PC hardware--CPU & Motherboard & RAM/RAM Modules (Channel Selection)

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QUESTION: I would like to use 16GB of RAM in my next build. I am a speed freak and cannot seem to find a definitive answer to my question. Without selecting a particular motherboard to benchmark I am hopeful that you can give me a more generalized answer.

To get the best speed and performance from my memory is it better to have a 2x8GB configuration or 4x4GB configuration? Why?

ANSWER: It does really depend on the motherboard because it depends on what CPU you're using.
However, most likely it'll make no noticeable difference for quite awhile.

The reason it depends on the CPU is because some processors quad-channel memory buses, essentially meaning they can access 4 sticks at once. They are, however, very new technology and hideously expensive.

So it's a high likelihood that your machine will be the current standard of a dual-channel memory bus. So it will access the memory slot pairs at once.

Whether one slot in the channel is used, with one 8GB, or both slots used with two 4GB sticks, really makes no difference in this instance.

Money wise, 4 x 4GB would likely actually be cheaper than 2 x 8GB. But, if the board you get can handle more than 16GB, if you get 2 x 8GB now it gives you an easy upgrade option.

What DOES matter when buying memory is that they are all the same, and you replace them in pairs.

Hopefully that helps a bit.

---------- FOLLOW-UP ----------

QUESTION: Thank you, Mike.

Allow me to place all potential cost, and upgrade ability to the side. I'm not asking for a recommendation, or whether my CPU or MOBO can handle this configuration. I can determine those benefits and specifications for myself. The mobo I was eyeing would allow for (up to# 32 GB ram. The specs do say it supports dual channel with no mention of quad channel. And the Haswell Intel CPU may or may not support quad channel. I know where to find that information and I will take it into consideration when making my purchases.

Furthermore, I understand the necessity for having same size/same speed ram modules #They are usually sold in pairs anyway and have been tested together for compatibility with each other). But if I am using 4 modules does that mean the mobo I am interested in only sees 2 channels?  Maybe I don't understand fully how Ram is used by the North Bridge and processor.

If there are 4 available lanes of traffic all capable of the same speed and volume wouldn't it make sense that you get increased performance using 4 lanes as opposed to 2 no matter the size? Sure, 16GB is great. But RAM is really just a temporary holding tank. If you have a football stadium with only one entrance and one exit it will still take significantly longer to move people in an out when compared to the same sized stadium with multiple entrances and exits. Is this a bad analogy?

Your answer contained the statement, "Whether one slot in the channel is used, with one 8GB, or both slots used with two 4GB sticks, really makes no difference in this instance." Is this based on real numbers of specific tests or is this a generally accepted theory? As this is the heart of my question, it is what I really want to know.

In closing, I would like to express gratitude for your help. I realize that any potential gains I might acquire from either configuration would likely be so small as to not be noticeable to the user (me). These gains may only be measurable in a program like Memtest. Either way, it was a question I have sat on for some time. I wish things were simpler and all cpu's and mobo's created equal so I could finally have definitive proof that I am either right or wrong in my assumptions.

Answer
Dual-channel memory, the current standard still works something along the lines of your analogy of the stadium. Running 2 x 8 versus 4 x 4 would be the difference of making the doorways in your stadium larger.

On a motherboard you likely have 4 slots.

Slot 1   Channel 1
     
Slot 2   Channel 2

Slot 3   Channel 1

Slot 4   Channel 2

So, if you put one 8 GB into Slot 1 and one in Slot 2 it's running with 8GB per channel. Running 4 x 4 might be a bit less of a load on the system, technically, but you won't see any noticeable performance improvement.

Another analogy would be use two 100 ton Trucks to hall full loads down a freeway. Both travelling side by side, same speed, you get 200 tons of load to it's destination at the same time.
Running four 50 ton Trucks, doing the same thing, accomplishes the same goal, just with a bit more spread out work load.

You're actually getting pretty heavily into more of a Computer Science level question and my in-depth knowledge is getting pretty well strained so I'm only offering my interpretation of how I believe it works.

PC hardware--CPU & Motherboard & RAM

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Mike Rigsby

Expertise

Areas of expertise: PC Hardware, Peripherals, Barcode Scanners, Printers, and Applications, Networking, Microsoft Applications. I am good at researching issues and have a lot of contacts in the IT industry. So, if I can't directly answer a question I can likely find the answer. Areas I won't be much help in: Apple Computers, Linux, older Networking technologies like Token Ring, or Thick/Thinnet.

Experience

I'm currently a Network Administrator for a contract circuit board manufacturer in Oregon, USA. I've been working on PCs from a hobby standpoint for better than 25 years. I've been doing it professionally for 4+ years.

Publications
http://www.pcauthority.com.au/News/275043,opinion-power-users-are-we-a-dying-breed.aspx

Education/Credentials
A+ Certification, Network + Certification, MCP, MCDST, MCITP

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