Symbian OS is an open operating system, designed for mobile devices, with associated libraries, user interface frameworks and reference implementations of common tools, produced by Symbian Ltd. It is a descendant of Psion's EPOC and runs exclusively on ARM processors.
On 24 June 1998, Symbian Ltd. was formed as a partnership between Ericsson, Nokia, Motorola and Psion, to exploit the convergence between PDAs and mobile phones. Symbian was previously owned by Nokia (56.3%), Ericsson (15.6%), Sony Ericsson (13.1%), Panasonic (10.5%) and Samsung (4.5%). Ten years to the day later, on 24 June 2008, Nokia announced that they intended to acquire all shares that they did not already own. The acquisition was of €264 million, or $410 million.
Symbian OS was built to follow three design rules: the integrity and security of user data is paramount, user time must not be wasted, and all resources are scarce. This led to a continuation of the use of servers, a microkernel, a request and callback approach to all services, an absolute division of user interfaces from system or application services, reuse and openness, extensibility, and robust management and resource recovery to support extended always-on operation. For hardware the OS is optimised for low-power battery-based devices and for ROM-based systems (e.g. features like XIP and re-entrancy in shared libraries). Applications, and the OS, follow an object-oriented design, MVC.
Later OS iterations diluted this approach in response to market demands, notably the introduction of a real-time kernel and a platform security model in versions 8 and 9.
There is a strong emphasis on conserving resources, using Symbian-specific programming idioms such as descriptors and a cleanup stack. There are similar techniques for conserving disk space (though the disks on Symbian devices are usually flash memory). Furthermore, all Symbian OS programming is event-based, and the CPU is switched off when applications are not directly dealing with an event. This is achieved through a programming idiom called active objects. Similarly the OS approach to threads vs. processes is driven by reducing overheads.
Symbian OS EKA2 supports sufficiently-fast real-time response such that it is possible to build a single-core phone around it—that is, a phone in which a single processor core executes both the user applications and the signalling stack. This is a feature which is not available in Linux. This has allowed SymbianOS EKA2 phones to become smaller, cheaper and more power efficient.
The Base Services Layer is the lowest level reachable by user-side operations; it includes the File Server and User Library, the Plug-In Framework which manages all plug-ins, Store, Central Repository, DBMS, and cryptographic services. It also includes the Text Window Server and the Text Shell, the two basic services from which a completely functional port can be created without the need for any higher layer services.
Symbian OS has a microkernel architecture, which means that the minimum necessary is within the kernel to improve robustness, availability, and responsiveness. It contains a scheduler, memory management, and device drivers, but other services like networking, telephony, or filesystem support are placed in the OS Services Layer or Base Services Layer. The inclusion of device drivers means the kernel is not a true microkernel. The EKA2 real-time kernel has been termed a nanokernel, containing only the most basic primitives and supporting an extended kernel to implement any other abstractions.
Symbian OS is designed to emphasize compatibility with other devices, especially removable media file systems. Early development of EPOC led to adopting FAT as the internal file system and this remains in the Symbian OS but an object-oriented persistence model has been placed over the underlying FAT, providing a POSIX-style interface and a streaming model. The internal data formats rely on using the same API that create the data to run all file manipulations - this has created the problems of data-dependence and associated difficulties with changes and data migration.
There is a large networking and communication subsystem, which has three main servers: ETEL (EPOC telephony), ESOCK (EPOC sockets) and C32 (responsible for serial communication). Each of these has a plug-in scheme. For example ESOCK allows different ".PRT" protocol modules, implementing different types of networking protocol scheme. The subsystem also contains code that pertains to short-range communication links, such as Bluetooth, IrDA and USB.
There is also a large volume of user interface (UI) Code. Only the base classes and substructure are contained in Symbian OS, while most of the actual user interfaces are maintained by third parties. This component is known as UIKON. The OS also contains the graphics, text layout, and font rendering libraries.
