Hi, I have a iMac 20" here with a Samsung 840 SSD, my neighbor told me it was very slow. On OSX 10.10 I used the application Disk Speed Test, the results were bad, 67 MB/s read, 260 MB/s write. I tried to update the firmware with the Samsung ISO on their website, I failed. The CD won't boot properly, a known issue on the internet. Thatswhy I installed Windows 7 with Bootcamp. To my surprise it told me it was on the latest firmware. I tested with Samsung Magician the speeds, it was correct now, 250 MB/s read and write. I booted up OS X again, and now the speeds are correct! 220 MB/s read and 270 MB/s write. Could somebody explain to me what happend? Thank you.