Difference Between DDR2 and DDR1

Folks! Recall Moore’s law…I don’t really wanna repeat it myself this time, though. Well, actually the attention I want to draw on is to make you confess that the computer technologies have improved greatly over the past few years and this has something to do with the Moore’s law.. The memory of computers has also evolved a lot from RAM, DRAM and SDRAM. Then came DDR-SDRAM and now DDR2-SDRAM. We should not concern ourselves with the very old models of RAM since those are no longer in use in most parts of the world.

SDRAM (Synchronous Dynamic Random Access Memory) is a type of memory that requires power to hold its data. This is the prevalent memory used in computers right before the introduction of DDR-SDRAM (Double Data Rate SDRAM). DDR improves upon the architecture of SDRAM by a process known as “double pumping”. Instead of transferring data once every clock cycle, DDR changes its data state twice every cycle. Once on the rising edge, then another on the falling edge. This is true for both DDR and DDR-2. So why is DDR-2 better than DDR?

Actually, when DDR-2 came out, it was actually worse than DDR. The original DDR memory has its memory clock synchronized with the bus clock, allowing 2 bits to be transferred every clock cycle. DDDR-2 changes this by doubling the bus speed while still holding the memory clock at the same frequency. So that at every memory cycle, 4 bits of data is transferred. The trade-off to this is the higher latency of DDR-2 memory compared to DDR memory when operating at the same bus frequency.

In order to obtain the same performance as a DDR running at 100 MHz bus speed, DDR-2 memory must be run at 200 MHz. But if we look at the clock speed, the DDR is also working at 200 MHz while the DDR-2 is only at 100 MHz. If we have a DDR-2 chip that operates at the same clock speed as DDR-1, then we can see that it has double the throughput.

Memory clock speed is very important because producing chips with higher clock speeds is very expensive since in every batch of chips produced, only a small amount of it are capable of higher clock speeds. So, if we compare two chips that are similarly clocked, the DDR-2 would be cheaper. And, if we compare two chips that are similarly priced, the DDR-2 would be faster. The technology of DDR also ends where DDR-2 begins, meaning that DDR chips can no longer be improved further due to restrictions in cost while DDR-2 goes far beyond the capabilities of DDR. The capabilities of DDR-2 also have its limits, mainly as the clock speed gets higher, that’s where DDR-3 comes in. But that’s another story altogether.