This architecture describes various devices and the applications that can be developed on them.

4.Major Players
There are several major players in this market, among them 3Com / Palm, Newton, Inc. (formerly Apple), Microsoft, Psion, Handspring, daVini, Helio, Hewlett Packard, Compaq, Franklin Rex, Sharp, and other small entrants into this market.

It is interesting to note the differences in strategy employed by various PDA manufacturers. On one end of the spectrum, Palm has decided to acknowledge the current limits of wireless computing (bandwidth, speed, power, etc.) and develop a PDA, which effectively works within those constraints at a reasonable price. Psion on the other hand has decided to continue to push current technology and offer consumers added functionality for a higher price.

There are several operating systems, which are in use in the PDA market. Some of these operating systems are in use across a number of product offerings while others are proprietary to the company that developed them. Each player is desperately trying to establish itself as the standard for PDAs. Windows CE and Palm OS are two of the major players in the operating system market. They are currently the leaders in market share.

5.Overview of Related Operating systems

5.1.PalmOS
The GUI applications that run on Palm Powered handhelds are generally single-threaded, event-driven programs. Applications run one at a time. Users do not quit or exit an application; they simply choose to run a different application. In response, the Palm OS stops the current application and launches the newly selected one. Although Palm OS applications are event-driven, they may perform work outside of the event loop in response to other system requests. For example, if the user uses the find facility to search the device for a particular word, each application is launched and asked to search its databases for a record containing data that matches.

Palm OS applications are compiled into PRC files (Palm Resource file) and then downloaded to the handheld. The same PRC runs on all Palm branded devices as well as all licensee devices such as Handspring, Symbol, or Sony. Some devices do have individual characteristics that can be coded to.

Development environments are available for creating Palm OS applications in a number of different languages such as C, C++, Visual BASIC, or Java. You choose a development environment based on the programming language you want to use, but be aware of the consequences of the choice you make. The most commonly used development environments use standard C as the programming language, and add-ons are available to allow you to use C++ frameworks as well. With C or C++ applications, the Palm OS provides much of the functionality that applications need for memory management, string manipulation, drawing to the screen, and so on. Linking to standard C or C++ libraries is not necessary. This keeps your application compact and efficient. The development environments for Visual BASIC, Java, and even some of the C-based development environments require a runtime engine to be present. Some of these environments require the engine be present on the device, and others compile runtime elements into the application. In either case, the resulting code base is not as compact as with the C-based applications. However, the runtime engines are typically free to the user, and the development tool may very well add enough benefit to make the increase in code size worthwhile.

If you choose C or C++, you also need the free SDK that Palm provides. In addition to providing the necessary header files for C development, the Palm OS SDK also includes documentation and a number of useful tools.

5.1.1.PDA Models
Click Here for PDA Models

5.2.WinCE
Microsoft® Windows® CE is an open, scalable, 32-bit operating system that is designed to meet the needs of a broad range of intelligent devices, from enterprise tools such as industrial controllers, communications hubs, and point-of-sale terminals to consumer products such as cameras, telephones, and home entertainment devices. A typical Windows CE-based embedded system is targeted for a specific use, an often run disconnected from other computers, and requires an operating system that has a small footprint and a built-in deterministic response to interrupts.

Windows CE offers the application developer the familiar environment of the Microsoft Win32® application programming interface (API),

• ActiveX controls
• Message queuing (MSMQ)
• Component Object Model (COM) interfaces
• Active Template Library (ATL)
• Microsoft Foundation Classes (MFC) Library.

ActiveSync provides easy connectivity between the desktop and the embedded device, whether by serial connection, infrared port, or network cable. Windows CE provides built-in support for multimedia (including DirectX), communications (TCP/IP, SNMP, TAPI, and more), and security. A variety of integrated applications, including Pocket Internet Explorer, Inbox client for Pocket Outlook, and Pocket Word expose objects that allow you to extend and customize the existing system, as well as extend the functionality of your own application.

Windows CE is the modular real-time embedded operating system for small footprint and mobile 32-bit intelligent and connected devices. Windows CE combines Windows compatibility and advanced application services with support for multiple CPU architectures and built-in networking and communications options to deliver a rich, scalable open foundation for building a wide variety of products. Windows CE powers consumer electronic devices, Web terminals, Internet access appliances, specialized industrial controllers, mobile data acquisition handhelds, and embedded communication devices. This highly modular platform allows developers to flexibly and reliably build the new generation of small footprint and mobile 32-bit devices that integrate seamlessly with Windows and the Internet.

5.2.1.PDA Models