Overclocking and ram?

[treyvon]

I'm new to some of the more advanced sections of hardware and computers so bear with me. I saw something earlier this week about overclocking and how ram is significant in your overclocking potential. Is this true? if not what then what is most important in overclocking?

 

[a4mula]

It really depends on what microarchitecture you're overclocking with. On 1155 it makes virtually no difference because of the limited BCLK (base clock) flexibility.

On older systems like 1366 it could play a larger role because many times you relied on a high variance in BCLK to reach stable speeds. BCLK effects not only the cpu frequency but also memory frequency so if you were relying on high BCLKs your memory could very well get in the way.

If you are talking about Sandy Bridge then there's really only three main factors:

Chipset: H61 and H67 do not allow multiplier changes. P67 and Z68 do.

CPU: Only the K series cpus have unlocked multipliers. If you get a non-K cpu then you're pretty much capped at that 5% BCLK bump.

Cooling: Your cpu is only going to be pushed as far as its tjmax allows it. The better you can dissipate heat the more you can push the cpu. This is why stock coolers aren't recommended for overclocking, while extreme cooling like L2N can achieve record breaking overclocks.

Luck: Different processors perform differently even within their own binning. Some are more stable and handle higher voltages better than others. You hear stories about people that can get their Sandy Bridges up over the 5ghz mark. They are very fortunate as very few chips are of this kind of quality.

 

[blazorthon]

The cooler master hyper 212 CPU cooler can get decent overclocks on Sandy bridge k edition CPUs p to around 4.3-4.4 GHz and only costs $20-30. It probably offers the best price/performance for any overclocking cooler because the much more expensive coolers still don't go to much higher than 5GHz, not quite as huge gain from 4.4GHz then going from 3.2/3.3/3.4GHz to 4.4GHz but the better coolers can cost over $60-120.

I use the hyper 212 on my overclocked AMD Phenom II 1090T and right now it's sitting at slightly over 4GHz with 6 cores and can probably go higher if I wanted to, but I added another 92mm fan to it for push/pull improved airflow.

For Sandy Bridge CPUs the memory is of less importance in getting high CPU overclocks because the CPU clock is more independent of the RAM frequency than previous systems. This is because (like the above poster said) Sandy Bridge overclocking is done almost purely with increasing the clock multiplier of the CPU, a change from increasing both the BLCK and the multiplier.

All Sandy bridge CPUs have their BLCK at 100MHz by default. Unlike pretty much all other architectures the Sandy Bridge BLCK effects more components than previous systems BLCK. For Sandy it effects just about everything and some components are not capable of increasing their frequency much, hence why the Sandy BLCK usually can't be increased by more than 5% (if that much) safely.

Other platform's BLCK doesn't control as many sensitive components and thus can be increased significantly, sometimes increased over 50%. For all systems that employ a BLCK, at least the memory and CPU are based off of it. Sandy Bridge is no different in this regard but is different in what else the BLCK controls.

Since memory and CPUs are usually less sensitive to clock increases/decreases the BLCK is more free for change on the other systems such as all of AMD's systems and Intel's Nehalem and previous platforms. Lets say you have an AMD AM3 system with a Phenom II 1090T like mine. Stock settings for the BLCK, CPU, and memory are as follows:

BLCK = 200MHz
CPU = 3200MHz
CPU multiplier = 16 (16 times the 200MHz BLCK equals 3200)
RAM = 667MHz (667MHz times 2 for the double data rate that all current system RAM employs means 1333MHz)
RAM multiplier = 3.33

The BLCK times the CPU multiplier gives the CPU frequency and the BLCK times the memory multiplier gives the memory frequency. This is even true for Sandy Bridge. Sandy Bridge overclocking is just changing the CPU multiplier from its default to a higher number. For a Sandy Bridge system with the i5-2500k CPU, here is the math:

BLCK = 100MHz
CPU = 3300MHz
CPU multiplier = 33
RAM = 667MHz (also double this to get the as-marketed frequency or 1333MHz)
RAM multiplier = 6.67

Increasing the BLCK without changing the CPU or RAM multipliers for Sandy Bridge would change the math to this:

BLCK = 105
CPU = 3465MHz
CPU multiplier = 33
RAM = 700.35MHz
RAM multiplier = 6.67

Not a significant over clock this way. Now for 25% BLCK overclocking of the AMD Phenom II system:

BLCK = 250MHz
CPU = 4000MHz
CPU multiplier = 16
RAM = 833.75MHz
RAM multiplier = 3.33

That is a significant overclock by only changing the BLCK. The RAM went from 1333MHz to 1666MHz and the CPU from 3200MHz to 4000MHz. To get such a significant overclock on the Sandy Bridge i5 system you would need to increase the multiplier, lets also get about 4GHz here. I'll leave the 5% BLCK overclock in here too.

