Arrangement of data within cache lines so that tags are first data received

Abstract

A memory system includes a main memory controller supplying data in response to transactions received by the main memory controller. A plurality of modules each include a cache memory for storing data supplied by the main memory controller. The modules request data from the main memory controller by sending module generated transactions to the main memory controller. A cache tag array includes a cache tag corresponding to each data line stored in memory, there being a one-to-one correspondence between the cache tags and the data lines. The data lines together with their associated cache tags are combined and arranged in a plurality of sequential data chunks, the cache tags included in an initial portion of the data chunks (i.e, a first sequence of bits) followed by inclusion of the data lines in a subsequent portion of the data chunks (i.e., the usable bit positions following inclusion of all of the cache tag bits.) Each of the chunks may further include appropriate ECC bits. By this arrangement, all of the cache tags are transferred between the main memory controller and the plurality of modules prior to transfer of the bits constituting the data lines so that any coherency operations may be initiated without waiting to receive the remaining data of the data line.