DDR (double data rate) SDRAM is the latest evolution in random access memory (RAM) technology. All SDRAM operates on a system frequency or "bus" speed measured in mega hertz (MHz). Traditional SDRAM used only the rising edge of the clock cycle to transfer data. The new DDR SDRAM transfers data on both the rising and falling edge of the clock. PC2100 is the common name for the JEDEC specification for DDR which runs on a 133MHz bus speed (266MHz double data rate). The chips themselves are named in a more conventional way as "DDR-233" where the name reflects their MHz speed, the modules however are named for the effective data transfer of 2100 MB/sec (2.1 GB/sec) on a 64-bit bus.

PC2100 DDR uses either DDR-266a or DDR-266b chips. The DDR-266a chips are the fastest bin rated for CAS2 operation at 266MHz, we use those on our High Performance DDR SDRAM. DDR-266B chips are rated for CAS2.5 at 266MHz operation. The chips on our Special DDR and our Hyundai DDR are rated DDR-266b. Both of these types of modules are programmed for CAS 2.5-3-3 operation at 266MHz via the serial presence detect (SPD) EEPROM. PC2100 DDR is designed for use with CPUs which run on a 133MHz FSB (266MHz DDR). Although the increase in bus speed from 200MHz to 266MHz does translate to an increase in performance, a much larger gain comes from using DDR which runs at lower latencies. If the fastest possible performance from your system is important to you, we recommend using our High Performance DDR with the lower latencies.

Please consult our DDR mainboard qualification page to see a list of chipsets which have been approved as compatible with our DDR modules.