The IBM Personal System/2 L40SX was an early laptop that featured IBM's first buckling sleeves keyboard assembly, which represented the first step of a major divergence in the Model M family that broke the largely buckling springs-based paradigm. Whilst not specifically designated a Model M, the L40SX's numeric keypad option with the same switches and the discrete Model M4 keyboards that used the same assemblies were designated members of the Model M family, and this was the origin for both. The 1992-launched IBM CL57SX also possessed the same buckling sleeves keyboard assembly, albeit in black and had an overlayed numeric keypad layer much like the SSK.