DDR3 Data Rate and Timings with i5 2500k

[Guest]

I've been shopping for DDR3 and seen that CL9 modules are a lot more popular than CL8 modules of the same data rate and cost. Are people just being stupid or what?

Also, the Intel homepage says that 2500k supports 1066 and 1333 data rate memmory, yet I keep seeing people talking about 1600 and higher for their i5, what's up with that?

 

[jaquith]

Welcome to Tom's Forum!

It depends on what you're try to 'do' with your PC, gaming DDR3 1600 CAS 8/9 with 4GB/stick density is your Sandy Bridge 'sweet spot.' > DDR3 1600 is 'better' for extreme multitasking, but IMO kits DDR3 2133+ begins to create problems of stability and errors - particularly IMC errors. In any case stay with 1.50v DDR3 which is ideally the best for Sandy Bridge and with DDR3 1600.

Nice article -> http://www.bit-tech.net/hardware/memory/2011/01/11/the-best-memory-for-sandy-bridge/1

Further, in the past couple months the costs of 2X4GB, 4GB/stick density, has dropped so dramatically that I currently only recommend 2x4GB kits and obviously they require a 64-bit OS.

Examples -> http://www.newegg.com/Product/Productcompare.aspx?Submit=ENE&N=100007611%20600006069&IsNodeId=1&page=2&bop=And&CompareItemList=147|20-231-445^20-231-445-TS%2C20-233-144^20-233-144-TS%2C20-231-426^20-231-426-TS%2C20-231-428^20-231-428-TS The F3-12800CL8D-8GBXM is my favorite DDR3 1600 2x4GB kit.

note the F3-12800CL9D-8GBXL may only run @ DDR3 1333 in 4x4GB.

 

[Guest]

nice article, but how comes it's even possible to use 1600 when intel says 1066/1333? http://ark.intel.com/products/52210/Intel-Core-i5-2500K-Processor-(6M-Cache-3_30-GHz)

and CL8 is always better than CL9 just as it was back in 2007 when I last built a new PC, right?

 

[Leaps-from-Shadows]

Because with a P67 or Z68 board, the memory controller can be forced to run faster than stock with a simple BIOS setting change.

And yes, CL8 is better than CL9, except for one category that some people consider very important: cost. The actual performance difference, because it is so small (barely noticeable in most applications), isn't worth the extra money for a lot of people.

 

[jaquith]

The Sandy Bridge IMC is exceptionally good and easily exceeds the 1066/1333 MHz 'minimum/default spec.' The SB's Max Memory Bandwidth is 21 (GB/s) ; DDR3 2133 17,067 (MB/s) Peak transfer rate OR 21,504 MB/s IMC vs 17,067 MB/s RAM. The toleration of 'Frequency' is the only issue and with an OC of the CPU ~DDR3 2300 MHz is the 'theoretical limit.

I am very aware of the Intel links.

The i7 9xx has a limit closer to DDR3 2200 MHz and even the last generation with OC easily handles the high Frequencies.

{edit} BTW - If you're 'worried' about 'spec' then don't buy any 'K' CPU, anything > 3.8GHz~4.0GHz 'breaks' the 'spec' vCore limits per Intel!

 

[RetiredChief]

jaquith - outstanding as always.
Another thing I like about 1600 ddr3 is with sandybridge 100 MHz clock, it will run in syschronous mode, With Ix-xxx CPUs if the Bus freq is set to even Hundreds it will also run syschronous (reason I liked the bclk of 200 with my I5-750. However this use to be important 5/10 years abou but not so relavent today.

 

[Guest]

jaquith - outstanding as always.
Another thing I like about 1600 ddr3 is with sandybridge 100 MHz clock, it will run in syschronous mode, With Ix-xxx CPUs if the Bus freq is set to even Hundreds it will also run syschronous (reason I liked the bclk of 400 with my I%-750. However this use to be important 5/10 years abou but not so relavent today.

so you're saying that as long as the memory command rate is in even hundreds it will run synchronous with the 2500k?

 

[RetiredChief]

Unlike previous Intel proc the bclk is left at 100 mHz so yes the memory will be sychronous.
Attempt to explain.
Ex - With bclk of 100: DDR3 1600 requires that the bclk Freq be multiplied by 4, but with DDr3-1333 the multiplier is 3 and 1/3. What this means if you look at the leading edge of pulses to the cpu and the ram, for every rising edge of the memory clock pulse there is also a coresponding leading edge applied to memory - Not so with Assychronous operation. For DDR2 and DDR3 Memory data is controlled by the leading and lagging edge of the clock pulse.

Bare in mind, while I like that, with todays speeds it has very LITLE affect - not even notable on benchmarks. This was more an issue back with DDR and DDR2.

For the DDR and DDR2 systems it was also easier to obtain stability, Non issue with todays systems.

Bottom line, I like, but that's me - but has little to no real effect in Ix-XXX or SB systems.

Had to edit my privious post. I had bclk listed at 400, should have been 200 (the 400 was 200 x 2 = memory freq.)

 

[jaquith]

@awe689 - you're putting terms together. The Command Rate has nothing to do with what you're asking; it's a latency timing,

DDR3 SDRAM {DDR3 = Double Data Rate - revision 3} and {SDRAM = Synchronous Dynamic Random Access Memory}. Since all commercially available 'DDR3 SDRAM' is Synchronous the variables are FSB/Base Clock to its' Memory Multiplier similar to a CPU Multiplier; whether it's odd/even/fractional it's still Synchronous.

SDRAM has a synchronous interface meaning it responds to clock signal.

 

[RetiredChief]

^ Could be wrong but sychronous that you reference is internal. While it can Work as Synchronous externally it is not true synchronous. Basicly it "skips" a beat here and there to force synchronous operation. Would have to see a timing chart comparing memory clocks to CPU clocks.

But as I said - Makes no diff in performance.

 

[jaquith]

See -> http://en.wikipedia.org/wiki/Synchronous_dynamic_random_access_memory

"SDRAM has a synchronous interface, meaning that it waits for a clock signal before responding to control inputs and is therefore synchronized with the computer's system bus."

 

[RetiredChief]

^ that is what I Indicated with "Basicly it "skips" a beat here and there " for effective synchonous mode. That is not True sychronous. True sychronous would be that every clock pulse of the memory (leading edge) lines up on a leading edge of a CPU internal Clock pulse.

 

[Guest]

With command rate I meant the rate that the RAM actually operates at, which in this case would be 800mhz for a transfer rate of 1600. At least that's what wikipedia called it.

 

[RetiredChief]

^ Yes, But as I said - Has almost NO performance effect on todays systems (see jaquith's comments on), so don't sweat it. probably should not have brought it up. I'm more of a "purest", like symmetry.

 

[jaquith]

Using WIKI -> 800 I/O bus clock (MHz) and 1600 Data rate (MT/s)

Regardless, DDR3 1600 as I first posted is the 'ideal' RAM for the Sandy Bridge. See the 8GB Kits i posted above. If you want to OC, the F3-12800CL7D-8GBXH is a good bet.

 

[RetiredChief]

^ Totally concur.
I se DDR3-1600 in both my systems. I use CL7, But CL 8, or 9 is fine, depending on cost diff go with the lowest CL rating.
For Sandybridge recommend the 1.50 V. Intel spec sheet indicate 1.575 as max voltage for RAM with the SB CPU. I am using the 1.60 Volt Ram as I already had, and that is only 0.025 over.