Originally Posted by
Embers
There is no extra "processing" in an external drive,
why most old external drives are usually slower is due to the bottleneck of the connection interface, for example, if you were using a USB 2.0 connection to your drive it will be giving you max speeds of 480mpps at max. Whereas USB 3 supports 5gbps, 3.1 supports 10gbps and thunderbolt 3 a whopping 40gbps.
These transfer rates are faster than even the most high-end PCIe SSD's out there, so the bottleneck now would be either the drives speed or the electronic interface between the drive and the cable which is relatively small about 10%.
So, in a nutshell, an external drive will be almost just as fast as an internal one, given that it is not made by some cheap company that cheaped out on the interface.