In March 1999, RISCOS Ltd obtained exclusive rights to develop and sell RISC OS 4 for the desktop market from Element 14.

A few weeks later Pace purchased Acorn's Cambridge headquarters and staff for £200,000 and then continued to develop its own, in-house version of RISC OS, primarily for set-top boxes and other embedded devices.

At the time of the company's formation, it was noted that having access to the source code could facilitate removal of the OS's dependence on Acorn's proprietary chips.

[9] RISCOS Ltd completed work on RISC OS 4 and in July 1999 it was released as an upgrade for existing machines, priced at £120.

In the same year, RISCOS Ltd agreed to produce a fully 32-bit-compatible version of RISC OS Adjust for Advantage Six's A9home product.

Significant portability, stability and internal structure improvements, including full 26/32-bit neutrality, have laid the foundations for the company's future releases, all of which will be based on version 6.

In July 2003, Castle bought all technology rights to RISC OS from Pace in an attempt to legalise the situation.