DDR2 SDRAM is short for Double Data Rate Two Synchronous Dynamic Random Access Memory. It is a RAM (Random Access Memory) technology commonly used in electronic engineering for high-speed storage of data in a personal computer or other digital devices.
It is part of the SDRAM (Synchronous Dynamic RAM) family known for storing memory in memory cells. It is the second generation of DDR SDRAM and one of the many DRAM (Dynamic RAM) implementations. DDR2 SDRAM is an evolutionary improvement over its predecessor.
Improvements in the DDR2 SDRAM
DDR2 SDRAM has the following features:
- DDR2 SDRAM can run the external data bus at a rate that is two times as fast and efficient than the original DDR. It can transfer four bits of data per memory cell cycle. This innovation is possible because the original clock rate of the DDR is abandoned, operating half the clock rate (one quarter of the data transfer rate) of the memory cells.
- There is an improvement in the prefetch buffer of DDR2 SDRAM. It is now four bits deep compared to DDR SDRAM’s two bits deep prefetch buffer width.
- DDR2 SDRAM has read latencies between four and six cycles, twice higher compared to DDR SDRAM. This needs twice as much bus speed to achieve equal latency.
- It operates on 1.8 V compared to DDR SDRAM’s 2.5 V.
Prefetch buffers are memory cache placed on recent RAM modules that store data prior to its actual usage. The thickness of the prefetch buffer increases with every succeeding advancement in the modern DDR SDRAM modules. This helps in keeping up with the decrease in heat production and increase in bandwidth, CAS latency, and operation frequencies.
In addition, due to its lower memory clock frequency, it facilitates power reduction in applications that do not require high-speed action.