Question: Just what exactly is dual channel memory?

Read our answer below:

This indeed confuses many people and what's even more perplexing is that some memory manufacturers sometimes even use the term on their packaging. Luck has it that we'll beat this confusion but before we do a brief explanation is called for. You see, there really is no such thing as dual channel memory. What exists however is memory (also referred to as RAM or Random Access Memory), in this case laptop memory that comes in the form of SODIMM's (the type of package) that can (as an option) be used in a dual channel configuration. This means that each SODIMM can either function on its own or alongside a second identical SODIMM to deliver the performance benefit that stems from dual channel operation. Since most laptops today ship with two SODIMM slots, likewise two DDR2 or DDR3 SODIMM's can be installed and run in dual channel mode. For those laptops that feature four SODIMM slots, you can still run its system memory (RAM) in a dual channel configuration so long as you install two identical SODIMM pairs. Why do select memory manufacturers sometimes write 'dual channel memory' on their packaging? The logical answer to this is that they want to afirm to each potential buyer that this sales package consists of two identical SODIMM's, which depending on the buyer's discretion can be installed as a pair in one laptop or singly in two different laptops. Obviously where possible the sensible thing is to install both in the same laptop and reap the extra memory bandwidth this yields.

So with that settled just what does memory installed in a dual channel memory configuration achieve? For this let us picture how the memory controller handles the installed RAM. In DDR2 and DDR3 laptops each SODIMM slot is treated as a channel. Consequently, for laptops with two SODIMM slots there are two (hence dual) channels. For high-end laptops with four SODIMM slots there are four channels albeit due to current memory controllers featured in laptops not supporting tri channel or quad channel memory access, each pair or SODIMM slots can only be used in either a single or dual channel memory configuration. Each of these channels is accessed separately by the memory controller. Should the DDR2 or DDR3 system RAM be installed in a dual channel configuration (remember, this means two identical SODIMM's) then each channel (hence SODIMM) will be accessed concurrently. The net result is a boost in memory bandwidth, otherwise defined as the number of bytes that flow to and from the memory modules. This boost can translate into faster application performance depending on its reliance on frequent memory access.

And the bottom line? It's quite simple really, if you want to get the most out of your laptop's DDR2 or DDR3 memory sub-system then go for an identical pair(s) of SODIMM's. If you laptop has two SODIMM slots then install them in both (usually denoted as A0 and B0 or A1 and B1), if your laptop has four SODIMM slots, install each SODIMM pair to occupy them all (usually denoted as A0 and B0 or A1 and B1 for the first two SODIMM slots and A1 and B1 or A2 and B2 for remaining slots 3 and 4).

Want to learn more about laptop memory modules? Take a look at part 3 of the Laptop Memory Upgrades Guide.

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Read the Laptop Memory Upgrades Guide to learn about all the aspects you should know when buying laptop memory...

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PC2-6400 800MHz DDR2 200-pin SODIMM Dual Channel kits

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