What is more important - CL or MHZ?

Flogger23m

[H]F Junkie
Joined
Jun 19, 2009
Messages
11,255
Looking to buy some RAM but I am on a tight budget. Cheapest things I can find in stock at the moment is:

Corsair Value RAM at 1333 MHZ at CL9:

http://www.newegg.com/Product/Product.aspx?Item=20-233-192&SortField=0&SummaryType=0&Pagesize=10&PurchaseMark=&SelectedRating=1&VideoOnlyMark=False&VendorMark=&IsFeedbackTab=true&Keywords=%28keywords%29#scrollFullInfo

Or Patriot 1600 MHZ at CL11 (I can buy it for $10 less):
http://www.newegg.com/Product/Product.aspx?Item=20-220-570&SortField=0&SummaryType=0&Pagesize=10&PurchaseMark=&SelectedRating=1&VideoOnlyMark=False&VendorMark=&IsFeedbackTab=true&Keywords=%28keywords%29#scrollFullInfo

My question is what is more important, having a higher MHZ but a lower CL, or having a higher CL but lower MHZ?
 

cyclone3d

[H]F Junkie
Joined
Aug 16, 2004
Messages
13,800

Flogger23m

[H]F Junkie
Joined
Jun 19, 2009
Messages
11,255
Both of those are horribly priced.

In any case, I would go for 1600 CL11 given the same voltages.

Here are some more choices, All 1.5v 1600 CL9, one is even $55 with the $10 off promo code.

Team Vulcan $55 with $10 promo code:
http://www.newegg.com/Product/Product.aspx?Item=N82E16820313345

Wintec $64
http://www.newegg.com/Product/Product.aspx?Item=N82E16820161594

Apotop $64
http://www.newegg.com/Product/Product.aspx?Item=9SIA1YV0SC8873

Never heard of any of those brands save for Wintec. Are they reputable and good quality? I prefer quality and stability over speed.
 

Nenu

[H]ardened
Joined
Apr 28, 2007
Messages
19,532
CL ratings are not directly comparable unless using the same MHz memory.
For example, CL8 is has lower latency than CL11 when comparing 1600MHz modules.
But 1600MHz CL8 has higher latency than 2400MHz CL11.

Reason
CL is the number of clock ticks before an operation occurs.
As the frequency increases, the time taken for those clock ticks to occur reduces.
Higher CL latency ram at higher frequency 'can' have lower real world latency.
If 50% more clock ticks occur in the same time (1600MHz to 2400MHz ram), a longer CL latency of 37.5% (going from CL8 to CL11) gives a latency reduction.
 

cyclone3d

[H]F Junkie
Joined
Aug 16, 2004
Messages
13,800
Thanks for the chart. So CL9 at 1333 is a tad bit faster than CL11 1600, though they are very close.

I can double check when I get home. I am thinking that throughput may be slightly higher at 1600 CL11 depending on the setup.

It also depends on what the BIOS sets the rest of the timings to.

If it tightens up the rest of the timings at 1333 compared to 1600, then yeah, it may be a tiny bit faster.
 

Nenu

[H]ardened
Joined
Apr 28, 2007
Messages
19,532
Yep. That is only the effect of the CAS rating.
The benefit from the extra bandwidth at 1600MHz can help also.
The real world difference for either isnt that large (for most uses), but the 20% increase in MHz outweighs the very minor latency loss imo.
 

DejaWiz

Fully [H]
Joined
Apr 15, 2005
Messages
20,745
^ that Team memory way up there is a good brand. I built an i3-2100 system a few years back and bought 2x4GB DDR3-1600 Team modules. Absolutely flawless. If I didn't score a deal on the low profile memory that I am running now, I was going to pull the trigger on some Team Vulcan red colored modules that were the same speed and latency as my current LP modules. I ended up spending $10 more for the Crucial set, but getting LP (and LV, to boot) was worth it to me. I would have been happy with either, I'm sure.
 

