Rather than dredge up an ancient thread: upgrading an alu iMac to Penryn, I'll just create a new one. My next door neighbor's first-generation Aluminum (mid-2007) 20" iMac recently stopped working, so he took it to a local Apple-authorized service center, and got an $800 quote to fix it - dead logic board and hard drive. So he bought a new iMac. Knowing that I did computer repair for a decade, he asked if I could get the hard drive out and see about getting his data off; then muttered aloud about what to do with it (recycle, etc.) I volunteered that I'd take it off his hands to try to repair it in exchange for getting the HD out. He agreed. First thing, I tried to power it on to see what it would do. It would get to the Apple logo and spinner before just hanging, no visible kernel panic or anything. Not from the internal hard drive, not from an external hard drive, not from an OS X install DVD. Easiest thing to do was swap out RAM. So I removed both DIMMs and replaced with a known-good spare (1 GB) DIMM. Internal hard drive continued same behavior, but then it would boot from CD or external HD! PROGRESS! Booted it up, ran some tests, things appeared fine when booted from the external HD. Internal hard drive failed all checks, but I could force it to mount, and at least a few files are readable. So, next step: open 'er up, get his hard drive out, and swap in one of mine. And, since I'm ripping it open, I realized I had a 'spare' Penryn Core 2 Duo T9500 CPU lying around spare from a dead notebook. Hrm... Would this Merom-original iMac work with a later-generation Penryn processor? A quick Google search turned up this article at Hexus.net, so it looked like a go! And since I'm doing these upgrades, might as well get some memory, too. Ordered 6 GB of RAM (1-4GB, 1-2GB,) for $100, and off we go! After some effort finding a suction cup to take the glass panel off, I got it ripped open. Discovered I don't have a Torx T-6 driver, so had to leave it half-assembled as I did the surgery. Swapped out the hard drive easily enough, obviously the RAM is downright simple. Took a bit of effort to swap out the CPU though - not easy to get to! After about an hour of work, got the CPU in, and decided to plug in the minimal bits necessary to ensure it works. Left the hard drive out, didn't even screw everything back in, left it sitting on its back as I powered it up and booted from an external drive! She lives! "About this Mac" said my nominally 2.6 GHz CPU on an 800 MHz bus was running at 700 MHz on a 400 MHz bus. That doesn't seem right. The Hexus post said that they saw the same behavior, but blamed it on being an unlocked engineering-sample processor. Mine is full production, so I know that isn't it. So, I decided to do some testing. It played a 1080p video perfectly smoothly, something the stock 2.0 GHz processor had trouble with, so I know it's faster than the stock processor. Xbench showed it as being about 30% faster than the stock processor, which seems right, so I was willing to call it good, just a reporting glitch. Put the internal hard drive in, buttoned her up, and everything's great! Started out: Core 2 Duo T7300 (2.0 GHz, 4 MB L2 cache, "Merom" core.) 1 GB RAM (came with 2x 1 GB, but at least one of them was bad.) 250 GB hard drive. Radeon HD 2400 XT w/ 128 MB VRAM. Now: Core 2 Duo T9500 (2.6 GHz, 6 MB L2 cache, "Penryn" core.) 6 GB RAM (if I'm upgrading might as well upgrade all the way.) 1 TB hard drive. Radeon HD 2400 XT w/ 128 MB VRAM. (Sadly, while the GPU is upgrade-able, the Radeon HD 2600 Pro w/ 256 MB VRAM replacement MXM cards are insanely expensive on eBay.) So, for a total outlay of $100 plus two 'spare parts' I had lying around, I have a new iMac that is a good 50% faster than my previous one! (My prior desktop was the original Core 2 Duo white plastic model, 17", 2.0 GHz, 3 GB RAM tops, Radeon X1600 w/ 128 MB VRAM.) The 1 TB drive had been in use as an external drive on the white iMac as the boot drive. (I kept meaning to rip it open and put the hard drive inside, but never got around to it. Glad I didn't!) Bonus: bigger screen, more pixels, no annoying vertical lines. (My white iMac had the dreaded vertical line issue, although not nearly as bad as that one, mine only had 8 lines, spaced reasonably far apart.) So now the white iMac is being passed down to my daughter to replace her first-generation MacBook (2.0 GHz Core Duo,) which was getting a little long in the tooth (and has a dead battery.) Edit: Yes, I should have taken pictures - I was lazy, it was late at night.