The 1984-debuting IBM Wheelwriters 3 and 5 and Quietwriter 7 were the first vessels of membrane buckling spring keyboards. What would become the Model M as we know them featured on all subsequent IBM and later Lexmark Wheelwriters for the next decade. The layouts of these keyboard assemblies were vaguely PC-like, with a max of T-nav arrow keys, one or two columns of left-side function keys, and occasionally even a numeric keypad section included on various models depending on their market segment. As a result, most Wheelwriter keyboards range from approximately 65% to 80% size layouts. The common feature amongst all of them was a split spacebar with the smaller "Code" key being an additional modifier for accessing functions throughout the keyboard.