A dynamic random access memory with a fast serial access mode for use in a simple cache system includes a plurality of memory cell blocks prepared by division of a memory cell array, a plurality of data latches each provided for each column in the memory cell blocks and a block selector. When a cache miss signal is produced by the cache system, data on the column in the cell block selected by the block decoder are transferred into the data latches provided for the columns in the selected block after selection. When a cache hit signal is produced by the cache system, the data latches are isolated from the memory cell array. Accessing is made to at least one of the data latches based on an externally applied column address on cache hit, and to at least one of the columns in the selected block based on the column address on cache miss.

An instruction translation look-aside buffer (iTLB) for attaining very high data processing throughput comprises a 2.sup.n -way set associative data array having m sets, where m and n are both integers greater than or equal to one, with associated data and tag arrays. A set address selects one of the m sets for reading, resulting in a readout of all 2.sup.n ways of the tag, valid and data arrays. Comparison logic determines if a match exists between the 2.sup.n tags read out from the tag array with a portion of the linear address. A "hit" to a certain way causes a hit line signal to select data for the corresponding way, which is output from a 2.sup.n :1 static multiplexer and contains the physical address translation. Each of the hit lines are precharged during a first phase of a clock cycle. The comparison logic operating during a second phase of a clock cycle. Thus, the matching is accomplished in a single clock cycle.

The present invention is a cache system comprising a data memory for storing data in an external memory, and a tag memory for storing address information for data held in the data memory and a valid data bit indicating whether data controlled by the address information is valid; wherein the address information in the tag memory commonly controls a plurality of data items with consecutive addresses; wherein reading from tag memory is prohibited in a case where an address to be accessed corresponds to data controlled by address information in tag memory that matches a preceding address to be accessed; and wherein tag memory is read and a cache hit determination is performed in a case where the address to be accessed corresponds to data controlled by address information in tag memory that does not match the preceding address to be accessed.

An address translation control circuit which operates in connection with a processor and a translation look-aside buffer ("TLB") to perform virtual-to-physical address translations through shared entries of the TLB. The address translation control circuit comprises a primary context storage element, a group context storage element, a context matching circuit, a comparing unit and a logic unit. The context matching circuit is coupled to primary and group context storage elements to receive their context numbers and reads a context identification number and a context select bit value from a chosen translation entry of the TLB. Concurrently, the comparing unit compares the virtual address contained in that entry with the virtual address requested for translation by the processor. The logic unit receives the outputs from the context matching circuit and the comparing unit and signals operating system software whether an appropriate translation has been found in the TLB.

A write-back cache memory and method for maintaining coherency within a write-back cache memory are disclosed. The write-back cache memory includes a number of cache lines for storing data associated with addresses within an associated memory. Each of the cache lines comprises multiple byte sets. The write-back cache memory also includes coherency indicia for identifying each byte set among the multiple byte sets within a cache line which contains data that differs from data stored in corresponding addresses within the associated memory. The write-back cache memory further includes cache control logic, which, upon replacement of a particular cache line within the write-back cache memory, writes only identified byte sets to the associated memory, such that memory accesses and bus utilization are minimized.