FPGA is an actual hardware implementation. The gates in the FPGA really do reconfigure themselves to be a certain CPU, video chip, etc.
example
real chip
5 * 5 = 25
FPGA
5 * 5 = 25
emulation
? = 25 ( we now have to guess on a very fast CPU with lots of ram how this was worked out in real time and with trial and error see what works with a lot of custom code ) 1*25 , 1+24 , 28 - 3 , and SO on until that part of the code starts to work.
then there is the order of the code
FPGA behaves Exactly like real hardware everything runs as it should to an exact cycle in the order it was meant to, also at the correct speed, no 3ghz i5 with 4gb of ram required to emulate a cycle accurate z80 cpu but on fpga the z80 runs at 1mhz in the same space required by the real chip with the same logic and gates so its a copy and not being emulated by a complex set of instructions , lookup tables, there are NO cpu or programming preset in fpga just the layout of a z80 , 68000 , ymsound chip aga chipset etc when layout is done..
but as with emulation as in the Billy Mitchell case , it was proved he used mame emulation due how mame incorrectly draws the screen tiles. not as in real hardware as does Mist FPGA correctly draws the screen exactly like real hardware.
in fact a different rom runs fine on the DK hardware because the FPGA layout is a hardware reproduction 1 to 1 of the real chips. nothing is emulated just copied / cloned.
so what if I use tens of thousands of transistors to represent an x86 cpu ?? the size of a warehouse buts its not emulation just because it was re-created differently.
Mona Lisa copied by a painter dot for dot is fpga
Mona Lisa emulated would be a painter in a different room having the Mona Lisa explained to the painter and the painter guessing best he/she can, the better the description the more accurate the emulated Mona lisa would be, never perfect or exactly the same.
quote from elsewhere
Now, "arbitrarily" picking Gyruss (because it's a favorite game) it has:
2x Z80
5x Ay-3-8910
1x DAC
1x 8039
1x 6809
Consider that's 10 processors, 9 if you skip the sound DAC. Plus all the housekeeping like ram/rom & memory mapping, video, controllers, and glue to bring it all together. An FPGA is going have each of these cores and other circuitry "running" simultaneously. Because it IS the actual circuit! The FPGA has become the circuit. Each gate from the target (6502 for example) has an equivalent dedicated gate wired up in the FPGA.
Whereas an emulator is going to run them sequentially. With the input of one device waiting on the output of another, right on down the line till one clock cycle is completed.