Flogger23m

[H]F Junkie
Joined
Jun 19, 2009
Messages
11,255
Did some more browsing, and it looks like Team Vulcan is a rather small brand but does seem to be highly regarded. With the promo it was just under $60 shipped, making it the cheapest of them all. The Corsair/Patriot was $65+ $5.85 tax; $10 higher. So I went ahead and bought the Team RAM from newegg. Been a while since I ordered from them, lets hope eggsaver shipping isn't so long.

Thanks for the help and thanks for the chart. CL9 + 1600 MHz should be good enough for me I hope.

My only concern is do you think these will be sold in the future if I need another kit?
 

Nenu

[H]ardened
Joined
Apr 28, 2007
Messages
19,532
Here have a read. This explains it very nicely.
http://anandtech.com/show/7364/memory-scaling-on-haswell

This is a great article up to the gaming tests.
The results are very well presented and easy to assimilate.
(dont read the graphs literally, the top row is not time in seconds, it is CAS latency - described on page 1 of the article)

But the gaming tests are pointless, all are at 720p so there is no real world scenario for those that give a damn about their gaming experience.
Even the triple card Crossfire tests are at 720p!
I'm blown away by the waste of a good opportunity to get some useful gaming results published.
The % increase in fps will be much lower at 1080p, I fancy this is why they didnt publish them because they wanted to make the article have more clout.
Such a shame.
 

tatm Mrk.RIVE

Limp Gawd
Joined
Sep 2, 2013
Messages
209
low cas with high MHZ (wow I do not know how I did that need to stop using pc at 1am)
 
Last edited:

Nenu

[H]ardened
Joined
Apr 28, 2007
Messages
19,532
heh.
His sig says "I like pc components too much."
Sounds like he does the dirty with them, redefines a dirty write :p
 

KILLER_K

Supreme [H]ardness
Joined
Feb 6, 2008
Messages
4,597
It would be nice to actually be able to get some low timings with high mhz though. Too bad the tight timing days are gone though. I was just sitting there looking at some pc 3200 with timings of 2-3-2 on them.

low cas with high timings

The rest of his post are basically the same. But I guess you have to get to 50 one way or the other though.

heh.
His sig says "I like pc components too much."
Sounds like he does the dirty with them, redefines a dirty write :p
 

tatm Mrk.RIVE

Limp Gawd
Joined
Sep 2, 2013
Messages
209
You have to get to 100 some how***

Marketplace privileges is what I am after! I need me some rare parts!


and no kidding about the companies ignoring cas these days. i was lucky to catch a 2 kits of G. skill 2400 cas 9 (2x4GB kits). still slower than my 2 kits of http://www.newegg.com/Product/Product.aspx?Item=N82E16820231351
or my 4 samsung VVLP sticks I had at 10-12-11-31 2460mhz(my current record holder)

Anyways if you woould be so kind as to give me a second chance

Heres a reply to a question I posed about my rams I posed the equation off the rog boards for comparing ram "(CAS/frequency) x 2000 gives you a number in nanoseconds for comparing speeds.

Say you see a 1600 kit at 7-8-7-20 and a 1866 kit at 9-10-9-28 which is faster?
Well 7/1600 x 2000 = 8.75 nanoseconds; 9/1866 x 2000 = 9.646 so the 1600 kit actually looks quicker.

If these numbers are close or the same choose the higher frequency it will be more efficient."



their reply:
"Here is an example with the math to take this a bit further. I'll use the example that TatnNRKIV started. However, I disagree with his equation. I'm not sure why he is multiplying by 2000. Maybe that would make sense if he was using the single data rate speed, but he is using the double data rate speed in the equation. So let me redifine the equation and explain why it is the way it is.

The timing numbers refer to the number of clock cycles it takes to complete that action. 1600MHz means there are 1600000000 clocks per second (1600Mhz is like saying 1600 Million). So, you take the total number of clocks it takes to complete an action, then divide it by the clocks per second. That leaves you with time in seconds. The math is simple:

(# of clocks)
===============
(# of clocks) / (Second)

When you divide twice as shown above, the second division is the same as multiplying to the numerator (the number on top). So you get:

(# of clocks) X (Second)
===============
(# of clocks)

Both (# of clocks) cancel each other out and you are left with the time in seconds. Remember that this is time in Seconds so it will be very small. And by very small I mean something like 0.000000025 seconds. Which is the same as 25 nano seconds (ns).



