The MCP655, as it comes from Laing, is the bare bones D5 pump Swiftech also sells as an OEM device. If you fancied a top from someone else, this is the SKU to go for. Most first-timers would want to get a pump and top combo unit, however, and that is where the acrylic or acetal top versions come in. The MCP655 with a PWM motor is rapidly gaining popularity due to motherboard makers recognizing and supporting PWM fans and pumps alike, and Swiftech sent us the MCP655-PWM-Acrylic SKU accordingly.