What’s the difference between SDRAM, DDR, DDR2, DDR3, DDR4 and DDR5?

All desktops, laptops and tablets use random-access memory (RAM) to store the short-term data they need to function. As computers evolve, RAM  improves too.

Computers built before 2002 generally used synchronous dynamic random-access memory (SDRAM). Fast forward to 2021, and memory technology took a revolutionary stride with DDR5 DRAM. During the years in between, several generations of RAM entered the market.

Each generation of RAM increases speed and frequency while decreasing power consumption. Since computer hardware is all connected and interdependent, this can lead to speed increases in other components, too, which is why upgrading your memory is a great way to fix a slow computer.

Since the differences between the generations of RAM can be confusing, we created this explainer to give you clear insights and fair comparisons so you can build your own PC, upgrade your computer, or just understand more about RAM.

What is SDRAM?

SDRAM was developed in 1988 in response to increased speeds of other computer components. The "synchronous" in its name is a clue — SDRAM modules are designed to automatically synchronize with the timing of the central processing unit (CPU).

Just like a clock, the memory controller knows the exact cycle when the requested data will be ready, meaning the CPU doesn't have to wait between memory accesses. SDRAM can only read/write one time per clock cycle.

What is DDR?

DDR, short for double data rate, was introduced in 2000 as the next generation following SDRAM. DDR transfers data to the processor on both the downbeat and upbeat of the clock signal, so twice per cycle. Using both beats to transfer data makes DDR memory significantly faster than SDR memory, which uses only one edge of the clock signal to transfer data.

The process of the DDR transferring two bits of data from the memory array to the internal input/output buffer is called 2-bit prefetch. DDR transfer rates are usually between 266 and 400MT/s. Bear in mind that double data rate is different from dual-channel memory.

Over time, DDR technology has evolved to handle improvements to other components and has enhanced overall computer performance. We'll now explore and compare each generation of DDRAM.

Prefetch 1 - Bit 2 - Bit
Data Rate (MT/s) 100 - 166 266 - 400
Transfer Rate (GB/s) 0.8 - 1.3 2.1 - 3.2
Voltage (V) 3.3 2.5 - 2.6

DDR vs. DDR2

DDR2 was introduced in 2003 and operates twice as fast as DDR due to an improved bus signal. DDR2 uses the same internal clock speed as DDR, however, the transfer rates are faster due to the enhanced input/output bus signal. DDR2 has a 4-bit prefetch, which is twice that of DDR. DDR2 can also reach data rates of 533 to 800MT/s.

DDR2 memory can be installed in pairs to run in "dual channel mode," which can increase memory throughput even more.

   DDR  DDR2
Prefetch  2 - Bit  4 - Bit
Data Rate (MT/s)  266 - 400  533 - 800
Transfer Rate (GB/s)  2.1 - 3.2  4.2 - 6.4
Voltage (V)  2.5 - 2.6  1.8

DDR2 vs. DDR3


In 2007 DDR3 technology was introduced with not only 2x the bandwidth and transfer rates of DDR2, but  a significant reduction in power consumption – roughly 40% compared to DDR2.  . This reduction from 1.8 to 1.5V  meant lower operating currents and voltages, which was fantastic news for battery operated devices.. DDR3 transfer rates are between 800 and 1600MT/s.

All these improvements meant higher bandwidth and performance  with less power consumption, making DDR3 a great memory option for laptops.

   DDR2 DDR3
Prefetch 4 - Bit 8 - Bit
Data Rate (MT/s) 533 - 800 1066 - 1600
Transfer Rate (GB/s) 4.2 - 6.4 8.5 - 14.9
 Voltage (V) 1.8  1.35 - 1.5    

DDR3 vs DDR4


Seven years after the release of DDR3, DDR4 became available. The DDR4 has lower operating voltage with 1.2 V, and has higher transfer rates than previous generations, processing four data rates per cycle. This means DDR4 consumes less power and is faster and more efficient than DDR3. This newer generation also introduced bank groups to avoid having a prefetch of 16, which isn’t desirable. With bank groups, each group can execute 8-bits of data independently from the other, so DDR4 can process multiple data requests within a clock cycle.

