How Does RAM Speed and Timing Affect My PC’s Performance?

By Michael Crider on April 19th, 2017

When it comes to computers, more is better. Well, sort of. Most users understand that a faster processor, with speed expressed in megahertz or gigahertz, is more desirable. Likewise, it’s fairly obvious that having more gigabytes of memory (aka RAM) is a good thing. But your RAM has another stat you might be confused about: speed.

So, what does that speed rating on your RAM actually mean? The answer is simple, but how it actually relates to your system performance is complex. In a nutshell: it’s probably less vital than the RAM manufacturer would like you to believe.

What RAM Speed Ratings Mean

The speed rating of your RAM module is an expression of its data transfer rate. The faster the number, the faster your computer can store and retrieve the data stored in local memory. The formula for the exact speed rating changes slightly based on the version of DDR memory your computer is using (see below). It’s no longer simply an expression of clock speed, like a processor, but a combination of hardware factors. But in general, faster is better. Pretty simple, right?

Things start to get complicated in the nomenclature. Though the speed rating is usually expressed in straight “DDR” terms, we also have the old PC2/PC3/PC4 standard still hanging on. These numbers generally follow the speed rating corresponding to the generational standard: “DDR3 1600 RAM” is also labelled as “PC3 12800,” “DDR4 2400 RAM” is also “PC4 19200,” and so on.

This is a technicality based on the old bit and byte data expression—one byte equals eight bits. So, if the first number is DDR 1600, expressed in million bytes per second capability, the second number is PC3 12800, expressed in million bits per second. 12800 divided by eight is 1600, so it’s two ways of stating the same thing. Generally, things will be less confusing if you stick to the first “DDR2/3/4” speed rating.

What RAM Timings Mean

In addition to standard speed ratings, each RAM module also has a rating for something called timings. This is expressed as a series of four numbers, like 5-5-5-15 or 8-8-8-24. We’re getting into some advanced computer science topics here, dealing with the specific amount of time it takes the module to access single bits of data across columns and rows of the memory array. But for the sake of brevity, this collection of numbers is generally referred to as “latency.”

Latency deals with how fast the RAM module can access its own hardware, and in this specific case, the lower the numbers, the better. Lower latency means faster data access, thus faster data transfer to the CPU, and faster operation of your computer overall. Higher-quality, more expensive RAM has lower latency, and both this rating and the RAM’s clock speed can be overclocked by enthusiasts.

That being said, the differences in latency are so minuscule that unless you’re running industry-level server operations or multiple virtual machines, you’re unlikely to see any real difference between RAM with a higher or lower latency.

But What Does All This Do for My PC?

Honestly, it doesn’t mean a lot. While faster, lower latency RAM will indeed increase the technical performance of your computer, it works at such a fundamental level that it’s almost impossible for us flesh-and-blood humans to actually appreciate the difference. It’s like the comparing Data from Star Trek and C3P0 from Star Wars—if one can calculate the odds of survival in one billionth of a second and the other takes two billionths, does it really matter which one you ask?

Faster RAM will give your PC better performance in certain specific benchmarks, but in terms of actual benefit to most users, having more RAM available is almost always better than having faster RAM. So if you’re on the fence about purchasing 8GB of DDR4 RAM with a speed rating of 3200 or 16GB of DDR4 RAM with a rating of 2400, go with the second option every time. It also means that overclocking RAM in the system BIOS is rarely worth the effort.

This is especially true for gaming. If your computer has a discrete graphics card, then games will rely primarily on the video card’s own memory (labelled as “GDDR,” specifically designed for visual applications) to handle these functions. Note: since your graphic’s card’s memory is mounted directly onto the graphics card PCB, it can’t be upgraded by the end user. Again, choosing a card with more memory is generally better than one with faster memory.

Graphics cards include their own memory, so games aren’t majorly affected by system RAM speed.

Faster RAM can help visual performance with computers that use an integrated GPU, like Intel’s non-discrete designs or AMD’s Accelerated Processing Unit series. That’s because this setup relies on system memory for graphics performance. It can also make a more obvious difference for machines that are constantly accessed from multiple points, like a high-traffic web server or a virtual machine host. But for most users, it just isn’t a big deal.

DDR2, DDR3, DDR4, and Speed Compatibility

RAM comes in different generations, with updated standards allowing faster and faster access to the data stored in memory. The original DDR standard—short for “Double Data Rate”—succeeded Single Data Rate RAM way back in 2000, and we’re currently on DDR version 4. DDR3 RAM introduced in 2007 is still used in older or cheaper PCs.

Each successive version of DDR increased the memory bus and speed capabilities of the RAM module format, leading to increased performance. But what’s really important to remember is that the standards are not backward- or forward-compatible. If your laptop or motherboard is rated for DDR3 memory modules, it can only use DDR3, not DDR2 or DDR4. The physical slots for the different standards don’t even match, so it should be impossible to install the wrong DDR standard anyway.

Note the different pin configurations on DDR3 and DDR4 RAM.

That’s not the case with speed ratings, however. A motherboard’s RAM slots can operate at speeds below their maximum without issue. So if your motherboard accepts DDR4 RAM at up to 3600MHz, but you’ve found a sweet deal on modules rated for a maximum of 2400MHz, feel free to install them.

Also note that your motherboard may not run your RAM at its advertised speed out of the box. If you buy DDR4-3600 RAM and your motherboard supports anything up to DDR4-3400, it may still clock it to the lowest setting by default—say, DDR4-3000. You’ll want to head into your computer’s BIOS and set it to the correct speed, either by enabling Intel’s extreme memory profile (XMP) or by adjusting the speed yourself.

Also note that installing non-matching RAM DIMMs (which have different speed and timing ratings) is generally OK—your motherboard is smart enough to handle the different hardware. But in each case, the system will clock down to match the slowest memory module it has access to, so buying faster RAM to mix with slower RAM doesn’t have any real benefit. Where possible, it’s best to match new RAM with old RAM.

Image Credits: NeweggGskill, GB Public PR/Flickr, Corsair

Michael Crider has been covering technology on the web since 2011. His interests include folk music, football, science fiction, and salsa verde, in no particular order. He wrote a novel called Good Intentions: A Supervillain Story, and it's available on Amazon. You can follow him on Twitter if you want.

  • Published 04/19/17
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