any hangups.

I did some mild over clocking from 2.2 to 2.4, and even with a 2 year old video card, I can run Crysis on medium to high (for what that's worth).

Good luck!

I felt compelled to answer.

First of all the AMD Athlon64 X2 3800+ is clocked at 2GHz (each core respectively). Your AMD Athlon64 3500+ is clocked at 2.2GHz.

Therefore when running single threaded applications (like most of the Passmark tests) you will see a decline in performance.

It's only logical.