DDR3 memory: everything you need to know to upgrade

11th Jan 2009 | 09:30

DDR3 memory: everything you need to know to upgrade

The complete guide to DDR3 RAM

PC technology is cyclical, and every time a new one comes along, it means another trip to the bank manager to explain why we need a higher limit on our credit cards.

When DDR3 was first released, you'd have thought it was handcrafted from a block of solid gold it was so expensive.

While the price isn't high enough to make King Solomon blush anymore, it's still a fairly hefty investment. If you're spending so much, you want something to show for your money, but memory performance is harder to quantify than CPU or graphics chipset performance.

If you're planning on upgrading to Intel's new Core i7 micro architecture, then DDR3 is going to be an essential part of your system, but even for those sticking with P45, DDR3 is still very much a requirement.

This article isn't about how much better DDR3 is than DDR2, it's more about how much you should be paying for your RAM, and how much you should install. We've always said fit as much as you can afford, but with Vista's overheads, that has slowly crept up. Now 4GB is a requirement for high-performance gaming.

Of course, if you're using a 32-bit OS, as a vast majority of people are, XP can only use 4GB, due to the limit in address spacing. In practice, however, the amount of RAM that Windows will actually use is closer to the 3GB mark.

Losing half a gig, when it's DDR2 isn't so bad, but when you're paying a premium for DDR3, you'll want to make use of every last byte. On our test machine, only 3.24GB was available to Windows, which, when you're paying up to £250 for the privilege, is galling.

The answer, of course, is to switch to a 64-bit OS, which has no such memory restriction. While there are plenty of free, 64-bit Linux distros, it's not a path we'd recommend unless you enjoy trying to solve compatibility issues.

While some games are quickly ported to Linux, many aren't and you'd end up having to use something like Crossover gaming, which is far from ideal. XP is now end-of-life and although you can still find copies of Windows XP-64 for sale, it lacks drivers. This leaves you with Vista 64-bit, but before you hold your head in despair, let us allay your fears.

Although Vista was pretty horrible when it was first released, through the addition of numerous patches, updates and Service Pack 1, the OS is much improved. Unlike the strangled birth of Windows XP-64, Microsoft has been pushing manufactures and developers to support Vista 64-bit from the start.

There are now plenty of drivers available, and while the number of native 64-bit apps and games is still low, at last there are no major concerns with memory management. Installing Vista 64-bit will require a clean install, but the good news is that if you have a copy of Vista 32-bit, you should be eligible for a free upgrade.

Check the details by going to www.microsoft.com/windows/windows-vista/get/upgrade-advisor.aspx. If you're running XP, then you can get an upgrade to Vista 64-bit, but you'll need to pay for it, although it will be less than buying a brand-new copy.

Of course upgrading to Vista 64-bit will, undoubtedly, bring some headaches. Chief among these will be driver issues. Support for 64-bit driver's in Vista is far better than it ever was in Windows XP 64, but there are still a number of manufactures who haven't seen the need to write the appropriate drivers.

While you're mostly guaranteed to be able to find drivers for your mobo chipsets, graphics and sound cards, you may find other, older hardware, such as printers, scanners and even programmable keyboards and mice are incompatible. So, before you take the plunge, find out if you'll be disabling half of your hardware.

Ramming it home

But enough talk of bits and bytes, what will upgrading to 4GB or more actually do for your gaming? Well, you shouldn't expect to see massive increases in frame rates, because, in most cases, the vast majority of the work is being done by the graphics chip and CPU.

Games are memory intensive, but it's unlikely that you'll be doing anything else at the same time; such has opening hundreds or browser tabs, or reading your email, unless you're AFK-mining in EVE Online perhaps, so your game will usually have almost exclusive access to your RAM.

You'll see plenty of demos of HD movies being rendered, while simultaneously shooting zombies, and emailing YouTube clips to their friends, but back in the real world, this sort of thing doesn't happen.

However, any game that loads a lot of textures, is going to appreciate having some extra RAM to play with. Scrolling round a Company of Heroes map, with all the detail turned up, you'll soon appreciate the difference between 2GB and 4GB of RAM. If you run your games windowed, then you'll need as much RAM as you can get, especially in Vista with Aero running in the background.

RAM is just a temporary storage area, so anything that requires loading, including the game itself, and new maps or levels, will benefit from having more RAM to play with, but don't forget, your hard drive still has the potential to be a bottleneck in the system.

Still, the more information that can be loaded into RAM, the less needs to be pulled off the disk. Of course, you may find that the frame rates on some games do improve but you'll be looking at fairly small changes, not an excuse to put off upgrading your poor, over-worked graphics card, though.

Number crunching

DDR3 comes in a range of speeds, from 800MHz, up to 2,000MHz, but compared to DDR2 has some fairly high latencies.

While a typical DDR2 module may have timings of 5-5-5-15, you can see that our test samples have timings much higher, such as 9-9-9-28. Still because the clock cycles are shorter than DDR2, the effective latency is lower than might be suggested.

As with DDR2, there's a whole new set of numbers to learn, with modules named after peak transfer rate, rather than the bus speed. So, DDR3-800 which has a peak transfer of 6,400Mb/s is DDR3-6400, while DDR3-1600, which has a peak transfer rate of 12,800Mb/s is named DDR-12800, simple, no?

While modules in the 800-1,600MHz range are part of the JEDEC (Joint Electronic Device Engineering Council) spec, there are now modules that operate at 1,800 and 2,000MHz. However, because many mobos lock the memory clock to the CPU, it's not always possible to get them running at this speed.

Depending on your BIOS settings, you may be able to force the board to use certain speeds. For instance, on one board, the options were 800, and 1,066, unless we turned overclocking on, which then gave us access to 1,333 and 1,600. Even so, the Core i7 board using the X58 chipset still wouldn't allow us to set the memory clock to 1,800 or 2,000, so the maximum speed we could run them remained 1,600MHz.

Although Core i7 now has the memory controller on the CPU, vastly increasing memory bandwidth, you still may not be getting the maximum speed out of some modules. On a P45 board, you'll need to find out how far you can crank the memory clock to, before you drop wads of cash on top-end DDR3.

Ramming speed

Of course, Core i7 has not just given us a new memory controller, the X58 chipset allows you to run dual or triple-channel setups. This opens up the potential for 6GB or even 12GB setups, if you have very, very, deep pockets.

Such a vast amount of RAM potentially does away with the need for an old-fashioned swapfile and you'll probably even hear some memory companies advising it.

However, we'd recommend you don't go disabling the swap file just yet. While it's going to take a fair amount of effort to fill up 6GB, should Windows need to use the swap file, and you've disabled it, you'll be in for an unpleasant surprise.

So, is it worth upgrading to the fastest RAM money can buy? While you can get DDR3 at speeds of up to 2,000MHz, there are a couple of issues you need to be aware of.

First, it's unlikely that you'll be able to buy a 4GB kit at this speed; our review samples were only available as 2GB kits at 1,800 and 2,000MHz. Second, unless you have an Extreme Edition Core i7 CPU, you're unlikely to be able to run the memory clock much above 1,600MHz.

In our tests, running the higher speed memory at 1,600MHz, instead of its rated speed, ended up giving some lower throughput figures than other memory run at the correct speed. There's no doubting though, that triple-channel rules the roost.

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First published in PC Format, Issue 222

Now read How to get the best from the Windows 7 Beta

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