The 4600 is an i865G (built in video) chipset motherboard based computer, 5.1 sound, 10/100 NIC, front and rear usb & sound, with a lower end case. The 400SC uses the higher end i875p chipset (cheap video card in PCI slot), has greater expandibility, 2.0 sound, 10/100/1000 NIC, , rear usb & sound, and a clamshell type quietcase. Both have AGP 8x, 4 DIMM slots (dual channel capable), S-ATA, etc.