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Memory and CPU overclocking

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January 21, 2012 10:41:57 PM

If I want memory to run at stock settings (Specified Frequency and timings) above 1333, for example 1600 or 1866 on both an i5-2400 and bulldozer platform do I have to mess with overclocking the cpu or bus in any way?

I've seen posts where the only settings for memory to be changed are frequency the four primary timings (i.e. 9-9-9-24) and command rate.....


I've also seen multiple posts on forum where people have had to adjust voltage and dram ratio?? Confusing.... I don't plan on overclocking, I just want my memory to run at stock speeds. So If I buy a gskill 1600 kit that runs at 7-7-7-24 I just want it to run at those advertised speeds.

Is it more complicated with AMD AM3+ motherboards. I've read where intel 1155 is easier to setup? Very confused. Thank you.
a c 347 } Memory
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January 21, 2012 11:34:40 PM

Nothing to be confused about, every CPU, MOBO and kits of RAM are different. The (CAS-TRCD-TRP-TRAS-CMD) are all that needs to be adjusted, most of the other timings are calculations from (CAS-TRCD-TRP-TRAS). The Command Rate for most all >DDR3-1333 should be set to 2T and it's part of the Rated 'SPD'/JEDEC/XMP timings.

Sparing the 'long' explanation, if you install e.g. DDR3-1600 into e.g. an i5-2400 by default it will run DDR3-1333, if you have an overclocking Intel Chipset P67/Z68 then you'll need to adjust the BIOS to achieve DDR3-1600 and the Rated CAS Timings per Voltage, but on a H67, H61, etc DDR3-1333 is as fast a frequency as you can go - those chipsets lock-out OC's. To confuse you more, the FX default frequency is DDR3-1866 but the RAM will only run up to the fastest non-XMP 'SPD' (JEDEC) which is often DDR3-1333; XMP is an Intel only 'SPD' encoding on the RAM.

Next, is nomenclature: Frequency in reality is a function of typically even number multipliers of BCLK or FSB depending on the platform and chipsets. Some MOBO's simply use 'DRAM Multipliers' while others like ASUS do the calculations for you in the BIOS as expression of 'DRAM Frequency'. Further, are the Voltages - in general I only recommend using 'DRAM Voltage' and not the QPI/VTT/VCCIO/Etc aka as CPU IMC Voltage. Using wrong values can damage both your RAM and CPU.

Further, when looking at CPU-z keep in mind the actual frequency is 1/2 so DDRn (Double Data Rate revision number) the data is transmitted twice per clock; the top and bottom of the Sine wave. So CPU-z expression of DDR3-1600 will show 'DRAM Frequency = 800MHz'.

Nope, LGA 1155/1366 on up to LGA 2011 is just as 'easy' or to some as 'complex'. Thank's above FSB : DRAM ratio concerns are a thing of the past.

In general, I encourage you to either Google and look for a knowledgeable person/thread or create your own thread in Tom's Memory section.
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January 21, 2012 11:35:25 PM

Intel has what is called Extreme Memory Profile abbreviated XMP. When you go into the BIOS with an XMP board and memory set, you just select Profile 1 and it will run it at the speed it is supposed to run at. If you have an AMD system or memory that does not support XMP, you just go into the BIOS and select 1600Mhz, 7-7-7-24 timings and the specified voltage such as 1.5v or 1.65v for new AMD/Intel systems. It is pretty simple.

Hope this helped! :) 
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January 21, 2012 11:53:27 PM

No, if you simply set as stated above without 'thinking' you are guaranteed to have problems.

Example 1: XMP with (2) Kits, same or not = problems.
One (1) Matched Kit with the correct Voltage per Chipset is fine. Two (2) Matched Kits is a recipe for an unstable system and especially with CAS 7 guaranteed BSOD/Post Failure and/or errors. Using the wrong Voltage RAM; example the Sandy Bridge should only use at Rated 1.50v RAM, so if the XMP sets the DRAM Voltage to 1.65v it's deemed by Intel to be too high and cause damage to the CPU over a period of time.

