How important is to have matching speed of RAM?

I have a 4GB DDR3 800Mhz recently I installed another 4GB. It turns out it's DDR3 667MHz. Does it really matter I should own both rams 800MHz?

Screenshot

Slot1 shows recent RAM installation. ALSO I don't know if this is 1600MHz (it shows 800x2 and 667x2 for other) or just 800MHz ram.

emrecnl

Posted 2015-05-28T09:49:35.673

Reputation: 394

Well this has been marked as a suplicate while I was typing and apparently I can no longer answer but if you want a pretty complete answer to your question, this is what I had http://markdownshare.com/view/a6658da4-6995-448b-8e87-2818c978cec0

– flungo – 2015-05-28T10:07:48.370

Answers

Usually your computer steps down to the common lowest speed. So if you add DDR3 memory at 667MHz and memory at 800MHz then all of your RAM will run at 667MHz.

This means that:

Memory access will be slower than before,
But you also have more memory.

In most cases more memory trumps qua performance.

Hennes

Posted 2015-05-28T09:49:35.673

Reputation: 60 739

Thanks for the quick reply. This made me wonder another thing. Do you think there will be noticeable performance drop if PC is using 667Mhz instead of 800Mhz. Ps. I play 3d games a lot. – emrecnl – 2015-05-28T09:59:44.220

1No, I don't think the performance impact will be noticeable in games. You could see it in synthetic benchmarks though. Maybe it's 1-2 fps, but nothing that will cause a huge problem. If you'd have DDR3-2133 and 1300, okay, that could make a difference. But 1600 and 1300... – Marin Althuis – 2015-05-28T10:02:22.527

Most of the case: no. If you run a program which uses a dataset which is both large enough that it does not fit in the CPU caches, but small enough that it does not need the extra memory then things might slow down. But that is a rather specific case. (And a momory benchmark is a very specific case). But on average: No. RAM speed always was slow and x86 already works around that. As a result you will probably only gain performance. – Hennes – 2015-05-28T10:03:56.097

All RAMs will run at the speed of the slowest. So regarding performance it is better to have the same speed on all dimms. The improvement is not that big though. More RAM will have a greater impact.

For DDR3 1333 and 1600 Mhz are typical speeds. The x2 comes from the Double Data Rate. Wikipedia says:

"Describing the bandwidth of a double-pumped bus can be confusing. Each clock edge is referred to as a beat, with two beats (one upbeat and one downbeat) per cycle. Technically, the hertz is a unit of cycles per second, but many people refer to the number of transfers per second. Careful usage generally talks about "500 MHz, double data rate" or "1000 MT/s", but many refer casually to a "1000 MHz bus," even though no signal cycles faster than 500 MHz."

from http://en.wikipedia.org/wiki/Double_data_rate

Marin Althuis

Posted 2015-05-28T09:49:35.673

Reputation: 309