This paper presents a configuration memory architecture that offers fast FPGA reconfiguration. The underlying principle behind the design is the use of fine-grained partial reconfiguration that allows significant configuration re-use while switching from one circuit to another. The proposed configuration memory works by reading on-chip configuration data into a buffer, modifying them based on the externally supplied data and writing them back to their original registers. A prototype implementation of the proposed design in a 90nm cell library indicates that the new memory adds less than 1% area to a commercially available FPGA implemented using the same library. The proposed design reduces the reconfiguration time for a wide set of benchmark circuits by 63%. However, power consumption during reconfiguration increases by a factor of 2.5 because the read-modify-write strategy results in more switching in the memory array.