How to match RAM speed (MHz) to suit CPU & Motherboard?

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htk421

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Friends, (Similar questions have been answered, but I have other questions...)

I'm building a PC, and need some advice on how to choose RAM of the correct 'speed'.
(Assume Ive already covered the basics like DDR4 / number of pins etc).

I can buy DDR4 RAM up to 4000+MHz, but my CPU (i9-7900x) says it requires DDR4-2666

Q1. Does this mean I have to explicitly use 2666MHz ram and no higher ?
(eg.) if I bought 4000MHz ram I would be wasting my money because it would only run at 2666 unless I overclock ?

Q2. Do I need to consider what memory speed the MOBO can support ? is this part of the equation too?



would appreciate your advice
Toby
 
Solution
imsqam
Q1: No, you can use higher speeds of RAM. This is one of the aspects of overclocking, a process of speeding up the computer much like taking a plain street car and souping it up with aftermarket parts. Here is a link about overclocking the 7900x.
https://www.techspot.com/review/1437-overclocking-core-i9/

If you have no intention of overclocking then it will likely be a waste of money to go beyond 2666. But watch the deals, sometimes 3200 is cheaper than 2666. Note the Team Night Hawk RGB 2x8GB kit in this link
https://pcpartpicker.com/products/memory/#s=402666,403200&sort=price&Z=16384002

Q2: You absolutely have to consider the mobo, that is the component that determines which speeds of RAM can be used. Here's an example...
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PC Tailor

PC Tailor

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You can use RAM speeds up to what your motherboard can support. So in essence, your second question answers your first question. The i9-7900x is not limited to 2666. You will just need to overclock to reach the higher timings.

First find what the motherboard support for RAM speed is, then check that whichever RAM modules you want to buy are on the motherboards support list.

If your board supports 4000 - and runs at 2666 natively, then if you put 4000 RAM with the i9-7900x together, it will run at 2666 initially - until you overclock it. Then you can get to your 4000.
 
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imsqam

imsqam

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Q1: No, you can use higher speeds of RAM. This is one of the aspects of overclocking, a process of speeding up the computer much like taking a plain street car and souping it up with aftermarket parts. Here is a link about overclocking the 7900x.
https://www.techspot.com/review/1437-overclocking-core-i9/

If you have no intention of overclocking then it will likely be a waste of money to go beyond 2666. But watch the deals, sometimes 3200 is cheaper than 2666. Note the Team Night Hawk RGB 2x8GB kit in this link
https://pcpartpicker.com/products/memory/#s=402666,403200&sort=price&Z=16384002

Q2: You absolutely have to consider the mobo, that is the component that determines which speeds of RAM can be used. Here's an example specifications for a mobo which supports DDR4-2133 / 2400 / 2666 / 3600 / 4000. You can actually use other speeds but you would have to manually go into the BIOS to set the parameters.
https://pcpartpicker.com/product/vDYWGX/asus-prime-x299-deluxe-atx-lga2066-motherboard-prime-x299-deluxe

Be mindful of cooling with this CPU, it runs extremely hot, you need a superior CPU cooler.
http://www.tomshardware.com/reviews/intel-core-i9-7900x-skylake-x,5092-11.html
 
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htk421

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Sep 22, 2017
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really appreciate your response. It did answer my question. Thank you
 
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htk421

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Sep 22, 2017
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Great response, much appreciated. Thank you.
 
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