DDR1 vs DDR2
DDR1 and DDR2 belong to the recent DDR SDRAM (double data rate synchronous dynamic random access memory) family of RAMs. Both these RAMs store data in similar type of DRAM arrays. The Initial member of this family was the DDR1 (often called DDR). DDR2 followed DDR1. And, DDR3 is the member that followed DDR2. Each RAM is not compatible with any other RAM in the series. This means, in order to change your RAM from one to the other (for example, upgrading from DDR1 to DDR2 RAM) you need to upgrade your whole motherboard. DDR family of SDRAM has higher transfer rates compared to SDR (single data rate) SDRAM, which was used before the introduction of DDR. Specialty of DDR is the usage of double pumping (transferring on both edges of the clock cycle). In fact the “double data rate” indicates the fact that DDR is twice as fast as SDR running the same clock.
What is DDR1?
DDR1 SDRAM stands for double data rate type one synchronous dynamic random access memory, and it is the first DDR SDRAM in the DDR family. However, DDR1 RAM is not forward compatible with any other members in DDR family due to difference in signaling, voltages, etc. DDR1 can go up to a bandwidth of 1600 MB/s (with a base clock speed of 100Mhz). Pre-fetch buffer depth of DDR1 is 2 bits.
What is DDR2?
DDR2 SDRAM stands for double data rate type two synchronous dynamic random access memory. It is the second member in the DDR family. However, DDR2 RAM is not backward compatible with DDR1. That means you need two types of motherboards for DDR1 and DDR2 RAMs. It uses double pumping to transfer data on both the edges of the clock signal (much like DDR1). DDR2 RAM provides a performance of four data transfers per clock cycle. Therefore DDR2 can provide a maximum transfer rate of 3200 MB/s (with a base clock speed of 100Mhz).
What is the difference between DDR2 and DDR3?
DDR1 and DDR2 are the first and second members belonging to the DDR family of RAMs. DDR2 RAM provides 4 data transfers/cycle, while DDR1 RAM provides only 2 data transfers/cycle. That means if the base clock speed is 100Mhz, then DDR2 RAM will provide 3200 MB/s bandwidth, while DDR1 RAM will provide only 1600 MB/s bandwidth. On the other hand, DDR1 RAM uses 2.5V per chip, whereas DDR2 RAM uses only 1.8V per chip. DDR1 RAM supports 100-200 Mhz I/O bus clock compared to 200-800 Mhz clock in DDR2 RAM. So, in general DDR2 RAM is relatively faster and consumes less power.
However, choosing between a DDR1 RAM and DDR2 RAM is not always a decision based on performance. DDR2 RAM cannot be plugged in to motherboards with DDR1 RAMs. That means, if you already have a DDR1 RAM, you have to upgrade the motherboard to use a DDR2 RAM (most of the times), and that could be costly, too. But in reality, both Intel and AMD have fully committed to DDR3 for the future, meaning that you will have to upgrade your motherboard at some point (if you still have a DDR1/DDR2 RAM), and upgrade to DDR3.