How to Choose the Right Memory: A 2020 Guide To DRAM

The amount and specs of your system’s memory, or RAM, can make a significant difference, from the number of running programs (or just open browser tabs) that you can have open before your system starts getting sluggish, to the frames per second (fps) you can squeeze out of your CPU’s integrated graphics when playing the latest popular esports title.

If you’re shopping for some memory for a new build, or an upgrade to your existing laptop or desktop, and you’re confused whether you need 8, 16, or 32GB (or more), how much clock speed matters, or what memory timings actually mean, you’ve come to the right place. We’ll help you work through the many things to consider when shopping for RAM.

We’ll primarily be focusing on desktop memory here, although much of the advice and technical details carry over to laptops as well. With laptops, you’ll just have to buy an SO-DIMM (small outline dual in-line memory modules) kit, rather than the longer DIMMs (dual in-line memory modules) that are used in traditional modern desktops. Many modern slim laptops also have their memory soldered to the motherboard. So be sure to check your manual before making any buying decisions.

If you’re not sure exactly how much memory you need, the short answer is, considering common workloads and today’s pricing, that 16GB is the sweet spot. Content creators and enthusiasts heavily into multitasking may want to consider more. You can dive deeper into memory capacity considerations in our How Much Memory Do You Need feature.

For details on rated clock speed (measured in MHz) and timings (listed as a series of numbers, like 15-15-15-36), you can check our frequency and timings primer, were we also look at how the number of ranks (or banks of memory on a given stick or kit of memory) can significantly affect real-world performance. We’ll also detail many of these details and others below. But first, here’s a few key shopping tips in case you’re already in the store trying to figure out what to buy.

Quick Shopping Tips

• 16GB is the current sweet spot at today’s pricing. Gamers and those doing basic mainstream productivity tasks can get by with 8GB. But several open browser tabs and other running programs can use this up pretty easily. Given you can buy 16GB for as little as $25 more than 8GB, most should opt for 16GB. Those doing serious content creation will likely want more.

• Don’t pay for clock speeds your system doesn’t support. Memory speed is limited, particularly with some low-end and mainstream Intel CPUs and chipsets. So if, for instance, your system only supports 2,666MHz, there’s no point in buying RAM that’s rated for 3,600. You won’t be able to achieve the higher speed, and may wind up stuck at an even lower fallback speed. Check the motherboard manufacturer’s specifications for supported speeds and buy accordingly.

• Higher speeds have the most impact if you’re using integrated graphics. If you plan to game without a dedicated graphics card, you’ll get noticeably better frame rates if you opt for faster (supported) memory. But if you have to spend more on components to support that speed, as well as higher-clocked memory, it may make more sense to splurge on a dedicated card that will deliver a better gaming performance overall.

• Many programs and games don’t benefit heavily from faster RAM and better timings. The amount of software that sees major gains from faster, tighter-timing memory kits is actually fairly small. Some games will see a benefit, as well as compression software like 7-zip, as well as some aspects of content creation software. Do some research on the programs and games that you use most often. If you aren’t running memory-sensitive software and you have a dedicated graphics card, you can save some money by opting for slower RAM and spend that on a larger SSD or a better graphics card or CPU.

• Heat spreaders and lights are just for show. Generally speaking, most memory doesn’t run fast enough (unless perhaps you’re pushing it to extreme levels with manual overclocking) to require metal heat spreaders. So long as you have some air blowing through the case and over the memory, you can opt for bare sticks. Obviously, blinking lights won’t change your performance either. So if your case doesn’t have a window or you don’t care so much about how your memory looks, there’s no reason not to opt for sticks with exposed PCBs and memory banks--so long as it comes in the speed and specs you’re after.

XMP vs SPD

The technology that provides a motherboard with the correct frequency and timings is called Serial Presence Detect (SPD), and the part it’s detecting is a tiny ROM (read only memory) chip that’s been programmed with a timings table. Industry-standard timings are defined by the Joint Electron Device Engineering Council (JEDEC), an industry organization that includes companies from the memory controller and CPU industries down to DRAM IC manufacturers and assemblers. A list of approved DDR4 modes is frequently updated on Wikipedia. And for the most part, the associated timings for standard data rates are terrible and the optional “better” versions are rarely produced.

As explained in our How To Enable XMP, Intel’s “Extreme Memory Profiles” add an overclocking table to memory, occasionally pushed to the point that some of the fastest DDR4-4266 DIMMs have contained DDR4-2133 ICs. If your motherboard supports XMP, you can usually get a kit with a moderate data rate and tighter-than-standard latencies, such as DDR4-3200 CAS 14. The problem for those whose motherboards don’t support XMP is that these kits usually default to DDR4-2133 CAS 15.

