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Step 5: Select Memory

How To Build A PC: From Component Selection To Installation
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There are a ton of options when it comes to system memory. From data rates to latencies to voltages, the number of combinations can become overwhelming. The easiest answer in the debate of what kit to buy sounds deceptively simple: just buy 1.5-volt DDR3-1600 (PC-12800) modules with CAS 9 timings. All Socket AM3+, FM2+, LGA 1150, and LGA 2011 processors are designed to support at least this memory speed. It's inexpensive as both 4 and 8 GB sticks, and it’s available in both dual- and quad-channel kits.

Yet there are noticeable performance benefits for similarly-priced DDR3-1866 (PC3-14900), particularly if you're using a CPU's on-die graphics engine for gaming. And this speed functions normally, even with processors that are not officially designated to use it (primarily older models or low-energy platforms). And the same easy benefits of DDR3-1866 are even available with most DDR3-2133 kits and modern performance-oriented processors.

The problem with recommending faster memory kits is that they often require at least some manual configuration. If you're not comfortable tooling around in your motherboard's firmware, they might actually drop you to lower performance levels.

You see, Intel’s XMP (eXtreme Memory Profiles) technology facilitates extended memory settings beyond the basic automatic-configuration technology called SPD. Though XMP originally allowed motherboards to set overclocked options like nonstandard voltages and data rates, most of today's XMP-capable modules operate at standard voltage levels and frequencies. Still, when you first boot up, they typically default to either DDR3-1333 or -1066. Going higher requires that you manually enable an XMP profile. Even some DDR3-1600 modules employ XMP (rather than SPD values) to achieve their rated performance levels, and this is particularly true of reduced-latency (CAS 7, CAS 8) modules.

Memory faster than DDR3-2133 is usually expensive and not really required. Our tests have shown that DDR3-2400 is barely beneficial, and only in situations where you're leaning on integrated graphics. We've even seen data rates above 2400 MT/s hurt performance as the motherboard attempts to increase stability.

In terms of memory quantity, Tom's Hardware recommends at least 4 GB for the cheapest Web surfing Windows-based systems. Gamers could probably get by with 4 GB, but we’re more comfortable with the 8 GB that has become the norm in high-performance machines. Few applications push memory needs past that point, though users of memory-intensive programs who also multi-task (such as Tom’s Hardware editors) can occasionally find an excuse to install even more. Users who need more than 8 GB usually know their needs in advance, based on experience with a previous machine.

Even those exceptional circumstances only push us to 12 GB, though 16 GB is easier to install in dual-channel mode (via two 8 GB modules). If you’re desperate for an excuse to add even more, installing RAM disk software (which uses some of your system memory as a virtual hard drive) could be your impetus.

Our memory reviews show a wide range of options, and buying name-brand modules with lifetime warranties from reputable venders is good insurance against unexplained system instability.

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