RAM, which stands for Random Access Memory, is a short-term storage location your computer uses for running processes. You might not think much about RAM besides the amount of it when buying a new computer.
But not all RAM is created equal. Different generations of RAM provide different speeds and are only compatible with certain systems. Here are the differences between DDR2 and DDR3 RAM, compared to the newer DDR4 RAM.
What Is DDR RAM?
If you’re new to RAM, you might not know what “DDR” means. This abbreviation stands for double data rate.
In simple terms, operating at a double data rate means the RAM can transfer data two times per clock cycle. As you probably know, all data on a computer is digital, meaning it’s represented by a 1 (on) or a 0 (off).
One clock cycle is represented by the CPU signal going from off to on and back again. This is usually measured from the halfway point, as you can see in the chart below.
This double data rate is a major upgrade from old SDR (single data rate) RAM, which only operated once per clock cycle. Original DDR RAM first became generally available in 2000, and like SDR RAM, is now obsolete. Virtually all RAM you’ll find available now is some generation of DDR.
But why do these generations of RAM change?
DDR Generations Explained
Original DDR RAM was superseded by DDR2, DDR3, and now DDR4. These are all future generations of the same technology with faster speed and other improvements, and are all the same physical size.
This isn’t out of the ordinary, since many computing standards evolve over time. But you might wonder where DDR2 and DDR3 came from, and why they emerged.
The generation of RAM used with a computer is closely tied to the development of processors and motherboards. As companies like Intel come out with new CPU technology, they require new motherboard chipsets. This is a set of electronic components that let all the parts of a computer communicate properly.
New generations of RAM are necessary to work with the latest chipsets. This is why we’ve seen DDR2, DDR3, and DDR4 RAM after the original generation. Without these advancements, we wouldn’t be able to put RAM into newer systems.
Importantly, RAM is not backwards or forwards-compatible. If your motherboard is designed for DDR4 RAM, DDR3 RAM simply won’t work in it. It’s thus vital when building or upgrading a PC that you buy the right generation of RAM for compatibility.
Each generation of RAM has its notch in a slightly different position, so it’s impossible to put the wrong type in your computer.
DDR2 vs. DDR3 RAM
You might wonder how the newer generations of DDR RAM stack up. Let’s look at DDR2 and DDR3 RAM differences first. While you’re unlikely to find DDR2 RAM in many places today (it did become available back in 2004) it’s still useful for comparison.
While original-generation DDR RAM ran two data transfers per clock cycle, DDR2 RAM can produce four transfers per cycle instead. DDR3 takes this even further, as it can produce eight transfers for every clock cycle.
When it comes to speed, DDR3 is unsurprisingly faster. One way to measure RAM speed is megatransfers per second, or MT/s. This refers to the number of operations the RAM can complete every second; 1MT/s is one million transfers per second.
While DDR2 RAM has data transfer rates ranging from 400 to 1,066MT/s, DDR3 smashes this at 800-2,133MT/s.
Voltage is another important aspect of RAM generations. DDR2 RAM uses 1.8V, while DDR3 is lower at 1.5V. Lower voltage means the RAM uses less power, thus putting less strain on the CPU.
You can find sticks of DDR2 RAM that are 4GB, but the most common maximum is 2GB. Practically, DDR3 RAM caps out at 8GB per stick, though some 16GB sticks are available.
DDR3 vs. DDR4 RAM
Continuing with our discussion of RAM differences, how does DDR4 RAM stack up? DDR3 was introduced in 2007 and while it’s still used with some older systems today, DDR4 has become the standard.
DDR4 runs at an even lower voltage than DDR3, at just 1.2V. It’s also capable of more operations per second, ranging from 1,600MT/s to 3,200MT/s.
Samsung sells a single 32GB stick of DDR4 RAM, but it’s quite expensive. The maximum you’ll see in the wild is usually 16GB.