BLCK = 105MHz
CPU = 3990MHz
CPU multiplier = 38
RAM = 700.35MHz
RAM multiplier = 6.67

And now without the minor BLCK overclock:

BLCK = 100MHz
CPU = 4000MHz
CPU multiplier = 40
RAM = 667MHz
RAM multiplier = 6.67

Notice how with the Sandy Bridge system the RAM is untouched by CPU overclocking that doesn't involve the BLCK and even with BLCK overclocking the RAM isn't effected much, just an increase from 667MHz to about 700MHz. Besides Sandy Bridge, many CPUs often can't get the highest overclock possible for them by multiplier overclocking alone because there is a diminishing returns sort of problem with high multipliers on many CPUs. Also, BLCK overclocking improves the memory performance even if you lower the RAM multiplier to keep the memory close to it's default speed so an increased BLCK and decreased CPU multiplier and RAM multiplier are often more desirable. The higher BLCK also improves the performance of other components tied to it but not the RAM multiplier or CPU multiplier such as some CPU caches.

Also important, currently only three Sandy Bridge CPUs support multiplier overclocking: the i5-2500K, the i7-2600K, and the i7-2700K. The i7-2700K is identical to the i7-2600K logically but it is slightly higher binned (look at the last paragraph of the above posters comment, titled "luck") so it will overclock slightly better than the i7-2600K.

This is a slightly simplified scheme but it shows the point just as well as the complete picture would. For example, there are two other important frequencies based off of the AMD system's BLCK, the Northbridge frequency and the Hyper Transport frequency. At stock they both have a multiplier of 10 to get 2000MHz when the BLCK is unchanged. The Northbridge frequency indirectly effects the RAM and controls the frequency of the L3 CPU cache. It basically serves as a replacement for the old FSB. If I remember correctly the Hyper-Transport bus connects the CPU to the chipset.

The Northbridge frequency can slightly improve performance but I lowered both it's and the Hyper-Transport multipliers to 8 to keep them at their default frequencies for safety.

Changing a multiplier does not directly effect any component besides the one your changing.

Excluding the Northbridge frequency and the Hyper-Transport frequency, the math for the AMD system would be the same as the math for Intel's older Nehalem CPUs (LGA 1156 and LGA 1366) and Intel's Core 2 CPUs (LGA 775 and LGA 771). Including the Hyper Transport and Northbridge frequency the AMD Phenom II math should also be the same as AMD's current Athlon IIs (AM3), AMD's newer FX CPUs (AM3+), AMD's older Athlon/Phenom CPUs (AM2/AM2+), and is similar to the math of AMD's Llano APUs (FM1). It is also similar/identical to many older CPU micro-architectures than the Athlon/Phenom and Core 2 lineups but I won't go listing every CPU series ever made.

Note that the captions that have LGA or AM after a CPU series name are the names of the socket that the CPUs were designed for. AMD's CPUs often can be used in three different sockets, the previous, current, and next socket but Intel locks each CPU into a single socket. LGA means Land Grid Array and refers to the fact that CPU pins are located on the motherboard instead of the CPU because this makes increased pin counts more easy to make and decreases the chance of damaging a pin, among a few other reasons. AMD sockets are PGA meaning Pin Grid Array because the pins are on the CPU instead of the motherboard. AMD didn't make the switch to LGA for some reason when Intel did and still hasn't.

For Intel chipset limitations on overclocking adhere to this guide: Intel chipsets that start with a P, Z, or X should allow multiplier changes to parts that don't have a locked multiplier and chipsets that start with an H (and I think Q) don't allow multiplier changes.

All AMD chipsets should allow multiplier changes to parts that don't have a locked multiplier.

 

[blazorthon]

Point is that RAM is not really significant for CPU overclocking anymore. If you have a system that needs to increase it's BLCK to get a decent overclock (for example, any CPU that isn't a Sandy Bridge CPU and has a locked multiplier) then you can lower the RAM multiplier so the RAM isn't getting to fast for it to handle itself while the CPU is increasing its frequency unrestrained by the RAM.

If a system has it's RAM running at the minimum speed but the RAM is still bottlenecking the CPU overclock then yes it would need better RAM but I don't think something like that is even remotely likely... Although it may be possible with systems that used early modules of DDR3 that can't go faster than 1066MHz because then it can only go down one multiplier notch from 2.67 to 2, meaning that the RAM would be overclocked too if the BLCK went over about ~260MHz. Such a problem would limit the BLCK to approximately a 30% overclock if the RAM can't stably go much faster than 1066MHz. Since many overclocks done on such computers (Nehalem, older AMD Athlon/Phenom IIs) would be limited until memory was upgraded the memory could be seen as a problem on multiplier locked CPUs that had to rely on the BLCK clock to get a large overclock.

This shouldn't be a problem for CPUs with an unlocked multiplier but many CPUs don't have one, such as non Black Edition Athlon/Phenom IIs and some Nehalem CPUs. I think the Nehalem i7s and non i7 K editions had unlocked multipliers but I never had a Nehalem machine. Machines with this early DDR3 and an unlocked multiplier weren't a problem with this because the multiplier could finish the overclock to whatever the desired/max clock rate was but without that unlocked multiplier better RAM was necessary.

 

[treyvon]

Best answer selected by Treyvon.