Example 2: AMD non-FX and "1600Mhz, 7-7-7-24 timings" = problems.
The AMD in particular has the most fragile CPU IMC out there, neither the Phenom II X6 or Phenom II X4 can handle >DDR3-1333 without either increasing the FSB -> 240MHz or CPU-NB Frequency -> 2400MHz or on ASUS AI Overclock Tuner -> DOCP. Otherwise you risk errors, BSOD's, and problems.

Further, as I said every CPU and MOBO is different on how to properly set the RAM per the environment. I WISH I could post a two paragraph answer I cannot.

The 'Plug & Play' Defaults are what to do unless you know exactly what you're doing. I've written more posts on RAM than I care to count from folks assuming and arbitrarily making BIOS 'settings.'
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January 22, 2012 12:07:56 AM

A sticky?? No.

SB i7-3930K default IMC is DDR3-1600. Do you want me to go further?!
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January 22, 2012 1:04:52 AM

jaquith said:
Nothing to be confused about, every CPU, MOBO and kits of RAM are different. The (CAS-TRCD-TRP-TRAS-CMD) are all that needs to be adjusted, most of the other timings are calculations from (CAS-TRCD-TRP-TRAS). The Command Rate for most all >DDR3-1333 should be set to 2T and it's part of the Rated 'SPD'/JEDEC/XMP timings.

Sparing the 'long' explanation, if you install e.g. DDR3-1600 into e.g. an i5-2400 by default it will run DDR3-1333, if you have an overclocking Intel Chipset P67/Z68 then you'll need to adjust the BIOS to achieve DDR3-1600 and the Rated CAS Timings per Voltage, but on a H67, H61, etc DDR3-1333 is as fast a frequency as you can go - those chipsets lock-out OC's. To confuse you more, the FX default frequency is DDR3-1866 but the RAM will only run up to the fastest non-XMP 'SPD' (JEDEC) which is often DDR3-1333; XMP is an Intel only 'SPD' encoding on the RAM.

Next, is nomenclature: Frequency in reality is a function of typically even number multipliers of BCLK or FSB depending on the platform and chipsets. Some MOBO's simply use 'DRAM Multipliers' while others like ASUS do the calculations for you in the BIOS as expression of 'DRAM Frequency'. Further, are the Voltages - in general I only recommend using 'DRAM Voltage' and not the QPI/VTT/VCCIO/Etc aka as CPU IMC Voltage. Using wrong values can damage both your RAM and CPU.

Further, when looking at CPU-z keep in mind the actual frequency is 1/2 so DDRn (Double Data Rate revision number) the data is transmitted twice per clock; the top and bottom of the Sine wave. So CPU-z expression of DDR3-1600 will show 'DRAM Frequency = 800MHz'.

Nope, LGA 1155/1366 on up to LGA 2011 is just as 'easy' or to some as 'complex'. Thank's above FSB : DRAM ratio concerns are a thing of the past.

In general, I encourage you to either Google and look for a knowledgeable person/thread or create your own thread in Tom's Memory section.



Thank you for the quick and very detailed response. One of the other confusing things for me were the BCLK and FSB and you clarified that for me. Correct me if I'm wrong but BCLK, FSB, dram multipliers and frequency are all synonymous with each other. The only voltage value I would be comfortable adjusting would be DRAM voltage. I know Sandys aren't supposed to go North of 1.5v. I have no idea about Bulldozer.

In reference to having to overclock... sounds like the new FX bulldozer processors don't require overclocking to run memory at greater that 1333.

For both platforms (1155 and bulldozer) sounds like in order to run ram at advertised timings I just need to adjust the 4 primary timings, command rate, and DRAM voltage to manufacturer advertised/stock specifications. Is this correct? Thank you.


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January 22, 2012 2:09:34 AM

jaquith said:
No, if you simply set as stated above without 'thinking' you are guaranteed to have problems.

Example 1: XMP with (2) Kits, same or not = problems.
One (1) Matched Kit with the correct Voltage per Chipset is fine. Two (2) Matched Kits is a recipe for an unstable system and especially with CAS 7 guaranteed BSOD/Post Failure and/or errors. Using the wrong Voltage RAM; example the Sandy Bridge should only use at Rated 1.50v RAM, so if the XMP sets the DRAM Voltage to 1.65v it's deemed by Intel to be too high and cause damage to the CPU over a period of time.

