Apple's website mentions only RAM and flash storage as user-serviceable, though third party tear-downs show nearly all components can be removed and replaced. However, special tools only available from Apple are necessary for proper dismantling and reassembly. Apple has also specified mandatory and recommended tightening torque values for nearly every screw, with the most important being those securing the GPUs and CPU riser card to the thermal core. According to Apple, not tightening screws to the mandatory torque values may result in damage or malfunction. A lock switch on the aluminum housing allows for easy access to the internals, as well as fitting a security lock with its own cable, and components are secured with Torx screws. The flash storage and GPUs use proprietary connectors and are specially sized to fit into the enclosure. The CPU is not soldered to the riser card and can be replaced with another LGA 2011 socket processor, including processor options not offered by Apple. The type of RAM modules that Apple supplies with the late-2013 Mac Pro in the default configuration are ECC (UDIMM) on the up to 8 GB modules (shown on each module as "PC3-14900E"). Apple offers as an optional upgrade 16 GB modules are ECC (RDIMM) modules (shown on each module as "PC3-14900R"). The higher-capacity 32 GB modules that some third-party vendors offer are also RDIMM. The UDIMM and RDIMM module types cannot be mixed. Apple publishes recommended configurations to use.