In order to overcome some of the inherent latency problems with standard DRAM memory modules, several manufacturers have included a small amount of SRAM directly into the chip, effectively creating an on-chip cache. One such design that is gaining some attention is ESDRAM from Ramtron International Corporation.
ESDRAM is essentially SDRAM, plus a small amount of SRAM cache which allows for lower latency times and burst operations up to 200 MHz. Just as with external cache memory, the goal of a cache DRAM is to hold the most frequently used data in the SRAM cache to minimize accesses to the slower DRAM. One advantage to the on-chip SRAM is that a wider bus can be used between the SRAM and DRAM, effectively increasing the bandwidth and increasing the speed of the DRAM even when there is a cache miss.
As with DDR SDRAM, there is currently at least one Socket 7 chipset with support for ESDRAM. The deciding factor in determining which of these solutions will succeed will likely be the initial cost of the modules. Current estimates show the cost of ESDRAM at about 4 times that of existing DRAM solutions, which will likely not go over well with most users.