Abstract: Inhibit means prevents a store-in-cache (SIC) from requesting or receiving any line fetch from MS when a clear line (CL) command is issued by a CPU to main storage (MS).Two CPU modes are provided: (1) an initial storage validation mode and (2) an instruction processing mode. The system operator controls the first mode so that a CPU can execute the CL command during system initialization without any prior data fetch from MS. In the second mode, the CL command is executed as a component of a program instruction fetched from MS that can clear a block in main storage.In a multiprocessor (MP), the CL command by any CPU requests a line store of pad data into an addressed line in MS only after each other SIC copy directory is searched and any found conflicting line is invalidated. Line castout to MS is prohibited for a conflicting line found in a cache by the CS command, which would have been a normal operation for other types of CPU commands.

Abstract: A multiprocessor (MP) system is described having central processors (CPs) in which each CP has a store-in-cache (SIC) with an associated processor directory (PD). Each PD has a plurality of line entries which define the content of corresponding line positions in the associated SIC. Each line entry has an associated data shareability control bit, designated EX, which may be set to a one or zero state to indicate, respectively, the exclusive (EX) or readonly (RO) state of the associated line. An exclusive line is not shareable, but a readonly line is shareable i.e. may exist validly in more than one SIC in the MP. Any CP in the MP can request data in an EX state from its SIC, which data may or may not be found in its SIC or in another CP's SIC.

Abstract: The disclosure provides a storage protection (SP) array in each of two system controllers (SCs) in a multiprocessing system which has a shared main storage containing a plurality of basic storage modules (BSMs). The BSMs may be operated with block and page interleaved addresses. Each block in main storage is assigned a key-in-storage having an entry in one of the two arrays.A cross-interrogate (XI) bus connects between the SCs. Using the XI bus, each processor request is sent to an SP address register in every SP array.Each array is divided into a plurality of equal groups. Each group has a range identifier register and a comparator. The range identifier register is loaded with a value which controls the range of main storage addresses to which the group is assigned. All of the comparators in each array are connected to a high-order part of the SP address register for the array.