Two 840s (TLC), one in the main bay and one in an Optibay, in a mid-2009 MacBook Pro 5,4 with the 1.7 firmware update, which allows for SATA 2 speeds: and the good news is that it negotiates at 3 Gbps in both bays, also the ex optical one; and also no beachballs, sofar: very good, indeed!
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Both SSDs required a firmware update, which worked perfectly with the downloadable ISO CD method, both from the internal optical drive and the same drive moved to the external USB enclosure included with the Optibay: so, the downloadable DOS CD updater works also from a USB connection, which is very good; rather excellent support from Samsung also for (older) Macs, thus.