Just reporting back that I installed a Samsung 850 Evo SSD 250gb in my mid 2009 macbook (non-unibody, non-Pro), and all seems fine. Runs Yosemite like greased lightning etc. Did a clean install from scratch, no data transferred. More info: THE GEAR Mid-2009 non-unibody macbook. 4GB ram, 500GB spinny hdd, running OSX 10.10 Mavericks Seemed weird to be 'downgrading' from a 4-year old 500GB to a shiny new 250GB but that's the way it is. Samsung 850 Evo SSD purchased from the Amazon, £80 Also purchased a SSD-specific enclosure for 1) doing some work with the SSD before installing it, 2) putting the SSD in in case the installation didn't work, 3) putting the old 500GB hdd in, and 4) in a year or so, will put the SSD back in the enclosure when /if the Macbook is finally decommissioned. Brought this one: Inateck 2.5 Inch USB 3.0 Hard Drive Disk HDD External Enclosure, Optimized For SSD, Support UASP SATA III, £16 http://www.amazon.co.uk/Optimized-Inateck-Enclosure-Installation-Compatible/dp/B00FCLG65U The Inateck Enclosure worked really well. Testing the enclosure with the Samsung SSD inside with my 2013 Macbook Air gave me around 400MB-500MB/s over the USB 3.0 port - the fastest I've ever seen an external drive. Of course, testing it with the 2009 Macbook over USB 2.0 brought it down to about 20-30MB/s. Transferring the 8GB Yosemite installer file from the MBA to the external took about 12 secs , and from the external to the '09 MB took well over an hour Inateck enclosure is a bit thicker than I would have liked, as it can take 9mm HDDs, which I haven't seen in a long time, but I will take a couple mm extra in return for blazing speed. THE INSTALL Transferred the OSX Yosemite installer from the MBA to the MB, as above. I should have downloaded it on the MB, but the Air has faster download, and I fancied testing the enclosure transfer rate. Opened up the MB, whipped out the HDD, put it in the enclosure. Time taken: roughly 3 minutes. (plus an extra 20 mins to find a hex Allen key to fit the tiny bolts on the HDD tray in the MB. Another two minutes to put the SSD in the MB and close it up. Connected the enclosure to the MB, started it up. MB automatically booted from the USB enclosure into OSX Mavericks, no need to hold down any key. Ran Disk Utility, formatted the SSD, standard format, didn't bother with partitions. Ran the Yosemite installer, double checked which drive it would install on, checked again, and released it at the SSD. Took about 20-30 mins I think. Refused icloud, online services etc (they slowed down the MB when it was running Mavericks). Refused to transfer data from the old HDD. (I want a completely clean install). A few minutes later, Yosemite latest version was up and running on the MB. Yay. THE AFTERMATH Installed MS Office etc, which probably took longer to run through all its updates than installing Yosemite. In the MB, the SSD is giving about 200-250MB/s, much faster than the old HDD. Apps etc open instantly which is lovely. I haven't bothered with activating TRIM etc. What I'm reading is confusing, also I want this to be a low maintenance computer. Am trying to install as little extra software as possible and turn off as many OSX system services as possible (ie no iCloud, no PhotoStream, no Handover, untick unwanted categories in Spotlight prefs etc) to keep up the system speed. So far, all seems fine. THE PUZZLERS Two things puzzled me: - The MB auto-connected to my bluetooth Apple keyboard, which I had been using with my Air, leading to a bit of headscratching for a moment. This was with a brand new SDD, new install of Yosemite, no data transferred, the keyboard hadn't been paired with the MB, so how did the MB pick up on the keyboard, and how did it know the name I'd given to the keyboard? (The MB was paired before, when running Mavericks on the spinny, but all that info should be gone) - Spotlight search insists on showing me any file which has my search string in the coding - .html, .xml, all the 'Developer' files, and I can't turn this off. Grr.