All Symbian applications are built up from three classes defined by the application architecture: an application class, a document class, and an application user interface class. These classes create the fundamental application behaviour. The remaining required functions, the application view, data model, and data interface, are created independently and interact solely through their APIs with the other classes. UIQ and S60 both extend this approach, in two different ways.
Many other things do not yet fit into this model – for example, SyncML, Java ME providing another set of APIs on top of most of the OS and multimedia. Many of these are frameworks, and vendors are expected to supply plug-ins to these frameworks from third parties (for example, Helix player for multimedia codecs). This has the advantage that the APIs to such areas of functionality are the same on many phone models, and that vendors get a lot of flexibility. But it means that phone vendors need to do a great deal of integration work to make a Symbian OS phone.
Symbian OS device manufacturers also get supplied with an example user-interface layer called "TechView". It provides a basis to start customisation and is also the environment in which much Symbian OS test code and example code runs. It is very similar to the user interface from a Psion Series 5 personal organiser, so it is not used for any given phone user interface.
The first 'open' Symbian OS phone, the Nokia 9210 Communicator, was released in June 2001. Bluetooth support added. Almost 500,000 Symbian phones were shipped in 2001, rising to 2.1 million the following year.
Development of different UIs was made generic with a "reference design strategy" for either 'smartphone' or 'communicator' devices, subdivided further into keyboard- or tablet-based designs. Two reference UIs (DFRDs or Device Family Reference Designs) were shipped - Quartz and Crystal. The former was merged with Ericsson's 'Ronneby' design and became the basis for the UIQ interface, the latter reached the market as the Nokia Series 80 UI.
Later DFRDs were Sapphire, Ruby, and Emerald. Only Sapphire came to market, evolving into the Pearl DFRD and finally the Nokia Series 60 UI, a keypad-based 'square' UI for the first true smartphones. The first one of them was the Nokia 7650 smartphone (featuring Symbian OS 6.1), which was also the first with a built-in camera, with VGA (0.3 Mpx = 640*480) resolution.
Despite these efforts to be generic the UI was clearly split between competing companies, Crystal or Sapphire was Nokia, Quartz was Ericsson. DFRD was abandoned by Symbian in late 2002, as part of an active retreat from UI development in favour of 'headless' delivery. Pearl was given to Nokia, Quartz development was spun-off as UIQ Technology AB, and work with Japanese firms was quickly folded into the MOAP standard.
One million Symbian phones were shipped in Q1 2003, with the rate increasing to one million a month by the end of 2003.
Symbian OS 7.0s was a version of 7.0 special adapted to have greater backwards compatibility with Symbian OS 6.x, partly for compatibility between the Communicator 9500 and its predecessor the Communicator 9210.
In 2004, Psion sold its stake in Symbian. The same year, the first worm for mobile phones using Symbian OS, Cabir, was developed, which used Bluetooth to spread itself to nearby phones. See Cabir and Symbian OS threats.
Symbian OS has generally maintained reasonable binary compatibility. In theory the OS was BC from ER1-ER5, then from 6.0 to 8.1b. Substantial changes were needed for 9.0, related to tools and security, but this should be a one-off event. The move from requiring ARMv4 to requiring ARMv5 did not break backwards compatibility.
A Symbian developer proclaims that porting from Symbian 8.x to Symbian 9.x is a more daunting process than Symbian says.
Support for Bluetooth 2.0 (was 1.2)
Symbian has announced PIPS (PIPS Is POSIX on Symbian) which may increase the number of open source projects written for Symbian 9.1.
However, with a view that the average mobile phone user shouldn't have to worry about security, Symbian OS 9.x has adopted a capability model. Installed software will theoretically be unable to do damaging things (such as costing the user money by sending network data) without being digitally signed – thus making it traceable. Commercial developers who can afford the cost can apply to have their software signed via the Symbian Signed program. Currently, developers also have the option of self-signing their programs. However, the set of available features is smaller, and certain operators have opted on fully disabling certificates other than the Symbian Signed certificates.
Some other hostile programs are listed below, but all of them still require the input of the user to run.
