I own one of these and am on it now: I had a real fun learning about it and upgrading it in several ways.....the eMachine BIOS suggested a whole slew of processors compitable and I went from the Celly 356 to Core2Duo E4600 flawlessly and very straight forward. I later opted for the C2D E6700,(also installed effortlessly)as it has a much larger L-2 cache/faster FSB, although not that of a speed bump in actual GHz. In addition, after the stock hard drive went south,I opted for a 500GB SATA w/32mbs cache...was a nice bump. Also, while the mixed info suggested 2GBs max on RAM, I am using 3GBs---Intel sez 4GB is max on 32bit Vista, but in that 32-bit conundrum,all of it wouldn't be seen. The rig is happy w/3!
While the on-board video is just passable(NOT FOR GAMING/PHOTO-VID EDITING), I have upgraded to 2 different nVidia graphics card...the first was a 8600GT (OC) by BFG and the second one was a 220GT from PNY. The reason for stopping there was concern over bottlenecking in the PCI channels (PCIex16 v1.1 for this motherboard), and found the 8600 to be a real power hog, despite bumping up the Power Supply to 425w, from the 300w stock. The second upgrade got all the power issues better ironed out with the much smaller GPU on that card---but it's not a quality card. It suffices for my purposes,however.
The BIOS is inflexible as far as voltages and really, timings for the RAM. It's an Intel thing for the 945 chipset and better board can now be had that's more flexible in overclocking/tweaking regards: this is the 2007 offering from Intel,however, and you could be better served by the other suggested ones , if you desired OC features.
The D945GCL .pdf suggests that the cpu can be any Celeron,Pentium, Core2Duo Socket 775 cpu that is 533/800/1066 mhz FSB--
• Intel Core 2 Duo processor in an LGA775 socket with a 1066 or 800 MHz
system bus
• Intel Pentium D processor in an LGA775 processor socket with an 800 or 533 MHz
system bus
• Intel Pentium 4 processor in an LGA775 processor socket with an 800 or 533 MHz
system bus
• Intel Celeron D processor in an LGA775 processor socket with a 533 MHz system bus
-but the BIOS was written before quad core cpus and performance boosts/features on the top end of the dual cores.I don't think the x6800 C2Duo would work,as that BIOS was written well after the ONLY one eMachines had in this mobo at the time. So I stopped at the 1066 FSB/4mbs L-2 cache/2.67GHz E6700 Core2Duo. I was confident that if I installed a cpu that fell within the same revision of BIOS compatibility as the Celeron 356, it would fly----and it did . Right out of the box! Your results might differ, but my experience was the simplest, easiest upgrade I've ever done. Hope this helps you somewhat.
I also meant to add that the Windows Experience rating (for what it's worth) went from 3.-something to 5.3....sufficient for what I use the PC for!