The Memory Buyer's Guide: What's the Best RAM for My System?

Maximum PC Staff

Not sure what kind of memory to put in your new system? Ask MaximumPC.

A few months back, Loyd Case answered the popular question, “Which Video Card Should I Buy?” Needless to say, his story caused a considerable lull in video card related questions from our readers, letting a new topic take the lead: RAM. How much do you need? How fast should it be? Are latencies important? Today, we’ll be covering everything you need to know to get the right RAM for your system.

The Importance of RAM

Did I mention that this is going to be an all-encompassing guide on RAM? No? Well it is, so those of you who already know what RAM is for and how it works can skip ahead.

RAM stands for Random Access Memory and it stands as somewhat of a buffer between your hard drive and your CPU. There’s really nothing random about it; the CPU (generally) knows exactly what data it’s playing around with. When the CPU is processing data, it’s grabbing small bits in your systems memory, constantly jumping from place to place, reading, writing, and rewriting information. Hard drives work well when working with large blocks of data, but are extremely slow when jumping from sector to sector or switching from read to write. If your CPU had to process data directly on the hard drive, there would be a massive bottleneck.

So that’s why you need RAM. Having more RAM means you need to read from the excruciatingly slow hard drive less often, and faster RAM means your CPU can grab its bits faster. Of course, this still doesn’t answer how much RAM you need or in what circumstances faster RAM is actually useful.

How Much Memory Do You Need?

There’s really no such thing as too much RAM, but there is such a thing as spending too much on RAM. What you do with your computer is what dictates whether or not more memory is actually practical. Below are some of the key stepping stones when it comes to how much memory a system needs.

IBM’s latest supercomputer Watson has 16TB of RAM. Overkill?


There is such a thing as not enough RAM, and anything below 2GB is bordering on just that. In fact, the 64-bit version of Windows 7 won’t even install on a system with less than 2GB of memory. Now, that’s not to say 2GB isn’t enough for anything. Your every day computing tasks, such as web browsing, editing documents, and even HD video, will be fine on such a system, so long as you’re not doing all of it at once.

G.Skill's balance of performance and value makes it a popular brand.

Running on just 2GB does have some limitations, though. Ever since Windows Vista, we’ve had a tool called SuperFetch which pre-loads your most used apps into memory so that they open faster when you need them. Windows likes to keep about half of your total memory free, using the rest as SuperFetch space. Small problem: with just 2GB of RAM and essential operating system resources taking up about a gig of memory to begin with, it doesn’t leave much space for SuperFetch to use.

Things will still run just fine, but additional RAM will give a large jump in performance, and at the current prices, stepping up to 4gigs is a pretty worthwhile investment. Apart from netbooks, you’d be hard pressed to find anything modern that comes with just 2gigs of memory anyway.


When it comes to a balance of cost and performance, 4GB is just about perfect, at least for the time being. In every day computing, you probably won’t ever come close to filling it all up – well, unless you’re like me and have a nasty habit of leaving 116 tabs of Flash rich content open in Chrome.

Crucial is a very popular brand amongst hardcore gamers.

Even high-end gaming performs well with just 4GB of memory. Feel free to enjoy a casual bit of Photoshop and/or video editing, too. Apart from some very purpose specific computing, like extensive hi-res photo editing or industrial grade 3D modeling, 4gigs is the number to aim for.


Stepping up to 8gigs can still be practical, especially when building a new system in which the additional investment would be fairly negligible. Any performance increases in going from 4 to 8GB won’t be particularly noticeable, but it does open up a few doors.

Unless you partake in very specific computing practices that can actually fill up the entire 8gigs, you can go ahead and disable your pagefile entirely. This will give you slight performance increases under certain circumstances, improve your system’s security, and put less strain on your hard drive.

Kingston has been in the game for years and has a wide selection.

From a gaming perspective, putting 8gigs of memory into a system is primarily a form of future proofing; however, in a professional environment, as a workstation running commercial grade software, 8GB may very well be necessary to keep things running smoothly.

3, 6, AND 12GB

You may have noticed the absence of any recommendations relating to 3, 6, and 12GB solutions. That’s because achieving 6GB of RAM, for example, requires an odd combination of DIMMs (memory sticks). In this example, you would need three 2GB DIMMs, meaning you would not be able to run them in a Dual Channel Configuration.

Dual Channel memory allows the CPU to access both DIMMs simultaneously, essentially turning the 64-bit memory bus into 128-bits. As far as gaming and your average computer use is concerned, dual channel and single channel configurations will perform almost identically, but any memory intensive operation, such as audio or video transcoding, will see significant improvements.

