Hi, Anyone got any experience of an iMac throwing "kernel: disk0s2: I/O error." errors even after the internal drive has been replaced? Could it be the SATA cable or logic board or perhaps just some errant software? I have a 2007 Aluminium iMac which I've owned since new. I upgraded the hard drive from 320GB to 1TB 2 years ago and it has been running faultlessly for nearly 5 years. I've been running Mountain Lion since the first previews were released and it's been pretty good with only a few little glitches here and there. A few days ago the machine started running really badly with lock ups and beach balls etc and a quick look in the log files showed "kernel: disk0s2: I/O error." messages scattered around. I made the reasonable assumption that my disk was failing and sourced a new one and fitted it. I restored from Time Machine, going back to before the machine became unstable to avoid any corrupted files. The TM restore took ages and the result was that the disk I/O errors were still showing up and the machine was still hanging. I decided to do a fresh install so downloaded the newly released GM seed of ML and tried to install that but the downloaded DMG file could not be verified prior to install, suggesting corruption during download. Sure enough there were a few disk I/O errors in the log files during the download. I ended up doing the Cmd+R recovery HD thingy and installed ML from Apple's servers directly. It took a while but worked. Note that this was a fresh install over the top of the existing TM restore so is probably more correctly called an upgrade but if I understand correctly, this does replace the System folder and kernel etc. Now the machine has been a lot more stable but just now I tried to download the XCode 4.4 GM Seed from Apple and it has become corrupted during download with some more disk I/O errors in the logs. I should mention that I removed VMWare Fusion and some other bits of software which do low-level hardware manipulation and I've upgraded as many applications as possible to try to make sure everything is supported by ML but clearly I still have a problem. My previous drive was getting very full (about 85%) and I know that Macs don't like full drives but I doubt that is the issue. So, what's my next step? Replace the SATA cable? It felt very positively engaged when I replaced the hard drive but I have heard of at least one report of someone having a bad SATA cable on a MBPro. Maybe a clean install onto a freshly formatted drive while waiting on a cable arriving? Any ideas would be very welcome - most of the advice on the web just says that the drive is dying and to get a new one but I've already done that. By the way, the old drive is now in an enclosure and I still see disk I/O errors when accessing it via USB which either means it is detecting errors caused during a failed write operation or this issue doesn't just affect the SATA interface which may point to software or logic board. Yes the new hard drive could be faulty but it seems unlikely that I would see the exact same issue. Oh, one other thing to mention - I've already done the Apple Hardware Tests (both short and extended tests) and they came up clean. Thanks, Craig.