change the HD supplied by Apple with a SSD Crucial 256 G.
Satisfactory; the only problem (which I was able to overcome eventually) was that the thickness of the SSD crucial, compared to the supplied regular HD from Toshiba, was just about 1.5 mm more and I had a problem to keep the HD connector in place when I tried to put back on place the antenna.
Make sure to handle carefully the tape around the HD, so to be able to use it again for the HD you are going to change. Also compare the thickness of the HD you are going to swap with the installed one, because of the tightness of the space available for the HD connector to the mother board.
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