Corsair Dominator 6GB 1866 MHz DDR3 review

Product:	Dominator 6GB PC15000 DDR3 RAM Tri Channel, 1866MHz, DHX
Manufacturer:	Corsair
SKU code:	TR3X6G1866C9DF
Information:	website
Street price:	449 USD

Bringing the TRI into your PC

What would you say is the biggest product release last year that opened up a can of performance in it's own segment ? Yeah .. it just has to be anything Core i7 related. The processors series rocks, the mainboards are expensive yet fantastic, and another thing it did and will continue to do so .. it drives sales of (and the move towards) DDR3 memory upwards.

It's quite interesting to see what the release of a new processor architecture can achieve. If anything the release of Core i7 has shown us that with a standard FSB based and clocked PC, the memory was extremely underappreciated until you started to overclock that front side bus.

DDR3 memory has become a every important and integral part of the Core i7 eco-system and obviously memory vendors jumped on that. Though not at all required for Core i7, it does offer you the option to go for Triple channel memory, instead of dual-channel memory. Smashing even better memory performance and bandwidth smack down on the table. And that's a good opportunity for everybody. The memory manufacturers, and you as a consumer as well.

Therefore a lot of triple memory kits are now available on the market ranging in a plethora of clock frequencies and sizes. Most popular are of course the 3 and 6 GB kits. And as you guys know, we test a lot of games .. this year for the first time I am advising people that move towards such a high-end system to make the move for 6GB memory as well. See, though very limited right now, we did run into some game situations where the difference between 3 and 6 GB was measurable, and most of all noticeable.

One of the leading manufacturers out there is of course Corsair. A brand with reputation to uphold, they are strong in the high-end market and are focused and dedicated to keep it that way. It came as no surprise to see them release some pretty dandy kit onto the market. One of these kits is a 6 GB (3x2GB) 1866 MHz Triple Channel memory kit at CAS latency 9, it's available under SKU (product code) TR3X6G1866C9DF and comes with a Dominator airflow fan. To date this is the most impressive six Gigabyte memory kit we have had our hands on. So please head on over to the next page, where we'll startup a review on this amazing memory kit and look at both performance and aesthetics.

A swift 101 on system memory

How does RAM memory actually work ?

Adding RAM (random access memory) will normally cause your computer to feel faster on certain types of operations. Some applications (think Photoshop or most movie editing and animation packages) need bags of RAM to do their job. If you run them on a PC with too little RAM you'll see Hard disk swapping / activity constantly brining he system down to a crawl. It as at that tim that you can get a massive speed boost by adding enough RAM to eradicate the swapping. Programs like these can seriously run 10 to 50 times faster once they have enough RAM.

But how does RAM work ? Well, the essence is actually very simple, we live in a digital world with 0's and 1's.To store a 1 in the memory cell, a capacitor is filled with electrons. To store a 0, it is emptied... that's it... it's that simple.

The dilemma with the capacitor's container is that it has a leak. In a matter of a few milliseconds a full bucket becomes empty. Therefore, for memory to work, either the CPU or the memory controller has to come along and recharge all of the capacitors holding a 1 before they discharge. To do this, the memory controller will read the memory and then writes it right back. This refresh operation happens automatically thousands of times per second.

Dual Channel memory ?

Typically you guys make sure that you buy two bars so that you can have a dual-channel memory configuration (color coded identically on your mainboard). Dual channel effectively double's the memory bandwidth and processors loves that bandwidth, for sure, as it can have a nice impact on overall performance.

So keep this in mind: performance and stability of any system depends in part on the memory being used and the settings for the RAM timings. Many users may have their preference for low-quality class-B brands; but certainly using brand name memory is a very good idea since low quality memory is often at the root of many stability issues. However, always pay attention to the timings of the memory being used.

Triple Channel memory ?

With the coming of Core i7 we've seen the integration of on-CPU integrated memory controllers for DDR3 SDRAM with 1 to 3 -- 64-bit memory channels (physically four only three active though). You read it right, a tri-channel memory controller. Therefore total memory bus width goes up from 128 bits to 192 bits allowing a massive bandwidth increase as they are no longer tied to the FSB. Intel eliminated those "FSB brakes" by designing Nehalem's architecture to use 64-bit memory controllers which are connected directly with the processor's silicon. As a result this new design should bring a bandwidth utilization of as much as 90%, a nice jump from today's 50-60% utilization for sure. The new controller of course supports both registered (server market) and unregistered (consumer) memory DIMMs. The controller is fast ... very fast, and supports DDR3-800, DDR3-1066, DDR3-1333 JEDEC standards, yet has room for future scalability. The memory controller is able to handle 64GB/s, a full tri-channel DDR3-1333 implementation will only amount to 32GB/s maximum bandwidth utilization.