Example 2: AMD non-FX and "1600Mhz, 7-7-7-24 timings" = problems.
The AMD in particular has the most fragile CPU IMC out there, neither the Phenom II X6 or Phenom II X4 can handle >DDR3-1333 without either increasing the FSB -> 240MHz or CPU-NB Frequency -> 2400MHz or on ASUS AI Overclock Tuner -> DOCP. Otherwise you risk errors, BSOD's, and problems.

Further, as I said every CPU and MOBO is different on how to properly set the RAM per the environment. I WISH I could post a two paragraph answer I cannot.

The 'Plug & Play' Defaults are what to do unless you know exactly what you're doing. I've written more posts on RAM than I care to count from folks assuming and arbitrarily making BIOS 'settings.'

I have heard that Intel says that 1.65v RAM is the maximum for SB CPUs. 1.5V is recommended, but 1.65v is fine. I am going to go with that because I have heard it from many sources. Also, many people run 1600Mhz RAM on PII CPUs without OCing the FSB. When I said 7-7-7-24 timings was just the example I used because it was the one he used.
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January 22, 2012 1:23:13 PM

wwusa83 said:
Correct me if I'm wrong but BCLK, FSB, dram multipliers and frequency are all synonymous with each other. The only voltage value I would be comfortable adjusting would be DRAM voltage. I know Sandys aren't supposed to go North of 1.5v. I have no idea about Bulldozer.

In reference to having to overclock... sounds like the new FX bulldozer processors don't require overclocking to run memory at greater that 1333.

For both platforms (1155 and bulldozer) sounds like in order to run ram at advertised timings I just need to adjust the 4 primary timings, command rate, and DRAM voltage to manufacturer advertised/stock specifications. Is this correct? Thank you.

BCLK & FSB - Are both system bus frequencies.
DRAM Frequency & Memory Multipliers - Are both expressions of memory speed via a multiplier per BCLK & FSB.

Voltage - is a dependency per spec (design limits) of both the CPU, CPU's IMC, and DIMM (RAM).
- ** Sandy Bridge's limit is in part the DIMM Voltage (1.50v) 'limit' but it's also the VCCIO (1.20v), so anything beyond a DRAM <-> VCCIO (+0.30v~+0.35v) yields instability/errors. Example 1.65v DIMM - 0.35v maximum (VCCIO disparity) = 1.30v VCCIO which is too high for the CPU's IMC.
-- Sandy Bridge (LGA 1155) has a Default IMC of DDR3-1333; 21 GB/s bandwidth. However, has a theoretical limit of >DDR3-2400.
-- Sandy Bridge (LGA 2011) has a Default IMC of DDR3-1600; 21 GB/s bandwidth. However, has a theoretical limit of >DDR3-2400.
- FX series Zambezi (Bulldozer) has a much improved CPU IMC and can handle a 1.60v~1.65v DIMM, but still 1.50v DIMM RAM is recommended.
-- FX series Zambezi (AM3+) has a Default IMC of DDR3-1866; 21 GB/s bandwidth. However, has a theoretical limit of >DDR3-2400.

Regarding RAM OC, don't confuse Default IMC 'SPD' with OC'ing the RAM. The memory frequency's default values are different. In addition, don't confuse memory frequency defaults as performance. The Intel CPU is still superior on both CPU and Memory based benchmarks both synthetic and 'real world'. Oddly, the older AMD Phenom II X4 980 outperforms the AMD FX-8150 8-core in memory intensive program tests.

Regarding the last part, to a degree I agree as long as all of the other conditions above are applied first. Correct, in order to achieve Rated Frequency & CAS Timings in cases where you're exceeding the CPU's IMC Defaults you'll need to OC from the BIOS.

@HostileDonut see ** above.