Corsair has always been one of our favorite memory brands.

In order to enable the dual channel memory bus, you need an even number of identical DIMMs, which is why 3, 6, and 12GB won’t work; however, unless you plan on doing a lot of memory I/O intensive work, the performance benefits of more RAM generally outweigh the benefits of the larger memory bus.

There is one exception – triple channel memory. In the case of the LGA1366 Core i7, memory can be configured into a triple channel bus using three identical DIMMs, meaning 6 and 12GB are much more practical.

What about Speed and Latencies?

So you’ve figured out how much RAM you need, but how fast should it be? Well, for the best results, it should be as fast as your motherboard allows. This would be for anyone who wants to be on the bleeding edge of performance, like a hardcore gamer. The average consumer won’t have much need for the fastest RAM in the world, and that stuff can get pretty expensive. Instead, DDR3-1600 is a nice middle ground. It’s still fast, but not so fast that it costs a hefty premium.

But wait! Before you run down to the store and fork over all of your hard earned money for fastest rated RAM you can find, there’s one more thing to consider: Latency. Memory modules are also rated in “Timings,” generally a sequence of numbers, such as 9-9-9-24. The most useful of these is the first number known as the CAS Latency. This is the number of clock cycles it takes the RAM to access a column of data (the smaller the better), and in conjunction with the speed of the RAM, can be used to calculate its response time. The formula is

1000 * CAS
(RAM Speed ÷ 2)

This will give you the response time in nanoseconds. So for example, a certain DDR3-1866 module of Kingston HyperX memory has a CAS latency of 11 while G.Skill makes a DDR3-1600 module with a latency of just 6. The result? G.Skill’s slower RAM can respond in just 7.5ns where it takes the much faster HyperX RAM 11.7ns. This means that the G.Skill memory will be faster when it comes to random access; however, the higher clock speed of the HyperX memory still nets it more bandwidth, making it better suited for bulk operations.

Typically speaking, you want to settle on a clock speed first and then use CAS latencies to decide from there. Keep in mind that tighter timings mean more expensive. For instance, the difference between a CAS of 7 versus 8 is almost negligible.

System Compatibility

When it comes to RAM, there are a lot of questions regarding compatibility. There are also a lot of subtleties that can go overlooked and lead to compatibility problems. These are a few of the most common questions and mistakes.


The different memory types have different pin configurations.

YES! DIMM design is different between all three DDR standards. Not only will a DDR DIMM be incompatible with a DDR2 system, but it won’t even fit in the DDR2 socket. Trying to force it in could break your motherboard. Fortunately, DDR and DDR2 platforms are pretty much extinct. If you have a modern computer, odds are it’s DDR3.


DDR and DDR2 SO-DIMMs have the same pinout, but are not cross-compatible.

A SO-DIMM is a miniaturized version of a regular DIMM, generally used in laptops and other low profile systems. Just like a full sized DIMM, it’s important not to mix up DDR, DDR2, and DDR3 modules.


Kind of, though it can be a gamble. Memory modules have an internal table of speed and timing settings so when you install a module that is clocked higher than your motherboard is rated, your motherboard will simply run it at a slower speed. For example, if you put a DDR3-2000 DIMM into a DDR3-1600 motherboard, it would run at 1600MHz rather than 2000MHz. Compatibility isn’t guaranteed, though, and it’s typically better to match your RAM with your system’s capabilities.

This trick is, however, useful when overclocking. Because memory clock speeds are derived from the CPU’s FSB, using the faster memory can result in a more stable overclock.


Memory voltages are actually very important when it comes to compatibility. The DDR3 standard is 1.5V, but many performance DIMMs require higher voltages to achieve higher clock speeds and lower latencies. This can cause problems as not all motherboards can recognize the proper voltage for these DIMMs and will supply the default 1.5V. If this isn’t enough to keep the memory stable, your system won’t even boot up enough for you to get into the BIOS and manually raise the voltage. Make sure you’re familiar with your motherboard’s capabilities before purchasing RAM with increased voltage needs.


32-bit operating systems offer one last serious limitation in that they can only address about 4GB of memory. You may think that’s perfect since 4GB is currently ideal, but the limitation is on total memory, not just RAM. A few bits here and there are reserved for PCI and ACPI peripherals, and video memory is included, too. With modern video cards sporting up to 2GB of video memory, you could have 4gigs of RAM in your system yet be stuck running on less than 2GB. The moral of the story is stick with a 64-bit OS.

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