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ChuangTzu
starvingphysicist



Registered: 09/04/02
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DDR3: Latency vs. Bandwidth
#14304701 - 04/17/11 04:59 AM (12 years, 9 months ago) |
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I'm trying to buy some RAM to upgrade my thinkpad's brains and I can't figure out any criteria for selecting between these two options:
2x4GB DDR3 PC3-8500 CL=7
and
2x4GB DDR3 PC3-10600 CL=9
All else is equal, including price. I know it probably doesn't make much difference, but I need to decide, and I'd rather base that decision on something other than the outcome of a coin flip.
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koraks
Registered: 06/02/03
Posts: 26,670
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Re: DDR3: Latency vs. Bandwidth [Re: ChuangTzu]
#14304733 - 04/17/11 05:22 AM (12 years, 9 months ago) |
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Depends on your mainboard+cpu configuration, and since you include 8500 in the search, I suspect that your configration isn't going to support a higher bandwidth than that anyway, so there's no advantage in going for the 10600 option. Also, note that CL9 @ 10600 is about the same latency as CL7 @ 8500 (a bit over 13ns), so while the latency numbers differ, the real life difference is negligible. http://en.wikipedia.org/wiki/DDR3_SDRAM
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ChuangTzu
starvingphysicist



Registered: 09/04/02
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Re: DDR3: Latency vs. Bandwidth [Re: koraks]
#14304782 - 04/17/11 05:54 AM (12 years, 9 months ago) |
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Both are supported by my system. I wasn't sure how latencies were being reported since units aren't given. I'd seen some numbers in the past given in units of time and some given in units of timing cycles. It's been so long since I've looked into buying RAM that I expected to pay as much for a single 2GB DIMM as these pairs of 4GB modules are selling for... 
I guess that makes it an easy choice then...
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HeavyToilet
The Heaviest OfThem All


Registered: 08/06/03
Posts: 9,458
Loc: British Columbia
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Re: DDR3: Latency vs. Bandwidth [Re: ChuangTzu]
#14306225 - 04/17/11 12:58 PM (12 years, 9 months ago) |
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I could be wrong, but from what I've been told (by people on a computer forum who know way more than I :P) the clock speed is always more important than the timing for performance.
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koraks
Registered: 06/02/03
Posts: 26,670
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Re: DDR3: Latency vs. Bandwidth [Re: HeavyToilet]
#14310210 - 04/18/11 02:04 AM (12 years, 9 months ago) |
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Quote:
ChuangTzu said: Both are supported by my system.
Uhm, in theory, yes, but in practice, the actual speed is determined by the combination of CPU and chipset. What mainboard do you have and what CPU?
Quote:
HeavyToilet said: I could be wrong, but from what I've been told (by people on a computer forum who know way more than I :P) the clock speed is always more important than the timing for performance.
Clockspeed generally has more influence on overall performance, yes.
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ChuangTzu
starvingphysicist



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Re: DDR3: Latency vs. Bandwidth [Re: koraks]
#14310418 - 04/18/11 03:54 AM (12 years, 9 months ago) |
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Quote:
koraks said:
Quote:
ChuangTzu said: Both are supported by my system.
Uhm, in theory, yes, but in practice, the actual speed is determined by the combination of CPU and chipset. What mainboard do you have and what CPU?
It's a Lenovo T410 with i5 520M.
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sandi
omg


Registered: 04/11/11
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Re: DDR3: Latency vs. Bandwidth [Re: ChuangTzu]
#14310435 - 04/18/11 04:13 AM (12 years, 9 months ago) |
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Go for the lower clock speed. No brainer
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koraks
Registered: 06/02/03
Posts: 26,670
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Re: DDR3: Latency vs. Bandwidth [Re: ChuangTzu]
#14310449 - 04/18/11 04:22 AM (12 years, 9 months ago) |
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Then there's no advantage in installing PC3-10600, as it will be limited to PC3-8500 anyway. And I'm not sure if the PC3-10600 with their specced CL9 can be run at CL7 at the slower PC-8500 speed, so I'd opt for the PC3-8500 modules. If you're not worried about the latency, then you might as well buy the PC3-10600 and see if you can get it to run at PC3-8500 @ CL7.
Or just buy any of the two, install it and don't worry about it. There won't be any noticeable differences in any case.
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Seuss
Error: divide byzero



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Re: DDR3: Latency vs. Bandwidth [Re: koraks]
#14310513 - 04/18/11 05:35 AM (12 years, 9 months ago) |
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> There won't be any noticeable differences in any case.
^^^ agree
-------------------- Just another spore in the wind.
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ChuangTzu
starvingphysicist



