Personal digital assistants (PDAs) are handheld computers that were originally designed as personal organizers, but became much more versatile over the years. PDAs are also known as pocket computers or palmtop computers. PDAs have many uses: calculation, use as a clock and calendar, accessing the Internet, sending and receiving E-mails, video recording, typewriting and word processing, use as an address book, making and writing on spreadsheets, use as a radio or stereo, playing computer games, recording survey responses, and Global Positioning System (GPS). Newer PDAs also have both color screens and audio capabilities, enabling them to be used as mobile phones (smartphones), web browsers, or portable media players. Many PDAs can access the Internet, intranets or extranets via Wi-Fi, or Wireless Wide-Area Networks (WWANs). One of the most significant PDA characteristics is the presence of a touch screen.

History
Currently, a typical PDA has a touch screen for entering data and a memory card slot for data storage and IrDA, Bluetooth and WIFI for connectivity.

Typical features
Many original PDAs, such as the Apple Newton and the Palm Pilot, featured touch screens for user interaction, having only a few buttons usually reserved for shortcuts to often used programs. Touch screen PDAs, including Windows Pocket PC devices, usually have a detachable stylus that can be used on the touch screen. Interaction is then done by tapping the screen to activate buttons or menu choices, and dragging the stylus to, for example, highlight. Text input is usually done in one of two ways:
PDAs for business use, including the BlackBerry and Treo, have full keyboards and scroll wheels or thumb wheels to facilitate data entry and navigation, in addition to supporting touch-screen input. There are also full-size foldable keyboards available that plug directly, or use wireless technology to interface with the PDA and allow for normal typing. BlackBerry also has additional functionality as push based email and applications.
Newer PDAs, such as the Apple iPhone include new user interfaces using other means of input. The iPhone uses a technology called Multi-touch which uses fingers as input. Whereas the MacsturSoft version contains a slightly different version of Multi-Touch which is more advanced than Apple's Technology. Recognition and computation of handwritten horizontal and vertical formulas such as "1 + 2 =" was also under development. Touch screen
Although many early PDAs did not have memory card slots, now most have either an SD (Secure Digital) and/or a Compact Flash slot. Although originally designed for memory, SDIO and Compact Flash cards are available for such things as Wi-Fi and Webcams. Some PDAs also have a USB port, mainly for USB flash drives.

Memory cards
While many earlier PDAs connected via serial ports or other proprietary format, many today connect via USB cable. This served primarily to connect to a computer, and few, if any PDAs were able to connect to each other out of the box using cables, as USB requires one machine to act as a host - functionality which was not often planned. Some PDAs were able to connect to the internet, either by means of one of these cables, or by using an extension card with an ethernet port/RJ-45 adaptor.

Wired connectivity
Most modern PDAs have Bluetooth wireless connectivity, an increasingly popular tool for mobile devices. It can be used to connect keyboards, headsets, GPS and many other accesories, as well as sending files between PDAs. Many mid-range and superior PDAs have Wi-Fi/WLAN/802.11-connectivity, used for connecting to Wi-Fi hotspots or wireless networks. Older PDAs predominantly have an IrDA (infrared) port; however fewer current models have the technology, as it is slowly being phased out due support for Bluetooth and Wi-Fi. IrDA allows communication between two PDAs, a PDA and any device with an IrDA port or adapter. Most universal PDA keyboards use infrared technology because many older PDAs have it, and infrared technology is low-cost.

Wireless connectivity
An important function of PDAs is synchronizing data with a PC. This allows up-to-date contact information stored on software such as Microsoft Outlook or ACT! to update the database on the PDA. The data synchronization ensures that the PDA has an accurate list of contacts, appointments and e-mail, allowing users to access the same information on the PDA as the host computer.
The synchronizing also prevents the loss of information stored on the device in case it is lost, stolen, or destroyed. Another advantage is that data input is usually a lot quicker on a PC, since text input via a touch screen is still not quite optimal. 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 PC. This is done through synchronization software provided with the handheld, such as HotSync Manager, which comes with Palm OS handhelds, Microsoft ActiveSync for older versions of Windows or Windows Mobile Center on Windows Vista, which comes with Windows Mobile handhelds.
These programs allow the PDA to be synchronized with a Personal information manager. This personal information manager may be an outside program or a proprietary program. For example, the BlackBerry PDA comes with the 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 Palms such as the Treo 650 has the built-in ability to sync to Palm Desktop and/or Microsoft Outlook. Third-party synchronization software is also available for many PDAs from companies like Intellisync and CompanionLink. This software synchronizes these handhelds to other personal information managers which are not supported by the PDA manufacturers, such as GoldMine and Lotus Notes.

