Eu tenho exatamente o mesmo Samsung ATIV Book 4 com exatamente o mesmo problema, e eu pude encontrar ajuda em Site da Samsung .
Most SSDs available on the market today are designed for SATA 6Gb/s
(SATA 3.x). Many consumers still have older machines, however, which
do not have support for the latest SATA revision. Fortunately, SSDs
are backwards compatible with older SATA versions. They will, however,
be limited by the maximum bandwidth supported by the host machine
(e.g. a SATA 6Gb/s SSD connected to a SATA 3Gb/s computer will not be
able to reach transfer speeds more than 300MB/s, even though the drive
might be rated for performance well over 500MB/s).
Se você é como eu, talvez esteja interessado em saber como alcançar as velocidades SATA 3. Bem, eles têm uma resposta para isso na mesma página.
SATA expansion cards are widely available in the market. These cards
promise to add and/or upgrade SATA ports on an existing system. They
are limited, however, by a certain amount of overhead and will often
not be capable of providing a modern SSD with the throughput it needs
to reach maximum performance. Thus, Samsung recommends connecting your
840 Series SSD to a native SATA 3.0 (6Gb/s) port to enjoy its full
potential.
Houve perguntas feitas aqui no SuperUser sobre isso também:
Poste quaisquer descobertas e resultados adicionais para ajudar outros usuários interessados (como eu).