On 10/04/2018 14:09, whisky-dave wrote:
Years ago, well the early 2000s I heard that some buses would only run at the speed of the slowest device, so if you had a CD/DVD drive in the same chain (IDE) then you're HDs would run at the same speed as the CD drive so not very fast.

That's not why an SSD is faster.

With a conventional spinning rust disk to read something off the disk
you have to
1 Send it a command
2 Have it work out what you mean
3 Move the heads across the disk to the right track (like selecting a
track on an LP)
4 Wait for the disk to go around to the right position
5 read the data off the disk
6 transfer the disk to the PC.

The old PATA CD slowdown thing affected #6 only.

On a spinning rust disc 3 & 4 will both take several milliseconds, and
are the slowest part of the whole process.

On an SSD steps 3 & 4 are missing from the sequence.

SSDs _do_ have one problem spinning rust discs don't, but you rarely see
it - if you write a _LOT_ of data they can run out of spare blank space
to write to, and they have to slow down while they clean a bit more. The
trim command (hi John!) is designed to let it know about free space it
can erase in advance.

Andy