The Model M6-1 was a wide range of IBM ThinkPad portable computer keyboard assemblies produced between 1993 and 1997. Model M6-1 was a minor revision of the original Model M6 buckling sleeves keyboard assembly, with the main change being how the keyboard supports being mounted into a laptop. The Model M6-1 saw much wider adoption than its predecessor, first known to be used on the IBM ThinkPad 750 series and last known to be used on the IBM RS/6000 Notebook 860. M6-1s were largely produced by Lexmark, however, assemblies built after April 1996 were produced by Key Tronic to the same specifications and thus should not be confused with Key Tronic's own buckling sleeves keyboard implementation used on the IBM ThinkPads 701C series. As with the M6, M6-1s were essentially an evolution of the Model M3/M4 buckling sleeves keyboard that further compacted the form factor and slightly altered the buckling sleeves switch to use a barrel-based slider actuator instead of a keycap-based rod actuator for registering keypresses when the key is pressed down.