RAM question - Regarding "Dual-Channel Memory Architecture"

[prady16]

Hello Experts!

I was reading through the 15" MacBook Pro Technology Overview pdf file on the detailed specifications page of the same and came across this particular excerpt from that.

"if both slots are loaded with an equal amount of RAM, you can take advantage of the system’s dual-channel memory architecture for an additional performance boost. With a dualchannel memory interface, both banks of SDRAM can be addressed at the same time, enabling MacBook Pro to reach a memory throughput of up to 10.7 GBps."

I am not much of a computer architecture person but i am not totally ignorant to it.

-Can someone please explain in more technical terms as to how exactly does addressing both the RAM chips 'at the same time' can increase the throughput?
-Moreover what exactly do they mean by addressing both the memory banks at the same time? How do they do it?
-Is this the case with PCs as well?
-Is this because of the Intel architecture or because of Apples OS X?

Cheers!

 

[danielbriggs]

Bit of a Wiki for you:


Dual-channel architecture DDR SDRAM describes a motherboard technology that effectively doubles data throughput from RAM to the memory controller. Dual Channel-enabled memory controllers utilize two 64-bit data channels, resulting in a total bandwidth of 128 bits, to move data from RAM to the CPU.

In order to achieve this, the DDR SDRAM memory modules must be installed into matching memory slots, which are usually color coded on the motherboard. Each memory module in each slot should be identical to the one in its matching slot. It's also possible to use similar memory sticks from different manufacturers or different production series as long they are of the same size, specification, the same number of memory chips and internal organization. However, several motherboard manufacturers only support configurations where a "matched pair" of modules are used. For this reason, most memory manufacturers now sell "kits" of matched pair DIMMs.



Dual channel technology was created to address the issue of bottlenecks. Increased processor speed and performance requires other, less prominent components to keep pace.

The most conspicuous of these parts is the memory controller, which regulates data flow between CPU and the system memory (RAM). The memory controller determines the types and speeds of RAM as well as the maximum size of each individual memory module and the overall memory capacity of the system. There are many memory controller designs; prior to 2003, the most common was the single channel configuration. Among its advantages are its low cost and flexibility. Its ability to produce a bottleneck effect arises when it is unable to keep up with the processor, leaving it with nothing to process while the memory controller is struggling to keep up with the data flow. Under the single channel architecture, any CPU with a bus speed that is greater than the memory speed would be liable to fall prey to this bottle-neck effect.

The dual channel configuration alleviates the problem by doubling the amount of available memory bandwidth. Instead of a single memory channel, a second parallel channel is added. With two channels working simultaneously, the bottleneck is reduced. Rather than wait for memory technology to improve, dual channel architecture simply takes the existing RAM technology and improves the method in which it is handled. While the actual implementation differs between Intel and AMD motherboards, the basic theory stands.

 

[mrdice87]

curious...

so, if i buy a mbp with 1gb, could I add another gig from crucial and have it run in dual-channel, or do they have to be exactly the same?

 

[danielbriggs]

so, if i buy a mbp with 1gb, could I add another gig from crucial and have it run in dual-channel, or do they have to be exactly the same?

That should be fine, as long as they are the same spec and capcacity.