Windows CE is optimized for devices that have minimal storage—a Windows CE kernel may run in under a megabyte of memory. Devices are often configured without disk storage, and may be configured as a “closed” system that does not allow for end-user extension (for instance, it can be burned into ROM). Windows CE conforms to the definition of a real-time operating system, with a deterministic interrupt latency. From version 3 and onward, the system supports 256 priority levels[4] and uses priority inheritance for dealing with priority inversion. The fundamental unit of execution is the thread. This helps to simplify the interface and improve execution time.
Microsoft has stated that the ‘CE’ is not an intentional initialism, but many people believe CE stands for ‘Consumer Electronics’ or ‘Compact Edition’. Microsoft says it implies a number of Windows CE design precepts, including “Compact, Connectable, Compatible, Companion, and Efficient.”[5] The first version, known during development under the code name “Pegasus”, featured a Windows-like GUI and a number of Microsoft's popular applications, all trimmed down for smaller storage, memory, and speed of the palmtops of the day.
Since then, Windows CE has evolved into a component-based, embedded, real-time operating system. It is no longer targeted solely at hand-held computers[6]. Many platforms have been based on the core Windows CE operating system, including Microsoft's AutoPC, Pocket PC 2000, Pocket PC 2002, Windows Mobile 2003, Windows Mobile 2003 SE, Windows Mobile 5.0, Windows Mobile 6, Smartphone 2002, Smartphone 2003, Portable Media Center and many industrial devices and embedded systems. Windows CE even powered select games for the Dreamcast, was the operating system of the Gizmondo handheld, and can partially run on modified Xbox game consoles.
A distinctive feature of Windows CE compared to other Microsoft operating systems is that large parts of it are offered in source code form. First, source code was offered to several vendors, so they could adjust it to their hardware. Then products like Platform Builder (an integrated environment for Windows CE OS image creation and integration, or customized operating system designs based on CE) offered several components in source code form to the general public. However, a number of core components that do not need adaptation to specific hardware environments (other than the CPU family) are still distributed in binary only form.
Relationship to Windows Mobile, Pocket PC, and SmartPhone
Often Windows CE, Windows Mobile, and Pocket PC are used interchangeably - in part due to their common origin. This practice is not entirely accurate. Windows CE is a modular/componentized operating system that serves as the foundation of several classes of devices. Some of these modules provide subsets of other components' features (e.g. varying levels of windowing support; DCOM vs COM), others which are separate (Bitmap or TrueType font support), and others which add additional features to another component. One can buy a kit (the Platform Builder) which contains all these components and the tools with which to develop a custom platform. Applications such as Excel Mobile/Pocket Excel are not part of this kit. The older Handheld PC version of Pocket Word and several other older applications are included as samples, however.
Windows Mobile is best described as a subset of platforms based on a Windows CE underpinning. Currently, Pocket PC (now called Windows Mobile Classic), SmartPhone (Windows Mobile Standard), and PocketPC Phone Edition (Windows Mobile Professional) are the three main platforms under the Windows Mobile umbrella. Each platform utilizes different components of Windows CE, as well as supplemental features and applications suited for their respective devices.
Pocket PC and Windows Mobile is a Microsoft-defined custom platform for general PDA use, and consists of a Microsoft-defined set of minimum profiles (Professional Edition, Premium Edition) of software and hardware that is supported. The rules for manufacturing a Pocket PC device are stricter than those for producing a custom Windows CE-based platform. The defining characteristics of the Pocket PC are the digitizer as the primary human interface device and its extremely portable size.
The SmartPhone platform is a feature rich OS and interface for cellular phone handsets. SmartPhone offers productivity features to business users, such as email, as well as multimedia capabilities for consumers. The SmartPhone interface relies heavily on joystick navigation and PhonePad input. Devices running SmartPhone do not include a touchscreen interface. SmartPhone devices generally resemble other cellular handset form factors, whereas most Phone Edition devices use a PDA form factor with a larger display.
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