[DannyBee]

To give you an example, these are often used in CNC machines.

Before you had to have:

A. a PLC that ran logic with real time guarantees to tie everything together. The PLC is often user-modified to add more logic.

B. Decoders that processed several mhz encoder feedback signals, somewhere between 3 and 10 of these.

C. Something that decides what to do with the data in B

D. Encoders and motor driving, also being output at several mhz (somewhere between 3 and 10 of these as well)

Among other tasks.

These were all separate chips/boards/things that you tried to synchronize/manage. Latency could be high. But if you are moving 1200 inches per minute (easy), 100 milliseconds latency is equivalent to losing track of things for 2 inches. Enough to ruin anything being made.

Nowadays it is often just an FPGA hooked up to a host core.

(or at a minimum, a time-synchronized bus like ethercat)