The Symbian OS was designed specifically for mobile devices. It has a very small memory footprint and low power consumption. This is very important, as users do not want to recharge their phone daily and to allow to run on small devices with limited memory. Unlike other proprietary operating systems, it is an open OS, enabling third party developers to write and install applications independently from the device manufacturers.

An extensive C++ API is provided which allows access to services such as telephony and messaging, in addition to basic OS functionality. Some devices that run Symbian may not be switched off for years, therefore the OS was designed so applications could run for years without loosing the user data. Also the OS can run on more than one hardware platform, so it can be used on a variety of device types including those touch screens and those with pens or keyboards.

Symbian OS is the current name of the operating system, but when it was initially released it was known as ‘EPOC’. The name EPOC was used for some time and will still be found in class/file names and in older documentation. The name EPOC is still used to refer to the kernel.

Symbian OS is highly optimized, heavily asynchronous, pre-emptive, multitasking operating system. It was redesigned from scratch in 1994 as a 32bit OS. Most of the code is in C++. Very little code exists in C or assembly. The OS supports the client-server architecture. Symbian OS provides a class framework and a suite of organising and communicating applications.

All the system services are run from ROM directly. The user applications reside in RAM. Multi-threading and context switch are not encouraged at the user application level.

We’ll look at the various layers of the Symbian OS and the architecture of the Symbian OS in the upcoming articles.