A co-processor (also called "memory co-processor") provides an interface to a memory, by executing instructions on data held in the memory. The co-processor uses a specified address to fetch data from memory, performs a specified instruction (such as incrementing a counter or policing) on the data to obtain modified data, and writes the modified data back to memory at the same address. Depending on the embodiment, the memory co-processor may include a first buffer for holding instructions that may be received back to back, in successive clock cycles. Instead of or in addition to the first buffer, the memory co-processor may include a second buffer for holding data to be written to memory back to back, in successive clock cycles. In some embodiments, the memory co-processor also receives (and maintains in local storage) the identity of a task that generates the specified instruction, so that the same cask may be awakened after the instruction has been executed.