The Space Saving Keyboard (SSK) were the tenkeyless and compacted version of the IBM Enhanced Keyboards originally available as an option for the IBM Personal System/2 series of computers. These are perhaps the most well-known Model M variant besides the Enhanced Keyboard. The fact that they weren't bundled with any systems and numeric keypads were viewed more favourably during the '80s, SSKs are relatively rare. As an attempt to provide an alternative to the loss of the numeric keypad, a togglable numeric keypad layer is present across the right side of the alphanumeric keys. They have since been spiritually succeeded by the Unicomp Mini Model M, which compared to the SSK feature a Type-A USB based module cable, lock-lights, black casing, Windows/GUI keys, and an upgraded membrane design.