Understanding The Various Type Of RAM

SDRAM (Synchronous DRAM)

In the age of Pentium II or Pentium III computer, SDRAM is the most common type of RAM and almost all systems were shipped with it. Today, the SDRAM has become obsolete and taken over by faster and newer generation of RAMs.

DDR SDRAM (Double Data Rate SDRAM)

DDR memory, or double data rate synchronous DRAM (SDRAM), is a memory technology that does exactly as its name implies – double the rate of standard SDRAM.

DDR differs from SDRAM in that it:

• Can operate twice as fast as standard SDRAM.
• Can lead to significant performance improvements over systems with SDRAM.

Even though DDR modules have the same physical dimension as SDRAM modules, they have different number of pins and notches. Therefore, DDR modules will not fit nor work in an SDRAM system. DDR memory can only be used in systems designed specifically for DDR memory technology.

DDR2 RAM

Both DDR and DDR2 RAM are the improved version of the SDRAM. They are able to transmit data on the rising and falling edge of the clock cycle. The conventional SDRAM can only transmit data on the rising edge. For a certain clock frequency, say 100MHz, both DDR and DDR2 RAM can operate at double the clock frequency, i.e. 200MHz. The difference of DDR2 to DDR is a doubled bus frequency for the same physical clock rate. What this means is that for a 100MHz clock frequency, a DDR2 RAM can achieve a speed of 400MHz while DDR RAM only achieves 200MHz.

DDR2 RAM has 240 pins (compared to DDR RAM 184 pins) and it is not backward compatible with DDR RAM. Generally, DDR2 RAM process much faster than DDR RAM

DDR3 SDRAM

The difference between the latest DDR3 and the DDR2 is the faster processing speed and lower power consumption. The DDR3 RAM can process at a maximum speed of 1600Mbps while DDR2 can only achieve 800Mbps. In addition, DDR3 runs at 1.5V as compared to 1.8V of DDR2.

DDR3 RAM is not backward compatibility with DDR2 RAM. While both of them have the same number of pins, the key notch is placed in a different position to avoid the confusion between a DDR3 and DDR2 RAM.