Synchronization
As with personal computers, it is possible to install additional software on most PDAs. Software can be bought or downloaded from the Internet, allowing users to personalize their PDAs to their liking. An example of this would be the display theme for the PDA. Almost all PDAs also allow for adding some form of hardware. The most common is a memory card slot, which allows the users to get additional and exchangeable storage space on their handheld devices. There are also miniature keyboards that can be connected to most mainstream PDAs for quicker text input. PDAs with Bluetooth use Bluetooth-enabled devices like headsets, mice and foldable keyboards.

Customization
PDAs are used to store information that can be accessed any time and any where.

Uses
Many PDAs are used in car kits and are fitted with differential Global Positioning System (GPS) receivers to provide realtime automobile navigation. Most systems can also display traffic conditions, dynamic routing and roadside mobile radar guns. This information is usually downloaded from the Internet prior to travel, or can be downloaded on the fly with PDAs equipped with GPRS technology. Popular software in Europe for this functionality is TomTom software showing road conditions and 3D environments. PDAs are increasingly being fitted as standard on new cars.

Automobile navigation
For many years businesses and government organizations have relied upon rugged PDAs for mobile data applications. Typical applications include supply chain management in warehouses, package delivery, route accounting, medical treatment and record keeping in hospitals, facilities maintenance and management, parking enforcement, access control and security, capital asset maintenance, meter reading by utilities, and "wireless waitress" applications in restaurants and hospitality venues. There are even PDAs designed to take significant amounts of punishment, probably meant for military use. Unfortunately, these devices often lack the features of other PDAs, and come with a steep price tag.[1]

Ruggedized PDAs
In medicine, PDAs have been shown to aid diagnosis and drug selection and some studies have concluded that their use by patients to record symptoms improves the effectiveness of communication with hospitals during follow-up. The first landmark study in testing the effectiveness of PDAs in a medical setting was conducted at the Brigham & Women's Hospital and Massachusetts General Hospitals in affiliation with Harvard Medical School. Led by the team of Steven Labkoff, MD and Sandeep Shah, the Constellation project used Apple's Newton (first PDA in the market) to cater to the demands of the medical professionals.
Constellation's objective was to test how clinicians in various medical environments (wired vs un wired) would use medical reference books on a hand-held device. The study validated the hypothesis that PDAs with medical content would be used to a greater degree (>40% more often) in unwired environments.
Today, the company evolved from the effort Skyscape offers a wide range of resources including drug information, treatment options, guidelines, evidence based information and journal summaries including the drug & safety alerts. Other entrants include Epocrates and ABX guide, which supply drug databases, treatment information and relevant news in formats specific to mobile devices and services such as AvantGo translate medical journals into readable formats and provide updates from journals. WardWatch organizes medical records to remind doctors making ward rounds of information such as the treatment regimens of patients and programs. Finally, Pendragon and Syware provide tools for conducting research with mobile devices, and connecting to a central server allowing the user to enter data into a centralized database using their PDA. Additionally, Microsoft Visual Studio and Sun Java provide programming tools for developing survey instruments on the handheld. These development tools allow for integration with SQL databases that are stored on the handheld and can be synchronized with a desktop/server based database. Recently the development of Sensor Web technology has led to discussion of using wearable bodily sensors to monitor ongoing conditions like diabetes and epilepsy and alerting medical staff or the patient themselves to the treatment required via communication between the web and PDAs.
Medical and scientific uses
As mobile technology has become almost a necessity, it is no surprise that personal computing has become a vital learning tool by this time. Educational institutes have commenced a trend of integrating PDAs into their teaching practices (mobile learning). With the capabilities of PDAs, teachers are now able to provide a collaborative learning experience for their students. They are also preparing their students for possible practical uses of mobile computing upon their graduation.
PDAs and handheld devices have recently allowed for digital note taking. This has increased student's productivity by allowing individuals to quickly spell-check, modify, and amend their class notes or e-notes. Educators are currently able to distribute course material through the use of the internet connectivity or infrared file sharing functions of the PDA. With concerns to class material, textbook publishers have begun to release e-books, electronic textbooks, which can be uploaded directly to a PDA. This eliminates the exhausting effort of carrying multiple textbooks at one time.
To meet the instructive needs sought by educational institutes, software companies have developed programs with the learning aspects in mind. Simple programs such as dictionaries, thesauri, and word processing software are important to the digital note taking process. In addition to these simple programs, encyclopedias and digital planning lessons have created added functionality for users.
With the increase in mobility of PDAs, school boards and educational institutes have now encountered issues with these devices. School boards are now concerned with students utilizing the internet connectivity to share test answers or to gossip during class time, which creates disruptions. Many school boards have modernized their computer policies to address these new concerns. Software companies such as Scantron Corp. have now created a program for distributing digital quizzes. The quiz software disables the infrared function on PDAs, which eliminates the element of information sharing among individuals during the examination.[2]

