[armly]

What is the difference in SATA versions; for example SATA-300, SATA1 and SATA2?

And why don't the drives specify?

And why do some manufactures like Seagate use '3000 Mb/sec' for some of their drives and '3Gb/sec' for other of their drives?

[BG-0]

SATA 1, or SATA 1.5 GBps or SATA-150 are the same, basically. They are the early SATA drives.
SATA 2, SATA 3.0 GBps and SATA-300 are the next generation of SATA drives.

The main difference is data transfer speed.