Slot type create by ASUS for HSP (Host Signal Processing) daughter boards installation, like networking and modem cards. HSP technology transfers the peripheral control to the system processor, instead of having self control. The biggest advantage of peripherals based on this technology is their price, cheaper because the electronics involved is simpler, since the peripheral doesn't have control circuitry. The biggest disavantage is that the system performance decreases, since the system CPU will have to control the peripheral thus having less resources available. This drop in performance can or cannot be perceptible, depening on your PC specs.
Physically speaking, ACR slot is equal to a PCI slot, but rotated 180 degrees. We can say that ACR is like an AMR or CNR propretary slot from ASUS.
