Answer (1 of 6): M1 was never used as a designation for SSD’s. The M.2 standard replaced the mSATA standard and form factor. mSATA (Mini-SATA) was a small form factor version of the 2.5″ SATA SSD’s They, like their bigger cousins, have an upper data transfer limit with SATA III of about 600 MB/s.
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