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 OS Releases 13. The Series 5 device, released in 1997, used the first iterations of the EPOC32 OS.

EPOC Release 4. Oregon Osaris and Geofox 1 were released using ER4.

In 1998, Symbian Ltd. was formed as a partnership between Ericsson, Nokia, Motorola and Psion, to explore the convergence between PDAs and mobile phones.

EPOC Release 5 a.k.a. Symbian OS v5. Psion Series 5mx, Series 7, Psion Revo, Psion Netbook, netPad, Ericsson MC218 were released in 1999 using ER5.

ER5u a.k.a. Symbian OS v5.1. u Unicode. The first phone, the Ericsson R380 was released using ER5u in 2000. It was not an 'open' phone - software could not be installed. Notably, a number of never released Psion prototypes for next generation PDAs, including a Bluetooth Revo successor codenamed Conan were using ER5u.

Symbian OS v6.0 and v6.1. Sometimes called ER6. The first 'open' Symbian OS phone, the Nokia 9210, was released on 6.0.

Symbian OS v7.0 and v7.0s. First shipped in 2003. This is an important Symbian release which appeared with all contemporary user interfaces including UIQ (Sony Ericsson P800, P900, P910, Motorola A925, A1000), Series 80 (Nokia 9300, 9500), Series 90 (Nokia 7710), Series 60 (Nokia 6600, 7310) as well as several FOMA phones in Japan.

In 2004, Psion sold its stake in Symbian.

Also in 2004, 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 v8.0. First shipped in 2004, one of its advantages would have been a choice of two different kernels (EKA1 or EKA2). However, the EKA2 kernel version did not ship until SymbianOS v8.1b. The kernels behave more or less identically from user-side, but are internally very different. EKA1 was chosen by some manufacturers to maintain compatibility with old device drivers, whilst EKA2 offered advantages such as a hard real-time capability. v8.0b was deproductized in 2003.

Symbian OS v8.1. Basically a cleaned-up version of 8.0, this was available in 8.1a and 8.1b versions, with EKA1 and EKA2 kernels respectively. The 8.1b version, with EKA2's single-chip phone support but no additional security layer, was popular among Japanese phone companies desiring the realtime support but not allowing open application installation.

Symbian OS v9.0. This version was used for internal

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