A typical PDA has a touchscreen for navigation, a memory card slot for data storage, and IrDA, Bluetooth and/or Wi-Fi. However, some PDAs may not have a touchscreen, using softkeys, a directional pad, and a numeric keypad or a thumb keyboard for input. To have the functions expected of a PDA, a device's software typically includes an appointment calendar, a to-do list, an address book for contacts, a calculator, and some sort of memo (or "note") program. PDAs with wireless data connections also typically include an email client and a Web browser, and may or may not include telephony functionality.
PalmPilot organiser on display at the Musée Bolo, EPFL, Lausanne
Many of the original PDAs, such as the Apple Newton and Palm Pilot, featured a touchscreen for user interaction, having only a few buttons—usually reserved for shortcuts to often-used programs. Some touchscreen PDAs, including Windows Mobile devices, had a detachable stylus to facilitate making selections. The user interacts with the device by tapping the screen to select buttons or issue commands, or by dragging a finger (or the stylus) on the screen to make selections or scroll.
Typical methods of entering text on touchscreen PDAs include:
- A virtual keyboard, where a keyboard is shown on the touchscreen. Text is entered by tapping the on-screen keyboard with a finger or stylus.
- An external keyboard connected via USB, Infrared port, or Bluetooth. Some users may choose a chorded keyboard for one-handed use.
- Handwriting recognition, where letters or words are written on the touchscreen, often with a stylus, and the PDA converts the input to text. Recognition and computation of handwritten horizontal and vertical formulas, such as "1 + 2 =", may also be a feature.
- Stroke recognition allows the user to make a predefined set of strokes on the touchscreen, sometimes in a special input area, representing the various characters to be input. The strokes are often simplified character shapes, making them easier for the device to recognize. One widely known stroke recognition system is Palm's Graffiti.
Despite research and development projects, end-users experience mixed results with handwriting recognition systems. Some find it frustrating and inaccurate, while others are satisfied with the quality of the recognition.
Touchscreen PDAs intended for business use, such as the BlackBerry and Palm Treo, usually also offer full keyboards and scroll wheels or thumbwheels to facilitate data entry and navigation. Many touchscreen PDAs support some form of external keyboard as well. Specialized folding keyboards, which offer a full-sized keyboard but collapse into a compact size for transport, are available for many models. External keyboards may attach to the PDA directly, using a cable, or may use wireless technology such as infrared or Bluetooth to connect to the PDA. Newer PDAs, such as the HTC HD2, Apple iPhone, Apple iPod Touch, and Palm Pre, Palm Pre Plus, Palm Pixi, Palm Pixi Plus, Google Android (operating system) include more advanced forms of touchscreen that can register multiple touches simultaneously. These "multi-touch" displays allow for more sophisticated interfaces using various gestures entered with one or more fingers.
Although many early PDAs did not have memory card slots, now most have either some form of Secure Digital (SD) slot, a CompactFlash slot or a combination of the two. Although designed for memory, Secure Digital Input/Output (SDIO) and CompactFlash cards are available that provide accessories like Wi-Fi or digital cameras, if the device can support them. Some PDAs also have a USB port, mainly for USB flash drives. Some PDAs use microSD cards, which are electronically compatible with SD cards, but have a much smaller physical size.
While early PDAs connected to a user's personal computer via serial ports or another proprietary connection, many today connect via a USB cable. Older PDAs were unable to connect to each other via USB, as their implementations of USB didn't support acting as the "host". Some early PDAs were able to connect to the Internet indirectly by means of an external modem connected via the PDA's serial port or "sync" connector, or directly by using an expansion card that provided an Ethernet port.
Most modern PDAs have Bluetooth, a popular wireless protocol for mobile devices. Bluetooth can be used to connect keyboards, headsets, GPS receivers, and other nearby accessories. It's also possible to transfer files between PDAs that have Bluetooth. Many modern PDAs have Wi-Fi wireless network connectivity and can connect to Wi-Fi hotspots. All smartphones, and some other modern PDAs, can connect to Wireless Wide Area Networks, such as those provided by cellular telecommunications companies. Older PDAs from the 1990s to 2006 typically had an IrDA (infrared) port allowing short-range, line-of-sight wireless communication. Few current models use this technology, as it has been supplanted by Bluetooth and Wi-Fi. IrDA allows communication between two PDAs, or between a PDA and any device with an IrDA port or adapter. Some printers have IrDA receivers, allowing IrDA-equipped PDAs to print to them, if the PDA's operating system supports it. Universal PDA keyboards designed for these older PDAs use infrared technology. Infrared technology is low-cost and has the advantage of being allowed aboard.
Most PDAs can synchronize their data with applications on a user's computer. This allows the user to update contact, schedule, or other information on their computer, using software such as Microsoft Outlook or ACT!, and have that same data transferred to PDA—or transfer updated information from the PDA back to the computer. This eliminates the need for the user to update their data in two places. Synchronization also prevents the loss of information stored on the device if it is lost, stolen, or destroyed. When the PDA is repaired or replaced, it can be "re-synced" with the computer, restoring the user's data. Some users find that data input is quicker on their computer than on their PDA, since text input via a touchscreen or small-scale keyboard is slower than a full-size keyboard. Transferring data to a PDA via the computer is therefore a lot quicker than having to manually input all data on the handheld device.
Most PDAs come with the ability to synchronize to a computer. This is done through synchronization software provided with the handheld, or sometime with the computer's operating system. Examples of synchronization software include:
- HotSync Manager, for Palm OS PDAs
- Microsoft ActiveSync, used by Windows XP and older Windows operating systems to synchronize with Windows Mobile, Pocket PC, and Windows CE PDAs, as well as PDAs running iOS, Palm OS, and Symbian
- Microsoft Windows Mobile Device Center for Windows Vista, which supports Microsoft Windows Mobile and Pocket PC devices
- Apple iTunes, used on Mac OS X and Microsoft Windows to sync iOS devices (such as the iPhone and iPod touch)
- iSync, included with Mac OS X, can synchronize many SyncML-enabled PDAs
- BlackBerry Desktop Software, used to sync BlackBerry devices.
These programs allow the PDA to be synchronized with a personal information manager, which may be part of the computer's operating system, provided with the PDA, or sold separately by a third party. For example, the RIM BlackBerry comes with RIM's Desktop Manager program, which can synchronize to both Microsoft Outlook and ACT!. Other PDAs come only with their own proprietary software. For example, some early Palm OS PDAs came only with Palm Desktop, while later Palm PDAs—such as the Treo 650—have the ability to sync to Palm Desktop or Microsoft Outlook. Microsoft's ActiveSync and Windows Mobile Device Center only synchronize with Microsoft Outlook or a Microsoft Exchange server. Third-party synchronization software is also available for some PDAs from companies like CommonTime and CompanionLink. Third-party software can be used to synchronize PDAs to other personal information managers that are not supported by the PDA manufacturers (for example, GoldMine and IBM Lotus Notes).
Some PDAs can synchronize some or all of their data using their wireless networking capabilities, rather than having to be directly connected to a personal computer via a cable. Devices running Palm's webOS or Google's Android operating system primarily sync with the cloud. For example, if Gmail is used, information in contacts, email, and calendar can be synchronized between the PDA and Google's servers. RIM sells BlackBerry Enterprise Server to corporations so that corporate BlackBerry users can wirelessly synchronize their PDAs with the company's Microsoft Exchange Server, IBM Lotus Domino, or Novell GroupWise servers. Email, calendar entries, contacts, tasks, and memos kept on the company's server are automatically synchronized with the BlackBerry.