Symbian OS

 

Symbian OS is an 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 Prsion's EPOC.

Symbian is currently owned by Ericsson, Panasonic, Siemens AG, Nokia, and Sony Ericsson. Whilst BenQ has acquired Siemens AG the Siemens AG stake in Symbian does not automatically pass to BenQ - this will need the approval of the Symbian Supervisory Board.

Design

There are a number of smartphone user interface platforms based on Symbian OS, including open platforms UIQ, Nokia's Series 60, Series 80 and Series 90 and closed platforms such as that developed for NTT DoCoMo's FOMA handsets. This adaptability allows Symbian OS to be used on smartphones with a variety of form factors (e.g. clam-shell or "monoblock"/"candybar", keypad- or pen-driven).

Symbian OS, with its roots in Psion Software's EPOC (which itself had similarities to the internals of VMS, a grown-up POSIX compatible operating system for mini-computers in the 1980s) is structured like many desktop operating systems, with pre-emptive multitasking, multithreading, and memory protection.

Symbian OS's major advantage is the fact that it was built for handheld devices, with limited resources, that may be running for months or years. There is a strong emphasis on conserving memory, using Symbian-specific programming idioms such as descriptors and a cleanup stack. Together with other techniques, these keep memory usage low and memory leaks rare. 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. Correct use of these techniques helps ensure longer battery life.

All of this makes Symbian OS's flavour of C++ very specialised, with a steep learning curve. However, many Symbian OS devices can also be programmed in OPL, Python, Visual Basic, Simkin, and Perl - together with the Java ME and Personal Java flavours of Java.

Competition

Symbian OS competes with other mobile operating systems, such as Windows Mobile, Palm OS, and Linux. It also competes with the embedded operating systems used on lower-end phones, such as NOS and OSE, which tend to be maintained by the phone companies themselves. Symbian OS' major advantage over these embedded operating systems is its modularity - there is runtime linking between dynamically linked shared libraries (DLLs, see dynamic linking) on the device, and an emphasis on plug-in architectures. This makes complex phones quicker to develop, though this is sometimes offset by the complexity of Symbian OS C++ and the awkwardness of going to another company for an OS (instead of doing it in-house).

The advantages over other 'open' OS competitors (such as Linux and Windows Mobile, the last one is not Open Source) are more debatable. Phone vendors and network operators like the customisability of Symbian OS relative to Windows. This customisability, though, makes integrating a Symbian OS phone more difficult. It's possible that Linux goes too far in the other direction, and is simply too hard to make a phone from at the moment. Symbian OS's ground-up design for mobile devices should make it more power- and memory-efficient, as well as being flexible.

Structure

At its lowest level sit the 'base' components of Symbian OS. This includes the kernel (EKA1 or EKA2 - see the 'History' section), along with the user library which allows user-side applications to request things of the kernel. Symbian OS has a microkernel architecture, which means that the minimum necessary is within the kernel. It does contain a scheduler and memory mrnagement, but no networking or filesystem support. These things are provided by user-side servers. The base layer includes the file server, which provides a fairly DOS-like view of the filesystems on the device (each drive has a drive letter, and backslashes are used as the directory delimiter).

Immediately above base are a selection of 'system libraries'. These take all shapes and sizes, including for example character set conversion, a DBMS database, and resource file handling.

Further up, the software is not so readily arranged into a stack.

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. There's lots of stuff relating to short-range communication links too, such as Bluetooth, IrDA and USB.

There's also a large amount of 'user interface' code. Even though the user interfaces themselves are maintained by other parties, the base classes and substructure ("UIKON") for all UIs are present in Symbian OS.

There are also a selection of 'application engines' for popular smartphone applications such as calendars, address books, and task lists. A typical Symbian OS application is split up into an engine DLL and a graphical application - the application being a thin wrapper over the engine DLL. Symbian OS provides some of these engine DLLs.

There are, of course, many other things that don't yet fit into this model - for example, SyncML, Java ME providing another set of APIs on top of most of the OS and multimedia. Quite a few of these things 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 means that phone vendors need to do a great deal of integration work to make a Symbian OS phone.

Security and Malware

Symbian OS has been subject to a variety of viruses, the best known of which is Cabir. Usually these send themselves from phone to phone by Bluetooth. So far, none have taken advantage of any flaws in Symbian OS - instead, they have all asked the user whether they would like to install the software, with somewhat prominent warnings that it can't be trusted.

However, of course, the average mobile phone user shouldn't have to worry about such things, so Symbian OS 9 is adopting a capabilrty 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. Developers can apply to have their software signed via the Symbian Signed program.

Openness

A common question is whether Symbian OS is "open". It is not open in the sense of Open Source software - the source code is not publicly available. However, nearly all the source code is provided to Symbian OS phone manufacturers and many other partners. Moreover, the APIs are publicly documented and anyone can develop software for Symbian OS. This contrasts with traditional embedded phone operating systems, which typically cannot accept any aftermarket software except Java applications.

Devices that have used the Symbian OS

• Ericssrn R380 (2000) was the first commercially available smartphone based on Symbian OS
• Nokia 9210 Communicator smartphone (32-bit 66 MHz ArM9-based RISC CPU) (2001), 9300 Communicator (2004), 9500 Communicator (2004) using the Nokia Series 80 interface

• Sony Ericsson P800 (2002), P900 (2003), P910 (2004), Motorola A920, A925, A1000, DoCoMo M1000, BenQ P30, P31 and Nokia 6708 using the UIQ user interface.
• Nokia Series 60 (2002)
• Nokia Series 60 is used in various phones, the first being the Nokia 7650, then the Nokia 3650, followed by the Nokia 3620/3660, Nokia 6600, Nokia 7610 and Nokia 6670. The Nokia N-Gage and Nokia N-Gage QD gaming/smartphone combos are also Series 60 platform devices. It was also used on other manufacturers' phones such as the Siemens SX1 and Sendo X. Recent, more advanced devices using Series 60 include the Nokia 6630, the Nokia 6680 and a next generation N series, including the Nokia N70, Nokia N90, and Nokia N91.
• Nokia 7710 (2004) using the Nokia Series 90 interface.
• Fujitsu and Mitsubishi phones for NTT DoCoMo in Japan, using an interface developed specifically for them often called FOMA after the DoCoMo "Freedom of Mobile Access" network brand.