Abstract: A multiprocessor computer system includes a main memory and a plurality of central processing units (CPU's) which are connected to share main memory via a common bus network. Each CPU has instruction and data cache units, each organized on a page basis for complete operating compatibility with user processes. Each cache unit includes a number of content addressable memories (CAM's) and directly addressable memories (RAM's) organized to combine associative and direct mapping of data or instructions on a page basis. An input CAM in response to a CPU address provides a cache address which includes a page level number for identifying where all of the required information resides in the other memories for processing requests relating to the page. This organization permits the processing of either virtual or physical addresses with improved speed and reduced complexity and the ability to detect and eliminate both consistency and synonym problems.

Abstract: A least recently used replacement level generator is constructed to include n number of register stages connected in tandem. A comparison circuit associated with each stage except the last stage compare the contents of that stage with an input level value which is to be loaded into the input stage. In the absence of an identical comparison, each stage generates a shift enable signal which is passed on to the next succeeding stage. An identical comparison inhibits the generation of the shift enable signal. Therefore, when a clock signal is applied to the device, register stages, in the presence of a control signal, cause the input level to be loaded into the input stage while the level contents of the register stages are simultaneously shifted through successive stages including the register stage whose contents are identical to the input level under the control of the shift enable signal.

Abstract: A cache memory unit is constructed to have a two-stage pipeline shareable by a plurality of sources which include two independently operated central processing units (CPUs). Apparatus included within the cache memory unit operates to allocate alternate time slots to the two CPUs which offset their operations by a pipeline stage. This permits one pipeline stage of the cache memory unit to perform a directory search for one CPU while the other pipeline stage performs a data buffer read for the other CPU. Each CPU is programmed to use less than all of the time slots allocated to it. Thus, the processing units operate conflict-free while pipeline stages are freed up for processing requests from other sources, such as replacement data from main memory or cache updates.

Abstract: Apparatus that provides interrupt operation in a central processor based system wherein internal subsystems are operated via addresses generated by a next address generator in the processor and sent to control stores associated with each subsystem to thereby read out firmware instructions which are used by a controller in each subsystem to control the operations of same. When a special condition is detected in ones of the subsystems a trap signal is sent to the next address generator which responds by generating a microinstruction address to the subsystem that generated the trap signal. The subsystem responds to the microinstruction to read out a register, the contents of which indicate the status of processing in the subsystem including the special condition.

Abstract: A method and apparatus for a microinstruction controlled unit to recover from a read error in reading microinstructions from a control store. The method provides for the overlapping of the execution of a current microinstruction while the next microinstruction is being addressed and read from the control store. Execution of the current microinstruction is begun before it is known whether or not it was read without error. The apparatus provides for aborting the execution of the current microinstruction with the read error and the next microinstruction. During the aborted execution of the next microinstruction, the current microinstruction is reread from the control store and then executed while the next microinstruction is being reread. The execution of microinstructions is aborted in a manner that does not alter the state of the microinstruction controlled unit beyond the point that would inhibit the re-execution of the aborted microinstructions.

Abstract: In a data processing system, a central subsystem includes a plurality of special purpose processing units with one of the processing units serving as a control processing unit within a central subsystem. The processing units are coupled to a common subsystem bus for the transfer of data, control information, and address information within the central subsystem. Access to the subsystem bus is allocated by a bus control unit which also interfaces the central subsystem with other processing units such as a system memory or system I/O devices that are included in the data processing system.

Abstract: The performance of a scientific ADD instruction is improved by storing the mantissas of both operands in each of two random access memories, selecting the mantissa with the smaller exponent, shifting that mantissa and performing the ADD operation of adding the mantissas in one machine cycle.

Abstract: Mantissa results of floating point operations are truncated to words of 24 bits each by storing the 64 bit mantissa result in a first address location of a random access memory, and storing binary ZEROs in the 48 least significant bit positions of a second address location of the random access memory. The mantissa result is truncated by addressing the high order 24 bits at the first address location and the 48 binary ZEROs at the second address location.

Abstract: If the firmware calls for an operand rounding operation, apparatus in the Scientific Instruction Processor (SIP) tests the bit to the right of the low order bit of the normalized operand to determine if a rounding cycle is required. If the operand requires a normalization cycle or a mantissa overflow correction cycle, the rounding operation is performed in those cycles.

