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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 aor 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).

Wireless synchronization

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.

Apple iOS devices, like the iPhone, iPod Touch, and iPad, can use Apple's MobileMe subscription service to synchronize calendar, address book, mail account, Internet bookmark, and other data with one or more Macintosh or Windows computers using Wi-Fi or cellular data connections.

Palm's webOS smartphones primarily sync with the cloud. For example, if Gmail is used, information in contacts, email, and calendar can be synchronized between the phone 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.

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Synchronization

Most PDAs can synchronize their data with applications on a user's personal 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

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Memory cards

Although many early PDAs did not have memory card slots, now most have either some form of Secure Digital (SD) slot or a CompactFlash slot. Although originally 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.

Wired connectivity

While early PDAs connected to a user's personal computer via serial ports or another proprietary connection, many today connect via a USB cable. PDAs are not typically able to connect to each other via USB, as USB requires one machine to act as a "host," which isn't a typical PDA function.

Some early PDAs were able to connect to the Internet indirectly by means off 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.

Wireless connectivity 

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 like the Apple iPod touch, can connect to Wireless Wide Area Networks, such as those provided by cellular telecommunications companies.

Older PDAs 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. Most universal PDA keyboards use infrared technology because many older PDAs have it. Infrared technology is low-cost and has the advantage of being allowed aboard aircraft.

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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, or Bluetooth. Some users may choose a chorded keyboard for one-handed use.

* Handwriting recognition, where letters or words are written on the touchscreen, 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 rigorous 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 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 Apple iPhone, Apple iPod Touch, HTC HD2, and Palm Pre, Palm Pre Plus, Palm Pixi, Palm Pixi Plus, 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.

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A personal digital assistant (PDA), also known as a palmtop computer,is a mobile device that functions as a personal information manager. Current PDAs often have the ability to connect to the Internet. A PDA has an electronic visual display, enabling it to include a web browser, but some newer models also have audio capabilities, enabling them to be used as mobile phones or portable media players. Many PDAs can access the Internet, intranets or extranets  via Wi-Fi  or Wireless Wide Area Networks. Many PDAs employ touchscreen technology.

The term PDA was first used on January 7, 1992 by Apple Computer CEO John Sculley at the Consumer Electronics Show in Las Vegas, Nevada, referring to the Apple Newton. In 1996, Nokia introduced the first mobile phone with full PDA functionality, the 9000 Communicator, which grew to become the world's best-selling PDA. The Communicator spawned a new category of mobile phones: the smartphone. Today, the vast majority of all PDAs are smartphones. Over 150 million smartphones are sold each year, while "stand-alone" PDAs without phone functionality sell only about 3 million units per year.Popular smartphone brands include HTC, Apple, Palm, Nokia Nseries, and RIM.

Typical features

A typical PDA has a touchscreen for entering data, a memory card slot for data storage, and IrDA, Bluetooth and/or Wi-Fi. However, some PDAs may not have a touch screen, using softkeys, a directional pad, and a numeric keypad or a thumb keyboard for input; this is typically seen on telephones that are incidentally PDAs.

In order 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, and some sort of memo (or "note") program. PDAs with wireless data connections also typically include an email client and a Web browser.

Touch screen

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. Touchscreen PDAs, including Windows Mobile devices, may have 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.

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  * Business-oriented tablet personal computers have been slow sellers from 2001 to date.

  * Screen risk - Tablet computers are handled more than conventional laptops, yet many are built on similar frames; in addition, since their screens also serve as input devices, they run a higher risk of screen damage from impacts and misuse.

  * Hinge risk - A convertible tablet computer's screen hinge is often required to rotate around two axes, unlike a normal laptop screen, subsequently increasing the number of possible mechanical and electrical (digitizer and video cables, embedded WiFi antennas, etc.) failure points.

Developing programs for tablet computers

A significant trait to define whether a tablet computer can be regarded as a personal computer is the ability for the final user to install arbitrary or self-developed software. The new class of devices heralded by the iPad has spurred the tendency of a walled garden approach where the vendor reserves rights as to what can be installed. The software development kits for these platforms are restricted and the vendor must approve the final application for distribution to users. Proponents of open source software deem that these restrictions on software installation and lack of administrator rights make this category one that, in their view, cannot be properly named personal computers.But newer mobile operating system based tablet computers may abandon the walled garden concept, and be like personal computers in this regard.

Tablets in developing countries

The low hardware requirements and easy operation of tablet computers has made it subject to various design studies for use in developing countries. Prototype tablet computers such as the Sakshat have been projected to cost $35, according to researchers in India which shall be soon available for the masses as the cheapest tablet working on Android with full functionality;however the bill of materials currently comes to $47.One laptop per child (OLPC) plans to introduce a tablet computer for $100.Nicholas Negroponte, Chairman of OLPC, has invited the Indian researchers to MIT to begin sharing the OLPC design resources for their tablet computers.OLPC has been awarded a grant for an interim step to their next generation tablet, OLPC XO-3.

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Comparison with laptop computers

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The advantages and disadvantages of tablet computers are highly subjective measures. What appeals to one user may be exactly what disappoints another. The following are commonly cited opinions of tablet computers versus laptops:

Advantages

    * Usage in environments not conducive to a keyboard and mouse such as lying in bed, standing, or handling with a single hand.

    * Lighter weight, lower power models can function similarly to dedicated reading devices like the Amazon Kindle.

    * Touch environment makes navigation easier than conventional use of keyboard and mouse or touch pad in certain contexts such as image manipulation, or mouse oriented games.

    * Digital painting and image editing are more precise and intuitive than painting or sketching with a mouse.

    * The ability for easier or faster entery of diagrams, mathematical notations, and symbols.

    * Allows, with the proper software, universal input, independent from different keyboard localizations.

    * Some users find it more direct and pleasant to use a stylus, pen or finger to point and tap on objects, rather than use a mouse or touchpad, which are not directly connected to the pointer on screen.

Disadvantages

    * Higher price — convertible tablet computers can cost significantly more than non-tablet portable PCs although this premium has been predicted to fall.

    * Input speed — handwriting or typing on a virtual keyboard can be significantly slower than typing speed on a conventional keyboard, the latter of which can be as high as 50-150 WPM; however, Slideit, Swype and other technologies are offered in an effort to narrow the gap.

    * Ergonomics - a tablet computer, or a folded slate PC, does not provide room for a wrist rest. In addition, the user will need to move their arm constantly while writing.

    * Weaker video capabilities - Most tablet computers are equipped with embedded graphics processors instead of discrete graphics cards. In July 2010, the only tablet PC with a discrete graphics card was the HP TouchSmart tm2t, which has the ATI Mobility Radeon HD5450 as an optional extra.