Symbian

Contents

1 Design

2 Competition

3 Structure

4 History

5 Security and Malware

6 Openness

7 Devices that have used the Symbian OS

8 Developing on Symbian OS

9 External links

Design

There are a number of smartphone user interface platforms based on Symbian OS, including open platforms UIQ, Nokia's Series 60 and Series 80, 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 J2ME 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 management, 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 delimeter).

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 fit into this model - for example, SyncML, J2ME 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.

History

In 1980, Psion Software was founded by David Potter.

EPOC16. Psion released several Series 3 devices from 1991 to 1998 which used the EPOC16 OS, also known as SIBO.

EPOC