--- footnotes ---

Frequency vs CAS Chart:


Recommendations:
Sandy Bridge (LGA 1155) ; 2x4GB or 4x4GB DDR3-1600 CAS 8/9 Kit
FX series Zambezi (AM3+) ; 2x4GB or 4x4GB DDR3-1866 CAS 9 Kit

Mix-Matching also includes (2) Identical Kits and the Rated for two 2X4GB (16GB) no longer applies and is often slower, higher CAS, so it's best to purchase a fully matched 4x4GB kit (16GB) if 16GB is desired.

>4GB of RAM requires a 64-bit OS ; see - http://msdn.microsoft.com/en-us/library/windows/desktop...(v=vs.85).aspx#physical_memory_limits_windows_7

Gaming 16GB if running 64-bit Games ; see -> http://www.tomshardware.com/reviews/ram-memory-upgrade,...

RAM is cheap now ;) 
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January 22, 2012 7:25:28 PM

jaquith said:
BCLK & FSB - Are both system bus frequencies.
DRAM Frequency & Memory Multipliers - Are both expressions of memory speed via a multiplier per BCLK & FSB.

Voltage - is a dependency per spec (design limits) of both the CPU, CPU's IMC, and DIMM (RAM).
- ** Sandy Bridge's limit is in part the DIMM Voltage (1.50v) 'limit' but it's also the VCCIO (1.20v), so anything beyond a DRAM <-> VCCIO (+0.30v~+0.35v) yields instability/errors. Example 1.65v DIMM - 0.35v maximum (VCCIO disparity) = 1.30v VCCIO which is too high for the CPU's IMC.
-- Sandy Bridge (LGA 1155) has a Default IMC of DDR3-1333; 21 GB/s bandwidth. However, has a theoretical limit of >DDR3-2400.
-- Sandy Bridge (LGA 2011) has a Default IMC of DDR3-1600; 21 GB/s bandwidth. However, has a theoretical limit of >DDR3-2400.
- FX series Zambezi (Bulldozer) has a much improved CPU IMC and can handle a 1.60v~1.65v DIMM, but still 1.50v DIMM RAM is recommended.
-- FX series Zambezi (AM3+) has a Default IMC of DDR3-1866; 21 GB/s bandwidth. However, has a theoretical limit of >DDR3-2400.

Regarding RAM OC, don't confuse Default IMC 'SPD' with OC'ing the RAM. The memory frequency's default values are different. In addition, don't confuse memory frequency defaults as performance. The Intel CPU is still superior on both CPU and Memory based benchmarks both synthetic and 'real world'. Oddly, the older AMD Phenom II X4 980 outperforms the AMD FX-8150 8-core in memory intensive program tests.

Regarding the last part, to a degree I agree as long as all of the other conditions above are applied first. Correct, in order to achieve Rated Frequency & CAS Timings in cases where you're exceeding the CPU's IMC Defaults you'll need to OC from the BIOS.

@HostileDonut see ** above.

--- footnotes ---

Frequency vs CAS Chart:
http://i1013.photobucket.com/albums/af254/Jaquith/CAS_Frequncy_Chart.png

Recommendations:
Sandy Bridge (LGA 1155) ; 2x4GB or 4x4GB DDR3-1600 CAS 8/9 Kit
FX series Zambezi (AM3+) ; 2x4GB or 4x4GB DDR3-1866 CAS 9 Kit

Mix-Matching also includes (2) Identical Kits and the Rated for two 2X4GB (16GB) no longer applies and is often slower, higher CAS, so it's best to purchase a fully matched 4x4GB kit (16GB) if 16GB is desired.

>4GB of RAM requires a 64-bit OS ; see - http://msdn.microsoft.com/en-us/library/windows/desktop...(v=vs.85).aspx#physical_memory_limits_windows_7

Gaming 16GB if running 64-bit Games ; see -> http://www.tomshardware.com/reviews/ram-memory-upgrade,...

RAM is cheap now ;) 


So to distill this a little bit,

If for example I want to run 1600mhz (advertised/stock settings) ram on my i5-2400 or my Zambezi I do not need to adjust or O.C. the processor at all, I need only ensure primary timings, command and dram voltage are within factory specifications (idealy 1.5v for both platforms).
From what I am gathering the previous generation AMD's did in fact need the CPU overclocked to achieve speeds greater than 1333. Is this correct?
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January 22, 2012 7:55:00 PM

On the Intel SB (LGA 1155) DDR3-1600 will default to DDR3-1333 and the corresponding 667MHz JEDEC encoded CAS Timing.

