四处 (or 四方) = north, south, east and west
八方 = (north, south, east and west) + southeast, northeast, southwest and northwest
四方 and 四处 can be used interchangeably. There is also a third one: 四面.
Another word you might want to know:
- 十面 = ((north, south, east and west) + southeast, northeast, southwest and northwest) + up and down.
八处 doesn't seem to be a thing, but 八面 does exist.