Dual-channel RAM
The amount of RAM (Random Access Memory) in a system is
an important factor in its overall performance. So to is that RAM’s
speed and latency. Whether the RAM is operating in single- or dual-channel
mode is also important. So what is dual-channel?
Dual-channel technology depends on several factors, so in this
TekSpek we’ll explore what those are and how they work together.
The Technology
The RAM in most modern PC systems is either DDR or DDR2.
As you might expect, DDR2 supersedes DDR and the two technologies
are in some ways similar; something we’ve explored in another
TekSpek.
Irrespective of whether the RAM is DDR or DDR2, it connects to
the system’s memory controller by a 64-bit wide bus or channel.
In current Intel-based systems, this memory controller resides on
the ‘northbridge’ of the chipset on the motherboard.
In AMD-based systems, the processor contains the memory controller.
With just one memory channel, it doesn’t matter how much
memory you put on it, there’s still a limit to the rate at
which data can be transferred.
However, what if there were two memory channels? The RAM itself
is still only 64-bits wide and can only interface with one channel,
but there’s now two 64-bit memory channels… a dual channel
configuration. To make use of this feature, two RAM modules will
be required.
Two RAM modules, each with their own channel… dual-channel
RAM. It’s like RAID-0 for memory. Simple! Well, there are
still a few things to consider.
You’ve probably seen ‘dual-channel kits’ of memory
available. These consist of two modules of the same RAM. In many
cases, the system’s memory controller can only operate in
dual-channel mode when both channels have the same RAM in them.
Sometimes you can get away with same-sized modules running at the
same speed, but to play it safe the same modules should be used.
If a motherboard has more than two DIMM slots (say, four) then
where does the RAM go? The motherboard’s manual, or colour
coding, should indicate which slots are used for which channel and
how to install the RAM for a dual-channel configuration. Dual-channel
with four DIMMs is often possible too, but overall operating speeds
can drop as a result.
Just as motherboards have varying support for certain memory modules,
dual-channel support varies too. It’s often useful to check
a motherboard manufacturer’s website to see what compatibility
is like before making a RAM purchase.
So, once the dual-channel configuration is up and running, what
are the benefits? In theory, double the bandwidth that was available
before. Parallel solutions like dual-channel doesn’t always
translate directly to double the performance, however, so the benefits
will vary depending on the circumstances.
The Market
All modern enthusiast motherboards and even mid-range boards
should support dual-channel memory. AMD’s Socket 754 processors
(for their budget CPUs) are not dual-channel capable. Socket 939
processors are.
Dual-channel memory kits are readily available, although buying
two of the same RAM module will often be as good, even though the
modules won’t have been verified as dual-channel capable together.
Dual-channel technology exists for both DDR and DDR2 RAM and there’s
little sign of (and no point in) reverting back to a single-channel
architecture. It’s commonplace now, compared to just three
or so years ago.
The Players
AMD is responsible for dual channel support on the memory
controllers of its CPUs. Chipset manufacturers have a role to play
too, particularly for Intel systems, so that includes ATI, NVIDIA,
SiS and VIA. Then of course, there are the motherboard manufacturers,
of which there are too many to list.
As for the RAM itself, some companies provide special kits, as
we’ve already mentioned. These include Corsair with their
TwinX range, Mushkin, OCZ, Kingston and many more. A lot of the
modules will be derived from the same memory chips, but they may
be rated to run at different speeds, configured or tested differently.
As with any purchase, making the right decision is important if
you want the best performance, so seek the advice of those on hardware
forums if you have any doubts.
