The Palm Zire 21 Handheld PDA is a digital organizer featuring a touchscreen interface and Palm OS operating system. With 8 MB of installed memory and a 160 x 160 black and white LCD display, this handheld device offers a compact and efficient way to manage tasks, calendar, and notes on the go. Palm's reputation for reliability and user-friendly design make the Zire 21 a popular choice for those looking for a convenient and reliable digital planner.