History

• DDR2 technology was introduced in 2003 but actually did not perform better than its predecessor DDR. It was not until 2004 that DDR2 technology outperformed DDR technology and started to become the standard SDRAM DDR modules used in computers.
  
  

Type

• DDR2 is a type of SDRAM technology. According to PCMAG.com, SDRAM (synchronous dynamic random access memory) is technology in RAM modules that allow them to have a block of memory being accessed while the other block is prepared for access. DDR (double data rate) doubles the data transfer rate. DDR2 technology further increases the DDR data transfer rates.
  
  

Speeds

• According to PCMAG.com, the memory speed of DDR2 RAM modules ranges from 200 MHz to 533 MHz. The channel data rate ranges from 3.2 GB/sec to 8.5 GB/sec.
  
  

Physical

• DDR2 RAM modules have 240 pins whereas DDR RAM modules have 184 pins. DDR2 modules are not compatible with DDR memory sockets.