[TECH] What is the difference between DDR3, DDR2, DDR, and SDRAM?

Most desktops and notebooks use one of four popular types of dynamic random access memory (DRAM) for the main system memory.

Single data rate (SDR) SDRAM is the older type of memory, commonly used in computers prior to 2002. 

Double data rate (DDR) SDRAM hit the mainstream computer market around 2002 and is a straightforward evolution from SDR SDRAM. The most significant difference between DDR and SDR is that DDR reads data on both the rising and falling edges of the clock signal, enabling a DDR memory module to transfer data twice as fast as an SDR memory module. 

Systems implementing the follow-on technology to DDR, called DDR2 began to appear in mid-2004. DDR2 achieves speeds beyond that of DDR, delivering bandwidth of up to 8.5 GB per second. Frequently, DDR2 based systems can use memory installed in pairs to run in "dual channel mode" to increase memory throughput even further. 

The latest generation of memory technology, DDR3, began to appear in systems in late 2007. DDR3 is an evolutionary step beyond DDR2 and operates at lower voltages, thereby consuming less power, and can transfer data at rates up to 12.8 GB per second. Typically, DDR3 based systems can address memory modules in banks of 1, 2 or 3. If a system supports it, installing memory in matched sets of 2 or 3 modules (dual channel or triple channel modes) will deliver greatly increased memory performance over running a single memory module by itself. 

Generally speaking, motherboards are built to support only one type of memory. You cannot mix and match SDRAM, DDR, DDR2, or DDR3 memory on the same motherboard in any system. They will not function and will not even fit in the same sockets. 

The right type of memory to use is the one that your computer takes! The easiest way to find the right memory for your computer is to look up your system in Crucial's Memory Advisor tool. The Memory Advisor tool will list only compatible memory for your system. 

If you don't know the exact model of your computer, the Crucial System Scanner can scan your computer hardware to automatically detect your system configuration and give you a report on which upgrade is right for you. 

Others Explaination:

Difference between DDR2 and DDR3 RAM

What are DDR2 and DDR3 RAM? Are they really different? The Answer is yes. DDR2 and DDR3 are two different types of RAM (Random Access Memory). DDR2 RAM is also known as DDR2SDRAM (Double Data Rate Synchronous Dynamic Random Access Memory2) and DDR3 RAM is aka DDR3SDRAM (Double Data Rate Synchronous Dynamic Random Access Memory3). How are they different? DDR2 and DDR3 RAMs differ mainly in the way they operate and in their operation speeds. DDR2 stands for double data rate 2 while DDR3 is the third generation of DDR RAMs which has got many advantages than its predecessor DDR2. In a simple way, the difference may be felt just in the numbers, where that number is the difference between two different generations of computers and what are they able to handle.

DDR2 RAM Specifications

DDR2 RAM is the second generation among all others in the DDR RAM family. DDR2 has a lowest speed level of 400MHz available as of now  which was the highest speed level for its predecessor DDR1 RAM. DDR2 starts up where DDR1 left off. Because of different latencies a 400MHz DDR1 will outperform a 400MHz DDR2. But there is definitely an advantage that returns to DDR2 when the speed reaches 532MHz which is the next step, DDR1 cannot reach this state. DDR2 achieves performance gain using a pre fetch buffer which is used to retrieve four data words per memory access. The pre fetch buffer allows a data transfer of four times per clock cycle.

DDR3 RAM Specifications

DDR3 RAM is the third generation in the DDR group of RAMs. DDR3 starts up at a lowest speed level of 800MHz and the maximum is 1600MHz, provided the bus speed is as high as 2000MHz. The major benefit of DDR3 is higher performance with lower power consumption. The operating volume for DDR3 is 1.5V where as it is 1.8V for DDR2. In DDR3 lowest heat level is reached, so that the system will run cooler compared to DDR2. DDR3 allows data transfer twice per clock cycle similar to other forms of DDR. However, the pre fetch buffer in DDR3 can transfer data eight times per clock cycle. This enables a maximum data transfer twice that of DDR2.

DDR2 and DDR3 RAMs differ mainly in performance, Compatibility, clock speed etc.

Advantages of DDR3 over DDR2

Higher bandwidth performance, maximum up to 1600 MHz: This can be achieved using the 8 bit pre fetch buffer.

Higher performance at low power (longer battery life in laptops):DDR3 memory offers a high performance rate by consuming very less power in a very effective manner.

DDR3 provides enhanced low power features to the users.

It has an improved thermal design, the cooler.

Disadvantages ofDDR3 compared to DDR2

DDR3 is highly expensive: as of now the DDR3 costs much more than that of DDR2.

DDR3 usually has higher CAS latency: this is achieved because the clock cycles used to measure the latency are shorter. The typical available CAS latencies for a JEDEC DDR2 device are 5-5-5-15, whereas the normal available latencies for the new JEDEC DDR3 devices are 7-7-7-20 for DDR3-1066 and 7-7-7-24 for DDR3-1333.

Summary

• DDR3 is costlier than DDR2
• DDR3 is not backward compatible with DDR2.
• DDR3 modules have got comparatively less power latencies than DDR2.
• DDR3 has come up with a higher bandwidth rate than that of DDR2.
• DDR3 has a less power consumption than the DDR2 RAM
• The DDR3 memory clock runs at quarter speed of the system clock whereas the DDR2 memory clock runs at half the speed of the system clock.

Purchasing a RAM which is DDR2 or DDR3 doesn’t matter what is your preference in that case. The main thing is they are not compatible with each other. So if your motherboard has DDR2 RAM you cannot upgrade it to DDR3 RAM without a motherboard upgrade. 

- See more at: http://readanddigest.com/difference-between-ddr2-and-ddr3-ram/