Your Mac won’t type U, I, O, J, K, L, and M? Here’s why

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.

mac911 ibm numpad IDG

Early 84-key IBM keyboards had a numeric keypad that
doubled as arrow and other keys for text-screen-based
interactions.

The Num Lock key was a product of the intermediate age, where
mechanical and digital met. Some IBM computer keyboards didn’t
have separate arrow keys, but they did have a numeric keypad
for fast number entry. IBM doubled up: It added a Num Lock key
that flipped the numeric keypad to act as arrow keys to move a
cursor around a screen-based interface, before computer mouses.

On certain laptops, including older Macs, Num Lock had a
different function. Lacking a numeric keypad, Num Lock turned
part of the main keyboard into a pseudo-keypad. (There was
sometimes a unique Num Lock key, sometimes it doubled with a
Clear key and Shift, and sometimes it was a function to invoke,
like through F6 on a Mac.)

The pseudo-keypad layout relied on sets of four keys starting
with 7, 8, 9, 0 and going down three rows to M. With this mode
invoked, you could still type 7, 8, 9, and 0 and have those
characters appear, as they’re still mapped to the same
position. But U, I, O, P, J, K, l, semicolon, M, command,
period, slash take on keypad functions.

mac911 tibook keyboard numpad
IDG

The PowerBook and some early MacBooks had numeric keypad
symbols overlaying part of the main keyboard.

Apple stopped supporting Num Lock via F6 quietly back in 2008. It shouldn’t be
possible to invoke this mode accidentally, as it shouldn’t
exist. It’s available in Boot Camp with some laptops, although
Apple doesn’t specify which.

An independent developer did create
a Num Lock app
—called simply NumLock—that would invoke the
feature within Mac OS X; it hasn’t been updated in a few years,
and I haven’t tested it in Mojave.

Mouse Keys and its modern usage

Apple lets you hearken back to those IBM days with an
accessibility feature in macOS called Mouse Keys. With Mouse Keys enabled in
the Accessibility preference pane in the Mouse & Trackpad
section, the number keys on a keypad turn into cursor diagonal,
left, right, up, and down cursor movement in tiny increments—or
hold down and it moves faster. To click the mouse, press 5; to
click and hold, press 0; to release, press the dot on the
keypad.

mac911 mouse keys apple
Apple

Mouse Keys remaps keys to cursor movement and mouse actions
as an accessibility feature.

However, if you’re using a laptop or a keyboard without a
keypad, Mouse Keys hijacks a subset of that old IBM layout. 7,
8, 9, I, O, P, J, K, L, M, and period are turned into the same
layout as a keypad (789/456/123/0.).

One Macworld reader has found that a keyboard they plugged in
invoked Mouse Keys even though they didn’t know it was turned
on. You can disable Mouse Keys via the Accessibility preference
pane, but if you haven’t changed defaults, you can also tap the
Option key five times and an onscreen accessibility message
appears briefly noting it’s turned off. You can similarly
re-enable it the same way.

This Mac 911 article is in response to a question submitted
by Macworld reader Trang.

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