A traditional keyboard is rectangular and has a constant slope, from highest at the rear to lowest at the front. These keyboards are available in various footprints, including standard (19" x 8"); midsize (18" x 7"); and space-saver (17" x 6.5" or less). Size is important to the extent that large keyboards occupy considerable desk space and may not fit some keyboard drawers.
An ergonomic keyboard uses a split face and variable slopes, which allow more natural and comfortable hand and wrist positions. Most ergonomic keyboards are as large as or larger than standard traditional keyboards, not least because they include a built-in wrist rest. Some claim that ergonomic keyboards help reduce Repetitive Stress Injury (RSI) problems such as Carpal Tunnel Syndrome (CTS), but we have seen no credible evidence to support these claims. The secret to avoiding such problems, regardless of what keyboard style you use, is to take frequent breaks and to avoid using the keyboard continuously for more than an hour or so at a time.