Ever have a problem on your Mac, where you can’t type the letters and numbers 7, 8, 9, U, I, O, J, K, L, and M—and maybe some others?
It’s probably Mouse Keys at play, an accessibility feature in macOS that mimics an old IBM-style keypad feature.
Num Lock and its computer history
Keyboards still have vestiges of their origins on typewriters and mechanical calculators. We mostly ignore those in our day-to-day work. The Shift key, originally meant to literally raise a set of typebars in a typewriter, merely shifts among upper and lower case. And you know better than to press Caps Lock when entering passwords—Apple even alerts you when you have it accidentally enabled.