What is DDR3 SDRAM?

When we say DDR3 (double data rate) RAM, we usually mean the SDRAM (synchronous dynamic RAM).  In our previous post about the DDR2 SDRAM, we discussed the specifications, standards, limitations, and strengths that the DDR3 predecessor had. It was released in the year 2007 where the modules came equipped with clock speeds between  400MHz and 2066MHz. unlike the DDR2 whose smallest RAM module was 512 MBs, the least module for DDR3 RAM is 1Gb. The highest module capacity is up to 24 Gb.

Double data rate means that the data is transferred during the rising and falling edge of the clock signal. It is faster than the single data rate.  This type of RAM is referred to as synchronous since it is in sync with your computer’s processors.  The dynamic term is used since the RAM has to be constantly refreshed.  The electrons leak and data may be lost hence the need to refresh it from time to time.

Just like the DDR2, DDR3 RAMs have 240 pins for desktop types. However, laptops have modules with only 204 pins. You can use DDR3 RAM sticks on DDR2 motherboards, they are not backward compatible. DRR3 has a lower voltage requirement than DDR2, so placing the DDR3 in the DDR2 memory slot could damage it.  Since people hardly have any knowledge about the difference, manufacturers have placed notches for DDR3 differently from that of DDR2 and DDR1 ram sticks.

History of DDR3

Samsung company introduced the DDR3 prototype. This memory module was underdeveloped since 2002 only to make it public in 2005. However, it was not commercially available until 2007. However, DDR2 chips remained the most demanded chips until the year 2009.

The tides were turned in 2009 because of the release of the Core i7 processors and phenom II from Intel and AMD respectively. The two processors featured internal memory controllers. While the core i7 requires DDR3 to work with, phenom II only recommended it. It was until the year 2011 that the DDR3 accounted for more than 70% of units of RAM sold.


The DDR3 had its prefetch length increased to 8-burst-deep; DDR2 had 4-Burst-deep. This is what made them faster than their predecessor. DDR3 is twice as fast as DRR2 and 4 times faster than DDR1.

Standards and modules

Manufacturers have two ways of making the different variations and generation identifiable.  You will find the RAM label either of these two ways; DDR3-xxx or PC3-xxxx. The former is used to inform you of the RAM transfer rates.  On the other hand, PC3-xxxx is used to denote the RAM`s theoretical bandwidth.

Bandwidth is a function of transfer rate.  To get the bandwidth, multiply by 8 since DDR3 uses the 64-bit data transfer at a time.

If you want to get how many bytes your rams transfers per cycle, multiply the clock rate ( frequency) by 4 and then by 8, and finally by 2. The final product divide by eight.  For instance, say you have 200MHz ram, the transferred data are as follows;

Transferred data = 200 MHz * 4 * 2*64/8

= 12800 MB/s

You did multiply by 4 earlier on because of the bus clock speed.  The 2 in was used in the equation above since it’s double rate data and finally by 64/8 since 8 is the number of bits in one byte.

ECC memory

There is a category of DDR3 RAMS considered error correcting code (ECC) memory. The error correcting code (ECC) stands for error-correcting code. These DRR3 RAMS have extra lane additional byte.  This is meant to detect major errors while correcting minor errors. DDR3 error correcting code (ECC) RAMs have high reliability than normal DDR3 RAM. You will easily notice an ECC RAM since manufacturers usually label them as follows PC3-xxx ECC or PC3-xxx E.

There is a second category referred to as registered or buffered RAM. They are electrically buffered with a register signal. They are manufactured and used where signal integrity is a serious concern. However, buffering RAM stick makes have increased latency. You will know RAM is buffered or registered when you notice an R in the naming. For example, PC38500R. however, if your RAM is unbuffered or not registered, manufacturers may and U in the name, for instance, PC38500U.

There are modules referred to as fully buffered DDR3. To know a fully buffered RAM, check for an F or FB in the designation. You will never use this one on your motherboard since its notch is keyed differently so it cannot physically fit there. It is not possible to use fully buffered modules in the registered module even if they were not keyed differently.

Load-reduced modules

The final DDR3 version is load-reduced modules. They are similar to the buffered modules in so many ways. You will know them if you see LR in the designation. It can retain the parallel attribute of signals while buffering both the control and data lines.

Before we go, let us take a look at low voltage DDR3 RAMs.  They are designated names DDR3L or PC3L.  they are an addendum to the JESD79-3. It was designed for use in low voltage devices.  This RAM standard is designed to use 1.35 voltage sources.  Here are examples of DDR3L RAMs; DR3L‐800 (PC3L-6400), DDR3L‐1066 (PC3L-8500), DDR3L‐1333 (PC3L-10600), and DDR3L‐1600 (PC3L-12800). They are not compatible with 1.5v DDR3 memories

There is another standard were referred to as DDR3 Ultra-low-voltage. It was designed to use 1.5 voltage slots.  It is designated PC3U.

DDR3 SDRAM today

As of 2021, DDR3 SDRAM is still in use today. You might be using one yourself if you purchase a PC as recently as two years ago.  However, if your device is new, it is probably using DDR4.

If you build PC, I would recommend you go the DDR4 instead of DDR3 since they offer better performance, lower consumption, and other impressive attributes such as reduced latency. However, if your budget does allow, you can still go for DDR3. One of my devices is using DDR3 and I have nothing to complain about. The motherboard that you have dictates what other components that will need to go for including cases.

What is important about RAMs is that they come in a standardized form.  This means that even if you are using a mini PC, the RAM stick is the same as that used on large desktops. There are small form factor PC that may not contain the same number of RAM slots as the full-size motherboard. You can read here what is the form factor.



Power consumption

DDR3 RAMs consume less power than their predecessor, DDR2. Dynamic RAM leaks electrons and to solve this, the manufacturers went for dual gate transistors.  While the DDR2 would have their voltage raise to 1.9 v, DDR3 could only allow as high as 1.575 volts because of the stability issues. However, you can raise the voltage to 1.8 v before your RAM gets permanently damaged. You should not go this high. RAMs are mainly made of transistors.


DDR3 RAM speed

Using rising and falling edges of a 400–1066 MHz I/O clock, DDR3 modules can transfer data at a rate of 800–2133 MT/s. The data transfer rate is twice that of DDR2 (400–1066 MT/s with an I/O clock of 200–533 MHz), and four times that of DDR (200–400 MT/s with an I/O clock of 100–200 MHz).

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