Fall 2009 Memory Buying Guide
I had recently done an article on the History of RAM, and promised to follow that up with a detailed buying guide. My aim is to layout a basic idea for anyone who is in the market to buy memory for a new build but this guide would equally be helpful for those who want to put some muscle into their existing machine. I’d be making suggestions based on the type of CPU/chipset you have, so make sure you know what you are running under the hood.
Also it would be helpful if you know details about your operating system, like what is the maximum amount of memory it supports. So lets get started with the guide.
First things first, what operating system are you using? Most of you would be running a version of Microsoft Windows. But each has their own memory requirements, so your buying decision should be based on that. Here is a quick information table for most popular versions of Windows.
|Operating System||Minimum RAM||Maximum RAM*|
|Windows XP 32-bit||256 MB||3 GB|
|Windows XP 64-bit||256 MB||8 GB|
|Windows Vista 32-bit (All SKUs)||512 MB||3 GB|
|Windows Vista 64-bit (All SKUs)||512 MB||8 GB|
|Windows 7 32-bit (All SKUs)||1 GB||3 GB|
|Windows 7 64-bit (All SKUs)||1 GB||8 GB|
Now most of you would be wondering what that (*) is for? Its there to highlight the fact that I’m listing the maximum memory that you should have for the selected operating system. Even though 64-bit versions of Windows can access a lot more memory, 8 GB the maximum amount you should be aiming for which is more than enough for everything (unless you work at a Movie/TV studio and have to work on a lot of HD content in parallel).
DDR2 vs. DDR3
A lot of debate these days is usually done on the value of DDR2 vs. DDR3. You’d already know about the technical differences between the two if you’re read the previously mentioned history lesson. In short, DDR3 improves upon DDR2 by allowing much higher clock speeds but more sluggish refresh rates. This essentially leads to a nearly negligible difference in real world performance. Though the prices for DDR3 have dropped a lot in 2009, and in some cases are nearly the same as DDR2. Plus DDR3 has an added advantage of having lower operating voltages and are more energy efficient.
But the decision on which component you drop into your rig should depend upon your chipset and CPU. If your CPU/motherboard only support one of the standards (DDR2 or DDR3), then you really don’t have a choice here. Though if they have support for both, I’d suggest that you stick with a higher DDR2 which would run you the same amount of money as a basic or mid range DDR3 kit. The following table sums it all up.
|Processor Line / Socket||RAM|
|Core 2 Duo||DDR2|
|Core 2 Quad||DDR2 or DDR3|
|Pentium Dual Core (Intel Core)||DDR2|
Single Channel vs. Dual Channel vs. Triple Channel kits
There really isn’t much of a choice here either. You should most definitely stick to whatever number of channels your motherboard supports. Single Channel boards are a rarity these days, while Triple Channel is only for Intel LGA-1366 based Core i7 chips. Everything else has Dual Channel memory. I’ve seen a lot of people going with single RAM modules instead of Twin-kits or Tri-kits because they are a bit more cheaper.
But I would discourage buying a single module when your board supports multiple channels because it would improve performance. The only reason for buying a single module could be that you are replacing a damaged part or adding another one. If its the later, then make sure you complete your channel pairs i.e. if you already have two modules in a Dual Channel setup and plan to add more memory, then throw in a twin-kit instead of a single module.
Clock speeds are an important factor in determining performance of your components, though contrary to popular beliefs, higher speeds don’t always mean higher performance (if the underlying technologies are different). Even if you are running on the same technology, higher clock rates may still bring lower performance if you don’t keep other parameters in check, like refresh latencies and timings.
As a rule of thumb, you should get the maximum clock speed possible from your CPU/Northbridge bus. While it still would be possible to get higher clock rates via overclocking, you wont really gain any real world performance once you try to go over the max limit possible on your hardware.
Memory Timings and Latencies
Memory Timings are just as important as clock speeds – a fact which most average users tend to ignore. However, there are technical limitations imposed on these speeds by other components, like the clock rates and memory size. The larger the size of the memory, the longer would be the latencies. Same principle applies to the clock speeds as well, so it is very important to find the sweet spot here.
More aggressive timings would draw a lot more power compared to loose ones, so you should also keep your power requirements in mind especially if you’re on a battery powered machine. The following table lists what cycle latencies you should look for with respect to their clock speeds.
|DDR2 800 MHz||4-4-4-12|
|DDR2 1066 MHz||5-5-5-15|
|DDR3 1066 MHz||7-7-7-20|
|DDR3 1333 MHz||7-7-7-21|
|DDR3 1600 MHz||8-8-8-24|
|DDR3 2000 MHz||9-9-9-27|
There are several other features you might want to bring into consideration while buying memory modules, but keep all these on lower priority levels than the above mentioned parameters.
You may have read these terms a lot on spec sheets from different memory modules. Registered memory helps in detecting errors during data transfer to and from the memory. ECC also adds the ability to correct those errors detected by the parity checks. Modules with these capabilities have 72-bit lanes instead of normal 64-bits, but they are only useful in servers because of their added weight into the price tag. A normal desktop user can easily do without them.
Heat sinks and spreaders are very important for keeping the memory cool under load. Almost all memory modules come with a heat spreader even its really small. There are some premium kits like the Corsair Dominator series which have larger heat sinks (and even cooling fans) but they are only useful if you plan to do heavy overclocking. The average Joe won’t ever need them.
I’d like to conclude this guide by asking for your input and feedback. I tried to cover all the basics (as well as some advanced stuff) you need to check while buying memory but I might have missed something. But that is where you guys come in, so please comment to share your thoughts. I’d also love to hear what articles you guys would like us to do in the future.