On the AMD FX DDR3-1600 may or may not default to DDR3-1600 and it depends on the highest non-XMP JEDEC 'SPD' encoded on the RAM. See below.

Correct, as I already mentioned certain families of AMD do default to DDR3-1333 but some even slower. It again entirely depends on the CPU.

JEDEC of 800MHz (non-XMP) is available so the Default on an AMD FX will be DDR3-1600 9-9-9-28 @ 1.28v


JEDEC 685MHz (1370 -> DDR3-1333) is available but no JEDEC 800MHz is available so the Default on an AMD FX will be DDR3-1333 9-9-9-25 @ 1.50v; i.e. not DDR3-1600. Again, XMP is an Intel only 'SPD'.


Also note above the different 'Maximum Bandwidth' this is the maximum rated frequency, typically expressed X2, of the CPU.
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January 23, 2012 3:57:42 PM

jaquith said:
On the Intel SB (LGA 1155) DDR3-1600 will default to DDR3-1333 and the corresponding 667MHz JEDEC encoded CAS Timing.

On the AMD FX DDR3-1600 may or may not default to DDR3-1600 and it depends on the highest non-XMP JEDEC 'SPD' encoded on the RAM. See below.

Correct, as I already mentioned certain families of AMD do default to DDR3-1333 but some even slower. It again entirely depends on the CPU.

JEDEC of 800MHz (non-XMP) is available so the Default on an AMD FX will be DDR3-1600 9-9-9-28 @ 1.28v
http://aphnetworks.com/review/g_skill_sniper_f3_12800cl9d_8gbsr2_2x4gb/cpuz.png

JEDEC 685MHz (1370 -> DDR3-1333) is available but no JEDEC 800MHz is available so the Default on an AMD FX will be DDR3-1333 9-9-9-25 @ 1.50v; i.e. not DDR3-1600. Again, XMP is an Intel only 'SPD'.
http://img688.imageshack.us/img688/9549/memoryspd.jpg

Also note above the different 'Maximum Bandwidth' this is the maximum rated frequency, typically expressed X2, of the CPU.


So to distill this even more:

Sandybridge CPU multiplier is completely separate from memory frequency and speed/timings. So no overclock needed. Does this put extra strain on the memory controller? Out of curiosity what is the upper limit for memory speeds on a non-overclocked or "locked" Sandybridge processor? There doesn't seem to be any defined unofficial limit. In the strictest of terms 1600mhz memory is considered an overclock but only on the memory not the cpu.

On Bulldozer the same holds true? No need to do anything with the CPU as the memory controller is completely separate. In addition Bulldozer supports 1866 natively. So 1866 would not be considered an overclock.

Correct me if I'm wrong on any of this.
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January 23, 2012 5:24:16 PM

First, again unless you have either a P67/Z68 chipset on the Intel LGA 1155 you're stuck with DDR3-1333. My experience is more with the i5 and i7 lines and the 'limit' is as I've said >DDR3-2400 depending on the limits of the MOBO. However, in general without OC'ing the Sandy Bridge I don't recommend >DDR3-1866 and it otherwise does place unnecessary strain on the SB's IMC; disparity is high {CPU Frequency : DRAM Frequency}. The limit is stated, it's 21 GB/s bandwidth.

Peak Transfer Rate = transfer rate of (memory clock rate) × 4 (for bus clock multiplier) × 2 (for data rate) × 64 (number of bits transferred) / 8 (number of bits/byte).

DDR3-1600 = 800MHz * 2 * 64-bit * 1/8 = 12800MB/s = 12.5GB/s

21GB/s = 21504MB/s = XMHz * 2 * 64-bit * 1/8
X = 1344MHz = DDR3-2688 and there are DDR3-2600 Kits in the works.

On both the current Intel (LGA 1155/2011) and AMD AM3+ the Memory Multiplier and CPU Multipliers are separate.
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January 24, 2012 12:03:39 AM

Best answer selected by wwusa83.
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January 24, 2012 12:19:04 AM

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