3Additional InformationThis section provides information for the additional features that are part of your computer.Memory Module GuidelinesTo ensure optimal performance of your computer, observe the following general guidelines when configuring yoursystem memory:• Memory modules of different sizes can be mixed (for example, 2 GB and 4 GB), but all populated channels musthave identical configurations.• Memory modules must be installed beginning with the first socket.NOTE: The memory sockets in your computer may be labelled differently depending on the hardware configuration.For example, A1, A2 or 1,2,3.• If the quad-rank memory modules are mixed with single or dual-rank modules, the quad-rank modules must beinstalled in the sockets with the white release levers.• If memory modules with different speeds are installed, they operate at the speed of the slowest installedmemory module(s).Power Supply Unit (PSU) LockThe PSU lock prevents the removal of the PSU from the chassis.NOTE: To lock or unlock the PSU, always ensure that the cover of the chassis is removed. For information onremoving the cover, see Removing the cover.To secure the PSU, remove the screw from the unlock screw location and tighten the screw to the lock location.Similarly, to unlock the PSU, remove the screw from the lock screw location and tighten the screw to the unlock screwlocation.37