Personal Digital Assistants

Personal digital assistants (PDAs) are handheld computers, initially marketed as electronic replacements for paper pocket organizers like the Filofax. In many cases, PDAs have evolved to include important utilities with functions far beyond simply scheduling appointments, storing phone numbers, and making shopping lists; today, many PDAs are wireless Internet devices capable of receiving email and downloading information off the Internet. Some even double as cellular phones or digital music players. They are expected to be important tools for mobile communications and e-commerce within the next few years, as people buy products aimed at keeping them connected to their information wherever they go.

In essence, PDAs are smaller, handheld versions of personal computers, reduced in size to make them even more portable than laptop PCs. Like any standard desktop PC or laptop, PDAs are powered by microprocessors that coordinate their utilities. Like computers, they have operating system (OS) software; in fact, Microsoft adapted its Windows OS for use in handhelds, calling the PDA version Windows CE. The most popular PDAs are small enough to fit comfortably in a shirt pocket, functioning as a kind of carry-along personal database.

There are two types of PDAs. “Hand-held computers,” the larger of the two, have a larger liquid crystal display (LCD) interface, and often employ a small keyboard with optional touch-screen software for data entry. These often are Windows CE, or as they were later known, Pocket PC-styled devices, and contain complex computer programs, making them literally palm-sized personal computers. On the other hand, “palm-sized computers,” the Palm Pilot-styled devices, are smaller and lighter, with less screen-display space, and usually with less complex computing power. These usually rely on a pen-shaped stylus used to tap virtual keys or to scrawl along the surface of the LCD screen, to write data into the device.

In both PDA types, handwriting recognition programs can be used to input data. Both also are battery-powered, whether by AAA alkaline batteries or by rechargeable lithium, nickel-cadmium, or nickel-metal hydride cells. Battery life usually depends on how many and what kinds of programs the device runs. Some PDA batteries can last several weeks with regular usage, others just a couple of hours if the PDA is running complex software like music players.

Since PDAs have no hard drives, they store their core programs on solid-state, read-only memory (ROM) chips, which hold data even if a device is not powered up—but not if the batteries die. Any data or additional programs uploaded after purchase are stored in the device's random-access memory (RAM). PDAs usually contain no less than 2MB (megabytes) of memory, enough to store 4,000 address entries and 100 email messages, but some have much more. Microsoft's revamped Pocket PC has a complex Windows-styled OS that operates such programs as Word and Excel, so it contains up to 32MB of memory. The Palm operating system is far simpler, taking up less than 100KB (kilobits) of total memory—about 1 percent the space eaten up by Windows 98. Therefore, the Palm OS needs less preinstalled memory. The memory on many PDAs can be upgraded, however.

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