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DDR / DDR2
DDR has a data rate of 200/266/333/400 MiB/s compared to DDR2 which has a data rate of 400/533/667 MiB/s, it is clear to see that from a speed point of view DDR2 continues where DDR leaves off. The table below courtesy of the Corsair website helps illustrate other notable differences.
|Data Bus||64 bits||64 bits|
|Data Rate||200/266/333/400 MiB/s||400/533/667 MiB/s|
|Bus Frequency||100/133/166/200 MHz||200/233/333 MHz|
|DRAM Frequency||100/133/166/200 MHz||100/133/166 MHz|
|Densities||256MB 512MB 1GB||256MB 512MB 1GB|
|Prefetch||2 bits||4 bits|
|CAS Latency||1.5,2,2.5||3+, 4, 5|
|Write Latency||1T||Read Latency -1|
Package type refers to the physical layout of modules. DDR memory modules are built using the standard TSOP-II architecture (Thin Small Outline Package) where transistors are laid out in grid formation; DDR2 uses a newer layout named FBGA (Fine Ball Grid Array) which allows a higher transistor count in the same physical package.
A DDR module with TSOP chips
DDR and DDR2 are not compatible with each other. Where DDR has the TSOP package the module interfaces with the slot via 184 pins mounted on the side of the module, DDR2 uses 240 pads mounted on the underside of the module which interface with the slot. The FBGA architecture used in DDR2 allows for much more efficient placement of traces and pads, it being possible to run traces closer to the original source. Both modules are 5.25” in length and to prevent end users inadvertently plugging DDR into a DDR2 slot or vice versa the fitment slot is located differently on the two types.