DDR2 Memory
DDR2 SDRAM is very similar to DDR SDRAM, but doubles the minimum read or write unit again, to 4 consecutive words.
Typical DDR2 SDRAM clock speeds are 200, 266, 333 or 400 MHz (5, 3.75, 3 and 2.5 ns/cycle), generally described as DDR2-400, DDR2-533, DDR2-667 and DDR2-800 (2.5, 1.875, 1.5 and 1.25 ns per beat). Corresponding 240-pin DIMMS are known as PC2-3200 through PC2-6400. Speeds up to DDR2-1250 (PC2-10000) are available for a price.
Note that because internal operations are at 1/2 the clock rate, DDR2-400 memory (internal clock speed 100 MHz) has somewhat higher latency than DDR-400 (internal clock speed 200 MHz).
DDR2 SDRAM or double-data-rate two synchronous dynamic random access memory is a random access memory technology used in electronic engineering for high speed storage of the working data of a computer or other digital electronic device.
It is a part of the SDRAM (synchronous dynamic random access memory) family of technologies, which is one of many DRAM (dynamic random access memory) implementations, and is an evolutionary improvement over its predecessor, DDR SDRAM.
Its primary benefit is the ability to operate the external data bus twice as fast as DDR SDRAM. This is achieved by improved bus signaling, and by operating the memory cells at half the clock rate (one quarter of the data transfer rate), rather than at the clock rate as in the original DDR. DDR2 memory at the same clock speed as DDR will provide the same bandwidth but markedly higher latency, providing worse performance.
Number of Pins
Compare DDR1 and DDR2 Memory
DDR2 is a 240-pin module, DDR is a 184-pin module. Notebooks have 200-pin modules for DDR and DDR2.
debut
DDR2 was introduced in the second quarter of 2003 at two initial speeds: 200 MHz (referred to as PC2-3200) and 266 MHz (PC2-4200). Both performed worse than the original DDR specification due to higher latency, which made total access times longer. However, the original DDR technology tops out at speeds around 266 MHz (533 MHz effective). Faster DDR chips exist, but JEDEC has stated that they will not be standardized. These modules are mostly manufacturer optimizations of highest-yielding chips, drawing significantly more power than slower-clocked modules, and usually do not offer much, if any, greater real-world performance.
Speed
DDR2 SDRAM SDRAM DIMMs - DIMMs based on Double Data Rate 2 (DDR2) DRAM also have data and data strobe frequencies at double the rate of the clock. This is achieved by clocking on both the rising and falling edge of the data strobes. The power consumption and voltage of DDR2 is significantly lower than DDR(1) at the same speed.
* PC2-3200 = 400 MHz data & strobe / 200 MHz clock for address and control
* PC2-4200 = 533 MHz data & strobe / 266 MHz clock for address and control
* PC2-5300 = 667 MHz data & strobe / 333 MHz clock for address and control
* PC2-6400 = 800 MHz data & strobe / 400 MHz clock for address and control
* PC2-8000 = 1000 MHz data & strobe / 500 MHz clock for address and control
* PC2-8500 = 1066 MHz data & strobe / 533 MHz clock for address and control
DDR2-400 100 MHz 10 ns 200 MHz 400 Million PC2-3200 3200 MB/s
DDR2-533 133 MHz 7.5 ns 266 MHz 533 Million PC2-4200
PC2-43001 4266 MB/s
DDR2-667 166 MHz 6 ns 333 MHz 667 Million PC2-5300
PC2-54001 5333 MB/s
DDR2-800 200 MHz 5 ns 400 MHz 800 Million PC2-6400 6400 MB/s
DDR2-1066 266 MHz 3.75 ns 533 MHz 1066 Million PC2-8500
PC2-86001 8533 MB/s
Compatibility
Although not much of a "backward compatibility," faster DDR2 DIMMs can be used with slower DDR2 DIMMs but in such situation, the faster one would run at the speed of the slower DDR2.
DDR2 DIMMs are not designed to be backward compatible with DDR DIMMs. The notch on DDR2 DIMMs is in a different position than DDR DIMMs, and the pin density is slightly higher than DDR DIMMs in desktops. DDR2 is a 240-pin module, DDR is a 184-pin module. Notebooks have 200-pin modules for DDR and DDR2.
Installation
Available Memory Sizes
