If you want to use some of the new 2.5" SATA hard disks in your MacBook (or Mac mini for that matter), you'll notice that they do not show up in Disk Utility, and that you cannot even format them. They will work externally as a USB device, but will not show up when used internally. That's because the newer drives are SATA II (or SATA 2) and their higher "transfer rates" are not compatible with the Intel ICH7-M AHCI (which only support up to 1.5 GHz) used in the MacBook and Mac mini. To be able to use your new 250GB or even 320GB drive, you have to put a jumper on the two leftmost pins (when viewed from the front, meaning the other connector pins are on the right hand side). This worked for me on a Samsung 250GB drive, as well as a Toshiba MK3252GSX 320GB drive.

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