Abstract: A word oriented data processing system includes a plurality of system units all connected in common to a system bus. Included are a central processor unit (CPU), a memory system and a high speed buffer or cache system. The cache system is also coupled to the CPU. The cache includes an address directory and a data store with each address location of directory addressing its respective word in data store. The CPU requests a word of cache by sending a memory request to cache which includes a memory address location. If the requested word is stored in the data store, then it is sent to the CPU. If the word is not stored in cache, the cache requests the word of memory. When the cache receives the word from memory, the word is sent to the CPU and also stored in the data store.

Abstract: A first in-first out buffer memory coupled to a system bus receives all information transferred over the bus. Logic associated with the buffer memory tests if the information received is intended to update main memory or is in response to a cache request. The information is written into cache if the main memory address location is stored in a cache directory. The information received in response to a cache request is stored in a cache data buffer. Other information is discarded.

Abstract: In a data processing system which includes a plurality of system units such as a central processing unit (CPU), main memory, and cache memory all connected in common to a system bus and communicating with each other via the system bus, and also having a private CPU-cache memory interface for permitting direct cache memory read access by the CPU, a multi-configurable cache store control unit for permitting cache memory to operate in any of the following word modes:1. Single pull banked;2. Double pull banked;3. Single pull interleaved;4. Double pull interleaved.The number of words read is a function of the main store configuration and the amount of memory interference from I/O controllers and other subsystems. The number ranges from one to four under the various conditions.

Abstract: During system initialization, a cache is completely loaded with valid information from main memory. The directory and data buffer are organized in levels of memory locations. Each level of the directory and data buffer is loaded in turn from main memory. Round Robin apparatus, which is preset during system initialization, identifies the next level into which a replacement data word is written on a first in-first out basis. The round robin count for each address location of cache indentifying the next level to be written is stored in a random access memory (RAM). The contents of a particular address location of RAM is incremented each time replacement information is written into that address location in cache.

Abstract: A data processing system includes a central processor subsystem, a main memory subsystem and a cache subsystem, all coupled in common to a system bus. During the overall system initialization process, apparatus in the cache subsystem effects the transfer of information from the main memory subsystem to the cache subsystem to load all address locations of the cache subsystem. The transfer of information from the main memory subsystem to the cache subsystem starts from the lowest order address locations in main memory and continues from successive address locations until the cache subsystem is fully loaded. This assures that the cache subsystem contains valid information during normal data processing.

Abstract: A Data Processing System comprises a central processor unit, a main memory and a cache, all coupled in common to a system bus. The central processor unit is also separately coupled to the cache. Apparatus in cache is responsive to signals received from the central processor unit to initiate a test and verification mode of operation in cache. This mode enables the cache to exercise various logic areas of cache and to indicate to the central processor unit hardware faults.

Abstract: A data processing system includes a plurality of system units all connected in common to a system bus. Included are a main memory system and a high speed buffer or cache store. System units communicate with each other over the system bus. Apparatus in the cache store monitors each communication between system units to determine if it is a communication from a system unit to main memory which will update a word location in main memory. If that word location is also stored in cache then the word location in cache will be updated in addition to the word location in main memory.

Abstract: A data processing system having a system bus; a plurality of system units including a main memory, a cache memory, a central processing unit (CPU) and a communications controller all connected in parallel to the system bus. The controller operates to supervise interconnection between the units via the system bus to transfer data therebetween, and the CPU includes a memory request device for generating data requests in response to the CPU.

Abstract: A data processing system includes a plurality of system units all connected in common to a system bus. The system units include a central processor (CPU), a memory system and a high speed buffer or cache system. The cache system is word oriented and comprises a directory, a data buffer and associated control logic. The CPU requests data words by sending a main memory address of the requested data word to the cache system. If the cache does not have the information, apparatus in the cache requests the information from main memory, and in addition, the apparatus requests additional information from consecutively higher addresses. If main memory is busy, the cache has apparatus to request fewer words.

Abstract: A digital computing system includes an addressable read only memory for storing microprogram control words. A plurality of the microprogram control words each include a predetermined bit used for branching. When the predetermined bit within a control word is not set, the next microprogram control word is read from the next microprogram memory address. When the predetermined bit is set, the next microprogram word is read from the microprogram memory address having a value which corresponds to the next address plus a weighted value of the predetermined bit.

Abstract: An apparatus for increasing the capacity and speed of access of a large microprogram read only memory. The apparatus incorporates the use of a four bit control field in a microinstruction word which is set into a hardware register to extend the address beyond the normal range of the addressing capability of the microinstruction word. The four bits stored in the hardward register allow one of a maximum of sixteen read only memory banks to be selected. The word in the selected bank is selected by the normal range. This technique also allows the selection of another of the read only memory banks in one machine cycle.