Do the math and conclude that even DDR3-2000 will not max out the controller.

So then, three memory channels per processor, each channel supports a maximum of 3 DIMMs. Again do the math and a single processor can support a maximum of 9 memory slots. You are of course free to use one or two DIMMS, but for optimal performance, the minimum would however be three, one DIMM per channel. So depending on the motherboard class of use, the board can come configured with three, six or nine memory slots.

That's what we are looking at today. but not only will we look at the memory in default configuration, no we'll look at the memory at several frequencies and timings.

Memory timings explained

What are memory timings ?

Let's explain a little what you will run into with memory timings. First off latency. We used the word numerous times already in this article. Latency is the time between when a request is made and the request is answered. I.E, if you are in a restaurant for a meal, the latency would be the time between when you ordered your meal to the time you received it. Therefore, in memory terms, it is the total time required before data can be written to or read from the memory. Thus lower is better.

Say we notice on the packaging is this: 9-9-9-24 (2T) for a memory kit. What do the numbers mean ? Well this refers to CAS-tRCD-tRP-tRAS CMD (respectively) and these values are measured in clock cycles.

CAS Latency
Undoubtedly, one of the most essential timings is that of the CAS Latency and is also the one most people can actually understand. Since data is often accessed sequentially (same row), the CPU only needs to select the next column in the row to get the next piece of data. In other words, CAS Latency is the delay between the CAS signal and the availability of valid data on the data pins (DQ). Therefore, the latency between column accesses (CAS), plays an important role in the performance of the memory. The lower the latency, the better the performance. However, the memory modules must be capable of supporting low latency settings.

tRCD
There is a delay from when a row is activated to when the cell (or column) is activated via the CAS signal and data can be written to or read from a memory cell. This delay is called tRCD. When memory is accessed sequentially, the row is already active and tRCD will not have much impact. However, if memory is not accessed in a linear fashion, the current active row must be deactivated and then a new row selected/activated. It is this example where low tRCD's can improve performance. However, like any other memory timing, putting this too low for the module can result in instability.

tRP
tRP is the time required to terminate one one Row access and begin the next row access. Another way to look at this it that tRP is the delay required between deactivating the current row and selecting the next row. Therefore, in conjunction with tRCD, the time required (or clock cycles required) to switch banks (or rows) and select the next cell for either reading, writing or refreshing is a combination of tRP and tRCD.

tRAS
Memory architecture is like a spreadsheet with row upon row and column upon column with each row being 1 bank. In order for the CPU to access memory, it must first determine which Row or Bank in the memory that is to be accessed and activate that row via the RAS signal. Once activated, the row can be accessed over and over until the data is exhausted. This is why tRAS has little effect on overall system performance but could impact system stability if set incorrectly.

Command Rate
The Command Rate is the time needed between the chip select signal and the when commands can be issued to the RAM module IC. Typically, these are either 1 clock or 2.

Memory testing is a process of trial and error, find and seek the maximum. This is pretty much a sucker for your free time.

Traditional system: If you are going to overclock then increase the FSB, change the memory timings, but most of all alter memory dividers until your system won't boot. If you are not comfortable with such a thing, hey this isn't your game then. I recommend you to lower the processor's multiplier and then slightly increase the FSB with high memory timings and take it from there timings wise. For a Core i7 system: change memory multipliers/dividers in the BIOS or overclock QPI frequency and memory voltage.

6 GB ? You'll need a 64-bit operating system, a 32-bit restriction

Windows 98, who didn't use that OS? What amount of memory did your PC have? Right, likely 128 MB. We now test a system that has 48 times more memory.

Over the years we progressed and noticed that applications have gotten more and more memory intensive. With Windows XP we moved towards 512 MB as standard to prevent the OS from swapping to the HD, and as explained on the previous page with the latest games we see that the certain games really like 1 GB. All this has happened over just a couple of years my friends.

Then Microsoft launched Windows Vista, the biggest memory hog in the world. 1 GB is just be the average recommended specification. They actually recommend 2 GB. And then there's 64-bit platforms supporting more than 4 GB memory. With memory prices coming down you might even consider taking it a step further.