Every current kit with enhanced timings requires XMP to automatically configure those timings, and the above-linked Wikipedia entry should help you figure out if those timings are standard or XMP. Those who chose not to take that risk may want to check out the CPU-Z screenshots of our memory reviews and pick from one of those kits.

How Many Modules?

You’ll need at least two modules to enable a dual-channel mode on platforms such as AMD’s Socket AM4 or Intel’s LGA 1151, or four to enable the quad-channel modes of AMD’s socket TR4 and Intel’s LGA 2066. Those modules could be single rank (with all ICs addressed by one of each module’s dual 64-bit interfaces) or dual-rank (addressed by both interfaces).

After tracking a similar phenomenon on Intel processors for several years, our Ryzen 3000 memory deep-dive detailed how having two ranks of memory per channel offers a significant performance benefit to some applications. We also know from our  PC Memory 101 article that two ranks per channel can be achieved by either doubling the number of modules or using modules with two ranks. Reasons to choose the later include leaving expansion room in the empty slots of boards that have two per channel, or getting the benefit of two ranks from boards that have only one slot per channel. Furthermore, while you may have read about T topography vs daisy chain in our comments or forum, you need not concern yourself with these concepts if you’re running only one DIMM per channel.

So, for the best performance,  opt for two modules for a dual-channel board or four for a quad-channel board. Those who can afford modules that have twice as many chips will benefit from both the extra capacity and a slight performance boost in certain applications. The recent re-introduction of 32GB desktop DIMMs means that you can even get 64GB from just two modules or 128GB from four, without worrying about whether your board supports pricier server memory. You’ll still want to check your motherboard manufacturer’s website to make sure that your firmware supports whatever capacity you’re using, though. You may need to update your BIOS first.

DDR4-2666 Is For Intel H/B Series Chipsets

Intel doesn’t allow overclocking on anything other than its Z-series (enthusiast) and X-series (high-end desktop) chipsets. That leaves mainstream buyers who don’t want to splash out for the Z-series other features stuck with Intel’s “approved” limits, including its DDR4-2666 maximum for Core i5 and higher processors.

We have reviewed several of these boards and noticed that most retail parts include Intel XMP. Even though this doesn’t affect maximum memory speed, it does enable one-click configuration of lower-latency DDR4-2666. Unfortunately, the market for low-latency DDR4-2666 is so small that CAS 12 and CAS 13 kits are no longer being produced. CAS 15 timings appear to be the quickest of currently-available parts.

DDR4-2400 Is For Intel’s Core i3 and Below

Intel’s low-end processors have the same chipset-based restrictions as we mentioned in the previous paragraph, but at an even lower DDR4-2400 data rate. The market for enhanced-performance memory at this data rate is so small that the lowest latency we can find among current products is CAS 14.

DDR4-2933 Is a Problem Solver

The beauty of DDR4-2933 is that it runs at a whole ratio, 11x133.333, which happens to be a lower ratio than the 15x100 that DDR4-3000 uses. We’ve seen a few boards that would run no higher than this, including Biostar’s award-winning X470GT8. Because it worked so well, memory at this data rate was widely available at CAS 15.

But then a rumor started floating around that DDR4-3000 was the sweet spot for 2000-series Ryzen processors, and manufacturers quickly began programming these modules to DDR4-3000 to meet the new demand. A limited variety of overpriced DDR4-2933 CAS 16 kits remain, though users who aren’t afraid to experiment can always revert their cheaper DDR4-3000 CAS 15 kits to DDR4-2933 if the higher data rate isn’t stable.

Ryzen Restrictions

By default, the memory controller of X570 motherboards switches to half-speed and the “Infinity Fabric” interface to an unsynchronized ratio when exceeding DDR4-3600 speeds, causing performance to drop when using DDR4-3733 or above. Many end users are reporting limits between DDR4-3733 and DDR4-3866 after disabling these stability protections, but that minor increase in data rate probably isn’t worth your effort, unless you’re just looking to achieve higher speeds for bragging rights.

Our motherboard guides detail the frequency capabilities of at least one configuration for each board we’ve tested, but we can’t test everything. For a quick-and-dirty look at the current memory landscape, here’s a chart of the currently readily available RAM kit capacities and types, along with the types of systems for which they work best. Price ratio is based on the cheapest kit in each configuration.

Performance Rankings, Best To Worst

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