Abstract: Each process in a multi-process computing system using so-called capabilities may have associated with it a process dumpstack protected by the capability mechanism. The functions of this dumpstack are (i) to provide the state of the process at the point at which it was suspended and (ii) to stack (or nest) information relating to the invoked procedures (i.e. sub-routines) of the process. Thus there is a fixed sized portion containing principally the machine registers, the indicators and the watchdog timer values and a variable sized portion containing information related to each nested procedure. Each stack link is of fixed size and contains three items:- relativized instruction address, the code block capability and process capability pointer list block capability.

Abstract: The use of protected capability registers to hold the physical base and limit addresses and access rights for a block of memory and the way in which such registers are loaded using System Capability Tables and reserved segment pointer tables is well known in the prior art. In the present invention the normal capability load instruction has been enhanced in four major ways:(a) allowing additional capability classes to be handled(b) instituting a "load on use" facility(c) instituting capability propagation control and(d) implementing access reduction facilitiesThe capability classes comprise (i) system store, (ii) system resource, (iii) local store and (iv) passive capability. The "load on use" facility speeds up the load capability instruction and the change process instruction.

Abstract: In a multi-processor system of the type in which each processor is provided with its own unique bus which has an addressing system organized in such a manner that all store locations and peripheral equipments are addressed as part of a comprehensive single addressing system. Each address comprises a module number and an offset address. Each module in the system includes a module number comparator which detects the presence of its module address on a CPU bus and allows the offset address to be active within that module. The invention provides for the incorporation of similar mechanisms within a CPU allowing the CPU to address its own internal registers in an identical manner to its normal bus addressing mode. In addition the offset address includes a "bit portion address" which selects a mask which is used when performing the required internal register operation.