Remember Me: The Expert’s Guide to RAM Overclocking

Posted: April 15, 2013 by: Matt Wilson

WHAT YOU NEED

Components

  • Your RAM Kit. PCPP Recommends: G.Skill Perfect Storm

Programs

  • MaxxMen
    • www.maxxpi.net

  • SuperPi
    • www.superpi.net

  • PiFast
    • bit.ly/mb1Iv6

  • AIDA64
    • www.aida64.com

  • Sandra 2012
    • www.sisoftware.co.uk

Overclocking RAM is something that hasn’t really evolved too much over the years. Sure, it’s changed slightly with the removal of the Front Side Bus on the Intel platform, but the principle has always remained the same. Essentially, all that needs to be done in order to run your RAM at a higher frequency these days is enable XMP (if you’re using a compatible Intel kit and board), or change the bus:RAM ratio accordingly. This should be fairly self-evident from within your BIOS, and as you’re here in The Bunker we’re going to assume a sound understanding on your behalf.

KITTED OUT

Memory manufacturers aren’t all the same. While it is true that some may share the same OEM or fabricator, their binning and selection process may vary greatly. While Corsair was once a great overclocking figurehead, its recent releases haven’t really been able to compete with some of the smaller players in the market.

G.Skill would arguably be the new top overclock-friendly producer, selling 2,400MHz kits en-masse to the wider marketplace, and kits up to 2,800MHz if you’re willing to infiltrate G.Skill and extract some components from the manufacturer’s internal salespeople.

The RAM kit we’d suggest for this memory overclock would be G.Skill Perfect Storm. These kits are usually fairly low latency for their frequency and, given they’re from a large manufacturer, should be fairly easy to find. If your preferred retailer is all out of Perfect Storms, Trident X, also from G.Skill, is still very widely used and should be available at any PC store in the country.

If you prefer other manufacturers to G.Skill, Kingston and Crucial are also making some relatively high frequency kits at around 2,800MHz – though they may be harder to find than the ones previously mentioned. Companies like ADATA and TEAM are also pushing out some fairly competitive kits too, though these still are even harder to track down.

In order to play around in here you should understand how RAM actually works. The important ones are CAS Write latency, Ref Cycle time, Write recovery time and Write to Read Delay. If they are too slow, or set too tight you will get poorer performance or unstable clocks.

TUNE UP

On to the tweaking! RAM frequency is considered widely to be the most important specification of any RAM kit. This is due to the evolution of RAM over the years as we’ve moved from DDR. Now, with DDR3, we’re seeing frequencies and bandwidths our past selves would have killed for. Due to the nature of DDR RAM, we’re seeing transfer speeds up to 64 times faster than on the previous DDR2 technology, which makes overclocking on memory more fruitful now than any other point in the past. With data being transferred 64 bits at a time per memory module, DDR3 SDRAM gives a transfer rate of ×4, for bus clock multiplier; ×2, for data rate; ×64, the number of bits transferred; /8, number of bits/byte. Thus, with a memory clock frequency of 100MHz, DDR3 SDRAM gives a maximum transfer rate of 6400 MB/s.

A general rule of thumb that applies to RAM frequency tweaking: the higher the frequency, the “looser” the cache (CAS) timings need to be in order to remain stable. This is due to the way the I/O bus clock cycle functions.

The most important cache timings are the primary, if you adjust anything it should certainly be these. The command rate of 1 (default can be 2T in a lot of kits) will also help with benchmark scores and bandwidth, though will lower stability.

CACHED UP

When working with the cache timings of your RAM, it is important to work out the clock cycle, or the cycle time in nanoseconds. If you’re running a high frequency with a long cache cycle, your performance will be far from optimized. All this takes is a quick calculation:

(CAS/Frequency (MHz)) x 1000 = X ns

For example, (9/800) x 1000 = 11.25ns. Using this method, it is easy to work out how fast your instruction cycle is running on your existing setup, and you can also work backwards to find the required settings for, say, a cycle time of 3.5ns (lower is always better).

Moving beyond the basics of clock cycles, we find ourselves dealing with sub-timings. Understanding these will allow us to get every last ounce of performance out of our RAM kits. When dealing with cache timings, there are three levels; more specifically, three different command sectors:

  • CL – The clock cycle between sending a column address to memory and the beginning of the data response.
  • tRDC – The clock cycle between row active read and writes.
  • tRP – The clock cycle between row precharge and activate.

Reducing the latency between these three timings will improve the overall responsiveness of your RAM, and, if paired with a high operating frequency, should see you topping out transfer rates well above 18,000MB/s.

One important thing to remember when playing around with cache timings, and indeed with overclocking in general, is that there is no solution or guide that will work for everyone. You will need to spend hours (if not days) fine-tuning your sub-timings in order to find the best performance possible for your RAM kit and your CPU/motherboard Internal Memory Controller.

