Hi there!I'm replacing my Intel Core 2 Duo (E4500) with Intel Core 2 Quad (Q6600), Intel MoBo DP35DP. My OS is Windows XP Home SP2. The system sees only 1 core (Core0). I'm not an expert in hardware, so once I did a research on the topic, I got quite confused. Some people say I need Windows XP Pro to enable 3 other cores, while others say quad cores should work just fine with Home Edition. My understanding now is that I can't use multiple *processors* with Home Ed and I need to go with Pro. But Core 2 is a *single* processor with 4 cores! Am I missing something?I upgraded BIOS, got every OS update but SP3, ... still, only 1 CPU is seen in Task Manager, SpeedFan, and CPU-Z. On the box, it says that this MoBo/CPU compo is compatible with XP Home, so I assume it should use all 4 cores! I really appreciate any help with that as I have no means of trying to make it work with XP Pro without actually buying it. Thanks!P.S.: Sorry if this had been asked here before but I couldn't find anything relevant by searching.

I don't think home/pro has anything to do with your problem. Did you do a clean OS install on the new hardware? I think maybe you need to have a different HAL for ACPI multi-core. Once the HAL is created during initial system install, it isn't changed, except by doing a power-tweak. But I'm just guessing, don't really know for sure.scott s..

Yes, it's the HAL.You need to reinstall Windows XP.It doesn't matter if it's Home or Pro.

I did reinstall XP with BIOS reset - same thing. By the way, SpeedFan now shows 2 cores (Core0 and Core1), whereas CPU-Z shows 1 core/ 1 thread. Intel PIU shows 4 cores. (attached screengrab) What is a definitive way to know how many cores are enabled?http://i282.photobucket.com/albums/kk264/g..._q6600_diag.jpg=S.V.=

It's all fixed now, thanks to http://www.notebookforums.com/thread183802.htmlI'll repost here, as I lost sleep over this thing in the last 2 weeks, so if anyone has same issue, try this! It worked for me. I repost only 1 method that I used:-------------------You can do this two ways.Option #1 - Hal / NToskrnl replacementa. Make a directory called DUO on C:b. Copy halmacpi.dll (search your C: drive for this) to C:DUO then rename it to hal.dllc. Copy ntkrnlmp.exe (search your C: drive for this) to C:DUO then rename it to ntoskrnl.exed. Make a batch file called go2core.cmd and put this in the file.C:CDwindowssystem32REN hal.dll hal.oldcopy C:Duohal.dll C:windowssystem32REN ntoskrnl.exe ntoskrnl.oldcopy C:Duontoskrnl.exe c:windowssystem32e. Run Go2Core.cmd from C:duo directory.f. Reboot and you should now see two processors in Task manager-------------------After reboot log in in a safe mode, it will install missing parts, reboot and here you go:http://i282.photobucket.com/albums/kk264/g..._diag_fixed.jpg=S.V.=