Apple may have switched to a slower SATA interface with some new MacBook Pros.
Apple had used SATA II for its MacBooks but appears to have reverted to the older and slower SATA I for some new MacBooks. The affected models are the 13in and 15in screen MacBook Pros. The 13in white MacBook and MacBook Air and the 17in MacBook Pros use the SATA II interface.
A thread on the MacRumours web forum provides more information, including the suggestion that a firmware upgrade could fix the problem. Apple has not responded yet.
The Serial ATA interconnect links computers with disk drives and ran at 1.5Gb/s in its first incarnation, That was upgraded to 3Gb/s in the second generation of the standard, and the latest SATA III version operates at 6Gb/s.
The SATA degrade shouldn't affect hard disk drive MacBook users, but may well affect users with Flash-based solid-state drives (SSDs). Benchmarks indicate slower SSD I/O than with the 3Gb/s link, with large sequential reads the most affected. Overall, SSD use in the affected MacBooks should still show faster performance than with hard disk drives. ®