The naming convention recommended by JEDEC - DDR266 = PC2100, DDR333=PC2700

The naming convention recommended by JEDEC is as follows:

Memory chips are referred to by their native speed: 200 MHz DDR SDRAM memory chips are called DDR200 chips, and 266 MHz DDR SDRAM memory chips are called DDR266. DDR DIMM modules are referred to by their peak bandwidth, which is the maximum amount of data that can be delivered per second: A 200 MHz DDR DIMM is called a PC1600 DIMM, and a 266 MHz DDR DIMM is called a PC2100 DIMM.

To illustrate this on a 266 MHz DDR DIMM module: Each module is 64 bits wide, or 8 Bytes wide (each byte = 8 bits). To get the transfer rate, multiply the width of the DIMM module (8 Bytes) by the rated speed of the memory module (in MHz): (8 Bytes) x (266 MHz/second) = 2,128 MB/second or about 2.1 Gigabytes/second. Therefore, the memory module is often referred to as PC2100. Similarly, a PC2700 DIMM module utilizes memory chips rated at 333 MHz.

JEDEC is already finalizing the DDR II spec, which will double the data transfer once more, using the quad-pumped technology that is common in AGP4x bus and the Pentium 4 bus. Speeds of 600-800mhz for DDR are not far away.