Double Data Rate DIMM [DDR-DIMM, DDR DIMM, or DDR1] utilizes the JEDEC standard for Double Date Rate [DDR I] SDRAM. This page covers the DDR memory modules, which may also be found as SO-DIMM, and Micro-DIMM module formats. DDR DIMM modules are produced in two different flavors; registered or unbuffered. Registered DIMMs have their address and control lines buffered on the DIMM to reduce signal loading. Because the Registered DIMM requires a buffer they are more expensive then unbuffered DIMMs.
Unbuffered DIMMs do not buffer the address lines and control lines, so they cost less and may be limited in the amount the system may have installed because of system loading. How ever an unbuffered DDR DIMM is able to operate one clock cycle faster then a registered DIMM.
In addition to the DDR1 DIMM module being registered or unbuffered, the physical size of the module may also vary between DIMM, SODIMM, or Mirco-DIMM. The SO-DIMM and Micro-DIMM formats are used in lap-top computers, while the standard DIMM format is used in desk-tops and work-stations.
Refer to the general Memory Module page for a more complete listing of different types of modules, manufactures and descriptions. DDR modules may be purchased in one of the following speed grades:
...DDR SDRAM:....Double Data Rate SDRAM [DDR200, DDR266, DDR333 are standard]
.........PC1600 (DDR-200 SDRAM); Clock Speed: 100MHz, Data Rate: 200MHz, Through-put 1600MB/s
.........PC2100 (DDR-266 SDRAM); Clock Speed: 133MHz, Data Rate: 266MHz, Through-put 2100MB/s
.........PC2400 (DDR-300 SDRAM); Clock Speed: 150MHz, Data Rate: 300MHz, Through-put 2400MB/s
.........PC2700 (DDR-333 SDRAM); Clock Speed: 166MHz, Data Rate: 333MHz, Through-put 2600MB/s
.........PC3000 (DDR-366 SDRAM); Clock Speed: 183MHz, Data Rate: 366MHz, Through-put 2900MB/s
.........PC3200 (DDR-400 SDRAM); Clock Speed: 200MHz, Data Rate: 400MHz, Through-put 3200MB/s
As the name implies, Double Data Rate interfaces provides two data transfers per clock. The clock is differential. The data is registered when the CK goes high [the + side], and /CK goes low [the - side].
The first generation of DDR memory DDR1 is being replaced by DDR2, or DDR3.