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[ The PC Guide | Systems and Components Reference Guide | Keyboards | Keyboard Key Groupings ]

Modification Keys

The keyboard contains several keys that serve primarily to alter the function or meaning of other keys. They are often used in combination with another key (typically by holding them down and then pressing the other key) or are used to set a particular keyboard state. I call these modification keys.

I include in this group two different sub-categories. The first are what I call temporary modification keys, because they modify other keys only while held down. This includes these:

  • <Shift> Keys: These two keys are near the bottom of the keyboard, one on either side of the main typing area. They enable access to capital letters, and also to the "alternate" functions printed on the keycaps above the unshifted symbol or function shown. So for example, holding the <Shift> key down and pressing the equal sign ("=") generates a plus sign ("+"). The <Shift> keys also change the behavior of the function keys in most software programs; for example, <Shift>+<F6> is different than just <F6>.
  • <Ctrl> Keys: These are the "control keys"; one is located on either side of the typing area. Sometimes the keycap says "Control" instead of the shortened "Ctrl". These keys are used in combination with regular alphanumeric keys and also the function keys to control special features and functions in software programs.
  • <Alt> Keys: These are the "alternate control keys". They operate the same way the <Ctrl> keys do; their presence just lets complex software have more options. For example, <Alt>+<F6> can be a different function than <Ctrl>+<F6>. The <Alt> keys are also used for ASCII code generation.

The temporary modification keys can be combined if held down. For example, you can tell Windows to launch a program if you hold down <Shift>+<Ctrl>+<Alt>+Q. Obviously, this sort of thing can make you feel like your fingers are playing "Twister" after a while. :^)

The second sub-category contains what I think of as permanent or locking modification keys. These are toggle keys, like the control of a flashlight; they change the function of other keys until they are pressed again to cancel the effect:

  • Caps Lock: When pressed, causes the function of the <Shift> keys to be reversed, but only for letter characters; other keys are unaffected. When active, the Caps Lock LED will be lit.
  • Num Lock: Enables the numbers on the numeric keypad when activated, and lights the Num Lock LED as well. When not active, the numeric keypad's keys generate cursor-control functions instead. This functionality dates back to the earliest PCs, which did not have dedicated cursor-control keys; today the cursor-control functions on the numeric keypad are redundant, which is why many people leave Num Lock always enabled.

Note: The Num Lock key is usually part of the numeric keypad physically, but I don't consider it part of the keypad logically. One of those differences I mentioned before.

  • Scroll Lock: Lights the Scroll Lock LED and causes some software programs to alter their behavior when certain other keys are pressed. In particular, when Scroll Lock is active, the cursor keys are often used to scroll the visible document rather than change position within it. This is not used nearly as much as the other two.

This table contains a full listing of the keys in this section, along with their key numbers and scan codes:

Key #


Make Code

Break Code


<Caps Lock>




<Left Shift>




<Right Shift>




<Left Ctrl>




<Left Alt>




<Right Alt>

E0 38

E0 B8


<Right Ctrl>

E0 1D

E0 9D


<Num Lock>




<Scroll Lock>



Next: Dedicated Cursor Control and Navigation Keys

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