The paper aims to outline those ICL 2900 hardware features that support system software. The treatment broadly is in terms of the instruction set and other hardware features. 2900 architecture provides for concurrent execution of independent in virtual machines, so that the processes are protected from mutual interference. The protection arrangements are outlined together with ways of addressing the store, for which several kinds of descriptors may be used. There are both visible and invisible hardware registers; access to the latter is privileged via a so called image store addressing mechanism. The arrangements for handling interrupts and entering procedures are outlines. Slave stores are provided for reducing store access demands for frequently accessed items. Peripheral transfers are via autonomous and asynchronous controllers activated by processes operating within a central processor. In conclusion some of the main considerations influencing design decisions are reviewed.