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Typematic Features (Repeat Delay and Repeat Rate)

A useful feature found on all systems today is the ability to have a stream of character codes generated automatically when you hold down a key for a period of time. This is called typematic and has been around for quite a long time. It is only of use in certain circumstances of course, but where it is of use, it is indispensable. For example, consider using the arrow keys to move around in a text file, or the <Page Down> key to scroll through a long document. Typematic prevents you having to hit the appropriate key literally hundreds of times in a row.

Typematic can be implemented at almost any level of hardware or software that falls somewhere between the physical keycaps and your application software. More specifically, typematic functions have been implemented in the following ways in the PC:

• Within the keyboard itself, by the internal keyboard controller
• By the system BIOS
• By the operating system

It's even possible to have a particular application do its own Typematic functions but that's generally not done, except perhaps in some games. Is doing Typematic in hardware better than software, or vice-versa? It depends on your needs and wants. Typematic at the keyboard level can be useful, as it will function the same for all software you use. However, some find it more convenient to use the BIOS or operating system for these functions. For USB you may find your options more limited (BIOS controls may not work for these keyboards.)

There are two key parameters that control the typematic feature:

• Repeat Delay: This is the length of time that a key must be held down before the typematic feature is activated. Each time you release a key and press a new one, the delay "countdown" is reset. The larger the value, the longer each key must be held down before key repetition begins. If it is set too small, you may get keys repeating when you don't want them to.
• Repeat Rate: This sets the frequency with which characters will be sent once the typematic feature is activated.

If you have a keyboard that has built in typematic features, you'll generally set up the feature using special key sequences; refer to your manual or the manufacturer's web site for the commands you need. For BIOS-activated typematic, set the appropriate parameters as described in this section. For Windows, use the keyboard applet in the Control Panel, which has sliders for delay and repeat rate. For DOS, you need to use the MODE command with its strange assignment numbers, as described here.

Next: Accessibility Features (StickyKeys, FilterKeys and ToggleKeys)

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