Most standard keyboards consist of 101 keys. They rely on an alphanumeric layout handed down from old typewriters. The extra keys give you options for controlling software and computer functions -- a duty, old typewriters never needed to address.

Aside from alphanumeric characters, a keyboard's main components include:

Function keys. These consist of 10 to 15 keys labeled with the letter F and a number; for instance, "F1," "F2," "F3," etc. Older keyboards featured the function keys on the left-hand side, while newer ones tend to place them across the top. Function keys let you operate software applications -- such as a word processor or a spreadsheet -- more efficiently. A program may tell you to press a certain function key to bring up a particular menu or carry out a specific function, like changing a font or displaying a row of invoice data. More complex applications may include a card that users can place over the function row, effectively labeling the keys for functions specific to that program.

Control keys. The "control," "alt" ("option" on Macintoshes) and "command" ("apple") keys add functionality to the other keys. Pressed simultaneously with the other keys, much like shift buttons, they allow the user to execute more complex commands, such as saving; moving a word, sentence or paragraph inside a document; or any number of functions that would otherwise require users to take their hands off the keyboard and use the mouse and drop-down menus.

Numeric keypad. A numeric keypad consists of a block of number keys similar to that of a calculator; it lets you type numbers rapidly. Numeric keypads co-exist peacefully with the row of numbers found above the alphabetical keys, which is generally used for adding occasional numbers into text documents.

Directional keys. Keyboards usually feature a block of four keys with directional arrows that help you navigate quickly through text and other documents. The inverted-T configuration is the most common and is far more intuitive than the layout featured on many laptop computers, in which the four keys are in a row. Typical keyboards also present six buttons above the directional keys, usually labeled "page up," "page down," "home," "end," "delete" and "insert," for one-hit execution of those commands.

Despite their similarities, not all keyboards are alike. Characteristics that distinguish one model of keyboard from the next include:

Design. Only for the past few years have manufacturers been pairing full-size keyboards with new computers. Some computers still ship with simpler keyboards that lack numeric keypads, function keys and directional keys. The extra buttons are worth investigating: While mice and other pointing devices have increased flexibility, people who do data entry or work with text documents often find that it's faster to move around the screen with directional keys than to take their hands off the keyboard to use a mouse.

Ergonomic keyboards are widely used, which are designed to better fit the hands, wrists and body, and, it is hoped, to provide a more natural (and comfortable) way of typing. The traditional rectangular keyboards are being enhanced with wrist rests and mechanisms that allow you to angle the keyboard to your liking. Other keyboards depart from the traditional rectangular design radically, splitting the board into two pieces that can be adjusted to keep the wrists even while typing.

Sound. Some keyboards are silent when keys are pressed, while others produce a clicking sound.

Feel. Keyboard keys range from feeling mushy when pressed to an extra-crisp feel with a lot of resistance. This all depends on how the keyboard was built. Some manufacturers allow you to change the resistance of the keys, if you don't mind removing all the buttons and replacing the springs (be they metal, rubber or plastic).