Registered: 09/04/02
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Re: DDR3: Latency vs. Bandwidth [Re: Seuss]
#14310575 - 04/18/11 06:26 AM (12 years, 9 months ago) |
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Quote:
Seuss said: > There won't be any noticeable differences in any case.
^^^ agree
I already knew that, but I had to decide some how.
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ChuangTzu
starvingphysicist



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Re: DDR3: Latency vs. Bandwidth [Re: koraks]
#14310577 - 04/18/11 06:27 AM (12 years, 9 months ago) |
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Quote:
koraks said: Then there's no advantage in installing PC3-10600, as it will be limited to PC3-8500 anyway.
What's the determining factor in this case?
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koraks
Registered: 06/02/03
Posts: 26,670
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Re: DDR3: Latency vs. Bandwidth [Re: ChuangTzu]
#14310636 - 04/18/11 06:59 AM (12 years, 9 months ago) |
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Your CPU. It has a 133MHz memory clock and therefore 'only' supports PC3-8500. PC3-10600 requires a 166MHz memory clock.
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ChuangTzu
starvingphysicist



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Re: DDR3: Latency vs. Bandwidth [Re: koraks]
#14310688 - 04/18/11 07:22 AM (12 years, 9 months ago) |
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I see. But if I later popped in a pin-compatible i7, I'd have a faster memory clock, right?
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koraks
Registered: 06/02/03
Posts: 26,670
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Re: DDR3: Latency vs. Bandwidth [Re: ChuangTzu]
#14310817 - 04/18/11 08:08 AM (12 years, 9 months ago) |
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Yes, you could upgrade to a Clarksfied i7, and the newer Sandy Bridge models probably support a 166MHz memory clock as well.
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Maverick
Lover of Earwigs!




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Re: DDR3: Latency vs. Bandwidth [Re: koraks]
#14317052 - 04/19/11 12:15 PM (12 years, 9 months ago) |
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Quote:
koraks said: Your CPU. It has a 133MHz memory clock and therefore 'only' supports PC3-8500. PC3-10600 requires a 166MHz memory clock.
This. I guess you could try overclocking your memory clock but usually you hit instabilities, and it's probably easier to just upgrade to the proper CPU to eliminate that bottleneck. Overclocking seems to be more stable done via multipliers over the memory bus.
Quote:
ChuangTzu said: I see. But if I later popped in a pin-compatible i7, I'd have a faster memory clock, right?
This depends on the motherboard. If your motherboard supports a faster memory clock as well then you're fine. I've been limited by the motherboard before, and had to run the RAM and CPU at a lower than average clock.
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Shroomism
Space Travellin



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Posts: 66,015
Loc: 9th Dimension
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Re: DDR3: Latency vs. Bandwidth [Re: ChuangTzu]
#14317138 - 04/19/11 12:29 PM (12 years, 9 months ago) |
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Yep totally dependent on the CPU/motherboard, The memory is probably going to run at 1066MHz since that is the native memory controller frequency on the i5 520m. To achieve a higher frequency on the memory would probably require overclocking the CPU. And chances are that Lenovo has any CPU OCing options completely locked down or non-existent in the BIOS, most laptops BIOS are locked down. Like Koraks said any of the clarksfields or sandy bridge i7s should support 1333mhz, the clarksfields would work in that socket if you wanted to upgrade the CPU.
In short, both sticks of RAM will work in your system. But they are probably going to want to run at 1066. Lower latencies/timings = faster. Higher clock speeds/frequency = faster. But in your case you probably wont notice any difference anyway. Cause chances are you can't OC anything to begin with.
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zgbzgb1
Stranger
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Re: DDR3: Latency vs. Bandwidth [Re: Shroomism]
#14317151 - 04/19/11 12:32 PM (12 years, 9 months ago) |
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bandwidth > all
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Shroomism
Space Travellin



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Loc: 9th Dimension
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Re: DDR3: Latency vs. Bandwidth [Re: zgbzgb1]
#14317207 - 04/19/11 12:43 PM (12 years, 9 months ago) |
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Not when your memory doesn't run at the advertised bandwidth because it's bottlenecked by the CPU. It's like when I have people that buy memory advertised at 2000mhz and put it in their i7 950 at stock clocks and call me to say the board is broken cause it's only running at 1066, nope working as intended. You have to tweak to achieve those numbers. And if you're OCing you need to do aftermarket cooling. Not really viable on a laptop.
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