DDR4 transfer rates are continually rising, as DDR4 modules can reach speeds of 5100MT/s and even higher when overclocked. Crucial Ballistix MAX modules broke numerous overclocking world records in 2020.

   DDR3 DDR4
Prefetch 8 - Bit Bit per Bank
Data Rate (MT/s) 1066 - 1600 2133 - 5100
Transfer Rate (GB/s) 8.5 - 14.9 17 - 25.6
 Voltage (V) 1.35 - 1.5  1.2  

DDR4 vs DDR5


DDR5 was introduced in 2021, and is the most recent generation of memory technology, marking a revolutionary jump in architecture. It’s arguably the biggest jump in memory technology we’ve seen since SDRAM.

DDR5 brings better channel efficiency, improved power management, and optimized performance - enabling next-generation multi-core computing systems. DDR5 launch speeds deliver nearly double the bandwidth of DDR4. It also allows scaling memory performance without degrading channel efficiency at higher rates. These results aren’t just during testing but under real-world conditions.

DDR5 memory standard is a denser memory stick and equates to more memory capacity in your system. In comparison, the DDR4 stopped at 16-gigabit memory chips, but DDR5 offers up to 64-gigabit memory chips. Crucial DDR5 memory will operate at 4800MT/s at launch, 1.5x the maximum standard DDR4 speed.

   DDR4  DDR5
Prefetch  Bit per Bank  16 - Bit
Data Rate (MT/s)  2133 - 5100  3200 - 6400
Transfer Rate (GB/s)  17 - 25.6  38.4 - 51.2
 Voltage (V)  1.2  1.1 

Comparing RAMs in numbers

Prefetch 1 – Bit 2 - Bit 4 - Bit 8 - Bit Bit per Bank 16 - Bit
Data Rate (MT/s) 100 - 166 266 - 400 533 - 800 1066 - 1600 2133 - 5100 3200 - 6400
Transfer Rate (GB/s) 0.8 - 1.3 2.1 - 3.2 4.2 - 6.4 8.5 - 14.9 17 - 25.6 38.4 - 51.2
Voltage (V) 3.3 2.5 - 2.6 1.8 1.35 - 1.5 1.2  1.1

Memory is not compatible across all motherboards

Generally speaking, motherboards are built to support only one type of memory. So, you can't mix and match SDRAM, DDR, DDR2, DDR3, DDR4, or DDR5 memory on the same motherboard, as they won't function. They may not even fit in the same sockets.

RAM systems are industry-wide standardized, so you need to know the electrical parameters and physical shape of the memory hardware installed in your computer. Because the electrical parameters are different for each generation of memory, the physical form of the memory changes to prevent the wrong memory from being installed in a computer. For example, choosing between SDRAM vs DDR5 isn't possible as motherboards can only use a particular memory specification. Some forms of memory are cross-compatible, but your system will only work with the appropriate RAM.

To figure out the right kind of memory for your computer, use the Crucial® Advisor™ tool or the System Scanner tool. These will tell you which memory modules are compatible with your computer, along with options for your speed requirements and budget.


FAQs on RAM Generations

  • What does DDR stand for?

    DDR stands for Double Data Rate. DDR transfers data to the processor on both the rising and falling edges of the clock signal, so twice per cycle.

  • What does RAM do?

    RAM is your computer's short-term memory. Whether you're using a desktop, laptop or tablet, they'll all have RAM to store short-term data that your device requires to operate correctly. The latest RAM technology is DDR5.

  • Is all RAM compatible with all motherboards?

    No, not all RAM is compatible across all motherboards. Motherboards are built to support only one type of memory, so you can't mix and match SDRAM, DDR, DDR2, DDR3, DDR4, or DDR5 memory on the same motherboard. They won't work, and they may not even fit in the same sockets.

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