I'm on a 32-bit Operating system. I see 3 GB, where's my 6 Gigabytes of RAM?

Can you use 4, 6 or more GB of memory ? Yes and no. As far as 32-bit operating systems are concerned, the world ends at 4,096 megabytes. That's it. As an example I'll use a 4GB kit here. Say you get 4GB, it will run just fine, yet with for example Windows Vista 32-bit your memory size will be limited and you'll only have 3.2 GB out of the 4 GB available to you. This isn't a Windows problem-- it's an x86 hardware problem.

To address 4GB of memory you need 32 bits of address bus. There however is a problem - actually a similar problem that IBM faced when designing the original PC. You tend to want to have more than just memory in a computer - you need things like graphics cards and hard disks to be accessible to the computer in order for it to be able to use them. Microsoft call this MMIO (Memory-Mapped I/O).

For example, if you have a video card that has 256 MB of onboard memory, that memory must be mapped within the first 4 GB of address space. If 4 GB of system memory is already installed, part of that address space must be reserved by the graphics memory mapping. Graphics memory mapping overwrites a part of the system memory. These conditions reduce the total amount of system memory that is available to the operating system.

So just as the original PC had to carve up the 8086's 1MB addressing range into memory (640K) and 'other' (384K), the same problem exists today if you want to fit memory and devices into a 32-bit address range: not all of the available 4GB of address space can be given over to memory.

For a long time this wasn't a problem, because there was a whole 4GB of address space, so devices typically lurk up in the top 1GB of physical address space, leaving the bottom 3GB for memory. And 3GB should be enough for anyone, right?

So what actually happens if you go out and buy 4GB of memory for your PC? Well, it's just like the DOS days - there's a hole in your memory map for the IO. (Now it's only 25% of the total address space, but it's still a big hole.)

So the bottom 3GB of your memory will be available, but there's a discrepancy with that last GB. If you want it all, go with a 64-bit OS. In 64-bit Windows, the limit is gone.

Anyway, let's have a peek at the modules and throw them at a test.

Corsair Dominator 6GB DDR3, 1866MHz, DHX

So the modules we are testing today are one of Corsairs triple channel memory DIMM kits.

Should you be interested in this memory kit, here's the part number: TR3X6G1866C9DF. Right here we have the 1866 MHz specced memory. A rather nice threesome. This kit has it's SPD programmed at latencies of 9-9-9-24 at a 2T command rate / 1.65 Volts.

• 6144 Megabytes of DDR3 memory
• 3x 2GB modules
• 100% tested at 1866MHz in Gigabyte EX58-UD5 motherboards
• Lifetime warranty
• DHX technology provides maximum cooling
• Each three module set is tested at 1866MHz
• Packaged together immediately following system test
• Tested together at 1866MHz, Vdimm = 1.65V, at latency settings of 9-9-9-24 on X58-based motherboards.
• SPD programmed at: XMP 9-9-9-24 values at 1866MHz JEDEC standard 9-9-9-24 values at 1333MHz.

By the way, very simple stuff but details of the modules and timings can be read from a small sticker. You can spot the SKU number and generic info on there. Also info like latencies are displayed. It's good to see Voltages being reported on there as well. A lot of memory producers lack this info, yet it is so important.

What's quite interesting .. Next to Jedec SPD timings and XMP EPP entries, just play around with the memory a little. There's plenty of headroom to go little crazy. For example, once we fired up 1866 MHz / 1.65V manually in the BIOS, I was just curious to try it out at CAS8, which just was 100% stable. So chances are really good that you can select better latencies straight out of the box without forfeiting on stability whatsoever.

Should for whatever your system fail, rest assured that JEDEC timings are in there (default) as well, which boils down to conservative standard 9-9-9-24 values at 1333MHz.

The kit obviously entails 3x two Gigabyte memory DIMMS. Each module is hand tested and comes with a lifetime warranty. Also notice that this kit came with an airflow fan which you can mount easily over the three modules. Let's have a look at that.

Included in the kit is the Corsair Dominator Airflow fan, labeled IHX (Integrated Heat Xchanger). This is the new model, with two silent fans. The airflow fan unit has two tachometer-controlled fans to apply airflow to the memory subsystem. The usage of fans over your memory I understand is a little controversial, but then again it's moving away residual heat from the heat spreader .. and that's its better than nothing. The old design had three fans, this updated two which are bigger, and thus make less noise.