Now that we have a proper equation lets do the math to figure out how much data you would need to transfer to in one shot to have the 1866MHz ram actually be faster.

1600MHz has a data rate of 12.8GB/s
1600MHz latency = (7+8+7+20)/1600000000 = 26.25ns

1866MHz has a data rate of 14.9GB/s
1866MHz latency = (9+10+9+28)/1866000000 = 30.0107ns

So, based on the two latencies we have, the 1866MHz ram would need to transfer the data 30.0107 - 26.25 = 3.7607ns faster just to match speeds.

The equation to find out how quickly a set chuck of data is transferred is also very simple:

(Amount of Data)
=========== = Total time to transfer the data
(Transfer Speed)

Using some algebra magic you can rearrange the equation to look like this:

(Amount of Data) = (Total time to transfer the data) X (Transfer Speed)


We also need to remember that the 1600 ram has already been transferring data for 7ns. So using the equation above we know that it has already transferred

12.8GB/s x 3.7607ns = 48.14 Bytes (note that it's Bytes, NOT GigaBytes).


So now we need to know how long it will take for the 1866 ram to "catch up" in terms of how much data it has transferred. We know that the 1866 ram transfers data at 2.1GB/s (14.9GB/s - 12.8GB/s) FASTER than the 1600 ram. So if we use the above equation again we get:

(48.14 Bytes) / (2.1GB/s) = 22.92ns.

This means it takes 22.92ns of the 1866 ram transferring data before it catches up to how much data the 1600 ram has sent. (Remember, the 1600 ram had a 3.7607ns head start).


Knowing how long the 1866 ram needs to transfer for before it breaks even we can plug that into the "Amount of Data" equation from before:

(Amount of Data) = 22.92ns X 14.9GB/s
(Amount of Data) = 341.56 Bytes

So, unless you transfer at least 341.56 Bytes every time you access a single address in the ram the 1600 ram with lower timings will be faster.

Now the kicker, how much data can be transferred before you have to access another address? I honestly don't know. I emailed Corsair about this and they said I'll need to call the tech department to get an answer which I haven't done yet. But, being an engineer I know that it can be small like 8 Bytes per access or large like 32MB per access or even larger depending on how they designed the architecture.

I know most of you are probably thinking "I transfer way more than 341 Bytes with all my application. My RAM loads at least 1GB when I start any program." Yes, that is true, but ram is set up like a grid and the latencies refer to how long it takes to access sections of that grid. So if there are only 20 Bytes of data in one section of the grid that you need before you go to another section then you need to add those latencies in again to get to the next section and so forth. So even though you may have only clicked one button on your desktop your ram may be jumping all over the place to get the data.

Hopefully I'll get an answer from Corsair soon as to how much data can be accessed at a time (between latencies). Once I get that we will have a very concrete formula and I will put together an Excel sheet where people can plug in their numbers and have excel just tell them which setup would be faster.

Oh, and a second kicker and the second question I asked Corsair. Does ram have a fixed multiplier of 8? If it does, then that means your max ram speed (even if you set it higher) is going to be your base clock (bclk) multiplied by the ram multiplier. The bclk is typically 100MHz. So:

100MHz X 8 X 2(for double data rate) = 1600MHz.

Now you can increase your bclk to get higher data rates. For example if you increased your bclk to 125MHz then you data rate would be:

125MHz x 8 x 2 = 2000MHz.

I could be wrong as I haven't gotten an answer yet. But if I'm right this explains why people don't see that great of performance gains over 1600MHz, but they saw huge gains going from 1333MHz to 1600MHz.

Sorry for the long winded answer, but there was a lot of math that needed to be explained.

Let me know if anything needs clarification."
 
Last edited:
Top