DDR SDRAM Standard Frequency (MHz) Voltage
DDR 100–200 2.5/2.6
DDR2 200–533 1.8
DDR3 400–800 1.5
DDR (DDR1) has been superseded by DDR2 SDRAM, which has some modifications to allow higher clock frequency, but operates on the same principle as DDR. Competing with DDR2 are Rambus XDR DRAM. DDR2 has become the standard, as XDR is lacking support. DDR3 SDRAM is a new standard that offers even higher performance and new features.
DDR's prefetch buffer depth is 2 bits, while DDR2 uses 4 bits. Although the effective clock rates of DDR2 are higher than for DDR, the overall performance was no greater in the early implementations, primarily due to the high latencies of the first DDR2 modules. DDR2 started to be effective by the end of 2004, as modules with lower latencies became available.
Memory manufacturers have stated that it is impractical to mass-produce DDR1 memory with effective clock rates in excess of 400 MHz. DDR2 picks up where DDR1 leaves off, and is available at clock rates of 400 MHz and higher. RDRAM is a particularly expensive alternative to DDR SDRAM, and most manufacturers have dropped its support from their chipsets. DDR1 memory's prices have substantially increased since Q2 2008 while DDR2 prices are reaching an all-time low. In January 2009, 1 GB DDR1 is 2–3 times more expensive than 1 GB DDR2. High density DDR RAM will suit about 10% of PC motherboards on the market while low density will suit almost all motherboards on the PC Desktop market.