Click to see graph in full

RE-VOLT

Voltage is a dirty word among amateur overclockers for no other reason than, if abused, it can kill your hardware. While true, it is still very rare that a piece of hardware will die from overvolting alone.

Increasing voltage is a crucial part of finding stability in your overclocks, and if not set properly, voltage alone is one of the largest contributors to an unstable overclock. Many PC gamers simply “up the voltage” until they find stability, though this only works up to a point, as putting too much voltage through any circuit can lead to leaking or shorting as the electrons begin to jump the nanometer gaps over the silicone.

The standard voltage for most RAM kits these days will vary from 1.35v in some low voltage kits all the way up to 1.8v in some of the high-end stuff or kits from pre-2010. If your kit is from the past two years and is something you’ve picked up from your local PC store, chances are it will be around 1.65v by default (you can check this by looking at the sticker on each DIMM). Depending on the manufacturer and their binning process, this kit may be able to run far lower than the default voltage, or in some cases it may actually need a little more to run at the specified settings. This can be a problem for some 2,133MHz-plus kits.

Another important component to monitor when overclocking your RAM is your IMC. Should your IMC be overworked, it may also require a higher voltage in order to find stability. This is where CPU binning comes into play, as some CPUs will have far more tolerant IMCs than others. Your standard IMC on Intel Ivy Bridge should see you into the 2,300MHz frequencies with only a little voltage increase; however, some will struggle to break 2,400MHz no matter how many volts are applied to the controller.

The third subset of timings is important, though there are a few that can be left alone. The important ones would be tWWSR and TRRSR if you’re going to start playing around

On our ASUS motherboard, the IMC is called VCCIO. In order to push our RAM above 2,600MHz, we typically need to give it a boost. Check your motherboard manual if you’re not sure what your IMC is identified as in your BIOS.

INITIATE STABILISATION

It should be fairly evident when you’re overclocking if your current settings are stable, semi-stable or completely unstable. If your system is locking up at the Windows logo, you’ve got yourself an unstable overclock and you’ll need to tweak your settings further.

If you’re getting random lockups, or are locking up at a specific part of a benchmark, you’re going to be fairly close to a stable overclock. From this point onwards, it is important to only change one setting at a time and constantly check back for increased stability. For example, if loosening up one particular cache latency fixed the issue, chances are, as you push the kit further, that same timing will once again need to be loosened.

Depending on how far you want to take your kit, memory testing applications (such as MemTest) quickly become redundant. Once you’re running over 2,500MHz, chances are your system won’t ever be 100% stable, and such programs are only pointing out the obvious – that this system is now only good for quick benchmarks and not a whole lot else.

If you’re having trouble finding stability, try to resist the urge to simply brute force the chip with enormous voltages.  Take a few steps backwards to a BIOS save that you know works well (saving stable clock profiles is very important) or start again in a fresh profile. Don’t forget that the more RAM sticks installed, and the higher the density of your DIMM, will have an impact on performance, so don’t get too frustrated if you can’t break 2,600MHz CL9 on your new 16GB kit.

If you are after a bit of fun with RAM overclocking in particular, AMD’s Fusion series is actually rather entertaining. The IMC is surprisingly robust, and given the current and past success on the Belgian overclocking fanatics HWBot’s ladders (with the current record of 3,900MHz) we’d say it’s a good way to learn the ropes of RAM overclocking, and also understand the settings your RAM requires to be pushed to its limits before moving it over to an Intel IMC for other benchmarks. Another obvious bonus of the Fusion setup is the relatively small cost involved, should you have any breakages or want to change systems in the future.

It’s very important to save profiles for each of your RAM kits, if you don’t you’ll quickly forget which settings were required for each kit to function optimally.

BENCH TIME

The list of benchmarks we can run isn’t all that long when it comes to RAM overclocking. MaxxMem is officially supported by HWBot, though not many overclockers tend to use it, which leaves SuperPi and PiFast as some of our favorites, despite CPU speeds having a heavier influence on results.

Other recommended benchmarks are AIDA64 (Memory Suite) and Sandra 2012. However, given their slightly more complex software, they are more prone to crashes at high clocks when compared to Pi calculations.

Arguably, the most popular form of competing with memory overclocking would be for frequency records. This is fairly self-explanatory, and currently dominated by the AMD Fusion series. For these records the system does not actually have to be benchmark stable; only stable enough to POST, load Windows and capture a verified screenshot using CPU-Z.  Cache timings are not important either, so generally expect to see numbers around CL15 or so for most frequency records.

Here are the default selections for RAM frequency, this can be increased further on most boards by changing the BUS/CPU:RAM ratio.

And that’s all you need to know. Now go forth, and set some records!

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