Educational uses
PDAs are used by glider pilots for pre-flight planning and to assist navigation in cross-country competitions. They are linked to a GPS to produce moving-map displays showing the tracks to turn-points, airspace hazards and other tactical information.

Sporting uses

Technical details
Many PDAs run using a variation of the ARM architecture (usually denoted by the Intel XScale trademark). This encompasses a class of RISC microprocessors that are widely used in mobile devices and embedded systems, and its design was influenced strongly by a popular 1970s/1980s CPU, the MOS Technology 6502.

Architecture
The currently major PDA operating systems are:

Palm OS - owned by PalmSource
Windows Mobile (Pocket PC), (based on the Windows CE kernel) - owned by Microsoft
BlackBerry OS - owned by Research In Motion
Many operating systems based on the Linux kernel - free (not owned by any company) These include

• Familiar (comes in three flavours: GPE, Opie and barebone)
  OpenZaurus (for Zaurus PDAs)
  Intimate (for PDAs with an exceedingly large amount of memory)
  Symbian OS (formerly EPOC) owned by Motorola, Panasonic, Nokia, Samsung, Siemens and Sony Ericsson
  Windows Vista - owned by Microsoft; has seldom use on PDAs; but may become more common on them if the OQO Model 2 sells well. Increasing popularity
  Perhaps, more than any other computer devices, the PDA lacks the fully-blown infrastructure of a Wireless Broadband network. This could be offered in future by WiMax. Nowadays prices of laptops are coming down. Though somewhat bigger in size, laptops have better visibility and are more powerful. However, the OQO Model 2 has been released as an IBM-PC compatible PDA with a USB port so that people can play computer games from ubiquitous operating systems such as Windows XP and connect typical PC peripherals.
  
  Shortcomings
  
  HP iPAQ
  Psion
  Abacus PDA Watch
  Acer N Series
  AlphaSmart
  Amida
  BlackBerry
  Casio Pocket Viewer
  Dell Axim
  Fujitsu Siemens Loox
  GMate Yopy
  High Tech Computer Corporation's series of Windows Mobile PDA/phones
  Palm, Inc. (Tungsten E2, TX, Treo and Zire)
  OQO Model 2; the only IBM PC compatible in the form factor of a PDA.
  PocketMail (email PDA with inbuilt acoustic coupler)
  Sharp Wizard and Sharp Zaurus Popular consumer PDAs
  
  hp Jornada Pocket PC (phased out/merged with iPAQ line in 2002)
  Sony CLIÉ (discontinued)
  Tapwave Zodiac (discontinued)
  LifeDrive(discontinued)
  Apple Newton (discontinued)
  Dell Axim (discontinued) Rugged PDAs for business, government and military applications
  
  Automotive navigation system
  Danger Hiptop
  Desknote
  Graffiti (Palm OS)
  Hipster PDA
  Information appliance
  Laptop
  Mobile software
  Mobile learning
  Mobile web
  PADD (Star Trek PDA)
  Personal area network
  Personal Communicator
  Personal information manager
  Smartphone
  Sony Clie
  Subnotebook
  Tablet PC
  Ultra-Mobile PC
  Wearable computer
  Sena Cases
  Timex Datalink