External Hard Drive help ?

The only difference between SATA 1,2, and 3 is speed. They are backwards and forwards-compatible, so you can use any of them on any eSATA port.

Thunderbolt is a general-purpose high-speed connector that's basically akin to an external PCIe slot. Thunderbolt 1 and 2 are backwards and forwards-compatible with each other. Thunderbolt 3 and 4 are backwards and forwards-compatible with each other. You need an adapter to use Thunderbolt 1/2 device on a Thunderbolt 3/4 port.

In all of these cases, you need to make sure your computer actually has these ports to use them. Thunderbolt is usually only found on higher-end computers.

internet search will get explanations

SATA I, II & III (roman numerals) are not connection types, but standards revisions. they all use the same connections for data and power, but each is held to a higher standard than the previous revision.

SATA III can transmit up to 6Gbps, and has an interface throughput of about 600MB/s.

i should point out that none of these SATA standards is used for external drives, at least, not to connect them to the computer.

usually, USB is used, or Thunderbolt on a Mac computer.

the SATA connection is used on the hard drives themselves, on the inside of the external drives. these drives are the very same drives used inside computers, just in an enclosure instead of inside the computer. then the USB or Thunderbolt cable connects the enclosure to the computer.

anything else you wanted to know?