Symbian OS 9 uses a new ABI and so requires a new compiler – a choice of compilers is available including a new version of GCC (see external links below). In terms of SDKs, UIQ Technology now provides a simplified framework so that the single UIQ SDK forms the basis for developing on all UIQ 3 devices, such as the Sony Ericsson P990 and Sony Ericsson M600.
Unfortunately, Symbian C++ programming has a steep learning curve, as Symbian requires the use of special techniques such as descriptors and the cleanup stack. This can make even relatively simple programs harder to implement than in other environments. Moreover, it is questionable whether Symbian's techniques e.g. the memory management paradigm are actually so beneficial. It is possible that the techniques, developed for the much more restricted mobile hardware of the 1990s, do cause unnecessary complexity in source code; programmers are required to concentrate on bug-prone low-level routines instead of truly application-specific features. It is difficult, however, to make a move towards a more high-level and modern programming paradigm in Symbian, because the platform is so tightly bound to semi-obsolete thinking models about mobile software development.
Symbian C++ programming is commonly done with an IDE. For previous versions of Symbian OS, the commercial IDE CodeWarrior for Symbian OS was favoured. The CodeWarrior tools were replaced during 2006 by Carbide.c++, an Eclipse-based IDE developed by Nokia. Carbide.c++ is offered in 4 different versions: Express, Developer, Professional, and OEM, with increasing levels of capability. Full featured software can be created and released with the Express edition, which is free. Features such as UI design, crash debugging etc. are available in the other charged for editions. Microsoft Visual Studio 2003 and 2005 are also supported through the Carbide.vs plugin.
Symbian OS's flavour of C++ is very specialised. However, many Symbian OS devices can also be programmed in OPL, Python, Visual Basic, Simkin, and Perl – together with the Java ME and PersonalJava flavours of Java.
Visual Basic programmers can use NS Basic to develop apps for S60 3rd Edition and UIQ 3 devices.
In the past, Visual Basic, VB.NET, and C# development for Symbian were possible through AppForge Crossfire, a plugin for Microsoft Visual Studio. March 13, 2007 AppForge ceased operations, Oracle purchased the intellectual property, but announced that they do not plan to sell or provide support for former AppForge products.
There is also a version of a Borland IDE for Symbian OS. Symbian OS development is also possible on Linux and Mac OS X using tools and techniques developed by the community, partly enabled by Symbian releasing the source code for key tools. A plugin that allows development of Symbian OS applications in Apple's Xcode IDE for Mac OS X is available.
Once developed, Symbian OS applications need to find a route to customers' mobile phones. They are packaged in SIS files which may be installed over-the-air, via PC connect or in some cases via Bluetooth or memory cards. An alternative is to partner with a phone manufacturer to have the software included on the phone itself. The SIS file route is more difficult for Symbian OS 9.x, because any application wishing to have any capabilities beyond the bare minimum must be signed via the Symbian Signed program. There are however various hacks, which allow installing unsigned programs with any capabilities to Symbian OS 9.x.
Introduction of the Symbian Signed system in which application developers need to pay in order to use some of the more attractive smartphone features (as contrasted to platforms like Palm OS and Windows Mobile) is making it an increasingly unpopular platform for Open Source projects, independent developers and small startups. This situation is worsened by the fragmentation of user interface systems (UIQ vs S60 vs MOAP), meaning that developers need to build and maintain multiple incompatible versions of their software if they want to target multiple devices which use the same underlying Symbian OS version.
Java ME applications for Symbian OS are developed using standard techniques and tools such as the Sun Java Wireless Toolkit (formerly the J2ME Wireless Toolkit). They are packaged as JAR (and possibly JAD) files. Both CLDC and CDC applications can be created with NetBeans. Other tools include SuperWaba, which can be used to build Symbian 7.0 and 7.0s programs using Java.
Nokia S60 phones can also run python scripts when the interpreter is installed, with a custom made API that allows for Bluetooth support and such. There is also an interactive console to allow the user to write python scripts directly from the phone.
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