Q. Overclocking RAM, what does that mean?

Q. I have heard of overclocking RAM – Is this possible at all?

A. Yes, a computer has a standard memory speed it is designed for, and it is possible to increase the memory speed, if your memory and computer BIOS are capable of doing it.
Before you go too much further, many notebooks, business desktop computers and entry level name brand machines do not let you access the BIOS to make changes, so overclocking is a non-starter with those machines.

Its All About the Timing: All memory is sold with a set of timings that the manufacturer guarantees it will work at. Typical timings might be DDR4-2400 (2400 MT/s – often incorrectly called 2400 MHz) at CAS Latency 17 (CL17). The higher the MT/s the better, the lower the CL number, the better. The two measures are linked, the overall speed is a combination of the transaction rate AND the number of clock cycles it has to wait for latency.

You can improve the performance of your machine by increasing the memory speed (MT/s) and lowering the latency (CL) by adjusting the settings in the motherboard’s BIOS. Whether you can speed the memory up depends on:

  • Your BIOS, and whether the manufacturer allows you to change the settings,
  • Your memory controller, which is built into the CPU of all modern machines,
  • Your motherboard, whether it can deliver stable voltages to the memory, and
  • The memory itself, whether it can keep up with the faster timings.

The numbers interact – its more difficult to maintain low latency in a chip as the speed goes up. In performance testing, a tight latency DDR4-3200 CL14 setup performs approximately the same as a DDR4-3600 CL16 setup. What the 3600 gains in speed it gives away in extra latency. Here’s a simple latency calculator that does the math so you can compare the actual latency time in nanoseconds.

Buying memory: Memory for overclocking is sold (often marketed as Gaming memory), by a number of manufacturers. Each kit will be selected and tested to perform at higher than standard speeds. The price goes up rapidly as the speed ratings go up and the latency goes down, mainly because the manufacturers have to sift through the component chips to find the few that will tolerate higher speeds. When a memory kit is rated at, for example, 4000 MT/s that means that its maximum speed is 4000 MT/s. But you can set it to any speed you like under that maximum. Its important to remember that the RAM modules doesn’t set the speed, the BIOS does. In fact, it you plunked that expensive 4000 kit into a motherboard stock, it would run it at the standard JEDEC speed of 2133 MT/s or perhaps 2400 MT/s. It won’t run faster speeds until you adjust the BIOS yourself.

What does your CPU want? Your CPU has a “native” maximum speed at which it is guaranteed to handle RAM. The supported maximum native speed of the AMD Ryzen 3xxx series is 3200 MT/s and the 9th generation Intel Core CPUs is 2666 MT/s. RAM at these speeds are the safe choice right out of the box.

Beyond those speeds, you can dial in your own BIOS settings for speed and latency, or if the memory and the BIOS both support it, you can enable XMP (eXtreme Memory Profile) and choose one of the ‘standard’ XMP overclocking profiles. Motherboards sold for gaming and do it yourself builds often come with enhanced BIOS screens, or Auto Tuner or Intelligent Overclock Assistant apps to make it easier to experiment.

Every manufacturer’s BIOS looks a little different, but the basics will be there under DRAM Speed or Memory Clock and the details of latency under DRAM Timing.

You can do some research online for the best combination of MT/s and CL rating for your particular processor. The general consensus is that AMD processors benefit more from faster memory performance than Intel.

Also, any computer that uses on-board graphics (the video ‘chip’ embedded in the CPU chip) will benefit disproportionately from faster RAM, because the same System RAM memory is used for Video memory, rather than the GPU on a discrete video card having its own fast GDDR video memory to work with. In a shared video memory setup, slow RAM will compromise video performance as well as general computing performance.

AMD Ryzen2: AMD suggests that the ‘sweet spot’ in performance for Ryzen 3xxx CPU line is 3600 MTs. For technical reasons, memory performance actually slows down when the clock is pushed further than 1800 MHz (recall that DDR memory executes 2 operations on each memory clock tick, so 1800 MHz mclock = 3600 MT/s DDR4 speed). You can make up the performance with some custom timing tweaks, but for most people, the XMP profile at 3600 MT/s is going to be the easiest and most reliable overclock. So for this approach, setting the mclock to 1800 MHz, (DDR4-3600) and then reducing the latency settings, would be the way to go. For a smaller budget, get the lowest latency DDR4-3200 MT/s that you can afford.

Intel: For Intel Core 9th generation CPUs, its not so easy to generalize, because it depends a lot on what software you are using. In tests for gaming performance, there was little improvement going higher 3000 MT/s CL14. In graphic professional software, 3000 MT/s CL14 was good, but a low latency 3200 MT/s setup seems optimal. In the exceptional cases of doing intense 3D rendering, compression and encoding, faster RAM in the 3600 MT/s range can deliver improvements

No Guarantees: Even if memory is rated for a high speed, it doesn’t mean that your particular combination of memory, CPU and motherboard will be stable at the highest speed. Every overclock is a trial and error process, and is partially dependent on the luck of the draw: whether your individual chips will handle aggressive timings or not. Needless to say if you overclock the memory beyond the rated speed of the RAM module, all bets are off; you can expect instability and worse.

Really No Guarantee: Reaching the highest speed of a memory module usually requires boosting the memory power supply voltage above the standard 1.2V (for DDR4). You should investigate the voltage range that the memory modules are guaranteed to tolerate, and if you exceed that voltage, it is at your own risk. RAM damaged from over voltages may not be covered by the manufacturer’s warranty.

Q. So if I can overclock, is it advisable?

A. It depends. If you are seeking the fastest performance for your machine bar the cost, then you would invest in faster RAM. The investment will not only be in the more expensive RAM modules, but in considerable time on your part to adjust and test the machine until you arrive at the fastest stable speed.

If you want stability and long life, (or simply less hassle) you will stay with the manufacturer supported speed ratings.

One thing you will find quite quickly when overclocking RAM, is that if you push the speed too high or the latency timings too tight, the chips on the memory won’t be able to keep up, and the machine will crash, either at boot up, or worse, sporadically as you are using it. So you want to pull back one or two steps from the edge in order to maintain stability.

Also, achieving higher speeds often means increasing the voltage supply to the memory, which generates additional heat, and in general could mean that the memory will fail sooner as it is under greater stress. Worst case scenario is that going to far with voltage increases could damage the CPU as well. These voltage related failures would theoretically void the warranties of the hardware.

More about Latency: In simple terms, Latency is the amount of time that the memory chip needs to return information from a request. This imposes a pause between successive operations. CAS Latency (CL) is the most common measure and is an easy shorthand for the performance of the memory chip. But there are several other measures of latency, which is why you may see RAM modules specified as, for example CL 16-18-18-36 The first figure is the CAS Latency (CL16). Here is an article which discusses latency in more detail.

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