Understanding Clock: Processor Base and Boost Speeds

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When you’re in the market for a processor, there is a list of things you should be considering. Traditionally, pretty much the only thing most consumers look at is its total Gigahertz power. Many of those people probably don’t even know what it means (it’s the number of clock cycles—effectively, calculations—a processor completes in one second, in billions; referred to as a system’s clock speed), but it’s an easy thing to compare. If you’re buying a laptop and can choose the processor you want, you can assume, generally, that the one rated at 2.5 GHz is probably faster than the one rated at 2.3 GHz.

The past few years have brought an added wrinkle: Boosting speed. Most processing units, graphical and computational, now have a base clock speed and a boost speed. Intel® calls this Turbo Boost; AMD calls it Turbo Core.

So what does all this mean? More importantly: What does it mean for you? First, let’s talk about the purpose of a “base” clock speed. The faster your processor runs, the more power it requires and the more heat it generates. Take, for example, the Intel® Core™ i7-5820K. It’s a 6-core CPU with a base clock speed of 3.3 GHz and a Turbo Boost speed of 3.6 GHz. For the most part, you want your processor to be running at that slower speed. Basic tasks don’t need a 3.6 GHz processor to run. Indeed, most of them don’t need 3.3 GHz. So, in moments when you don’t need the higher speed, why would you want to raise your power bill and generate extra heat?

For a long time, over-clocking was for enthusiasts only. Over-clocking is a process that takes a capable processor and changes its clock multiplier. Every CPU has a low-level clock that is multiplied in order to reach the number we all know. A CPU with a 300 MHz low-level clock and an 11x multiplier has an effective clock speed of 3.3 GHz. With the right processor, you can change that multiple, thus over- (or under-)clocking your processor. But while the hardest of the hardcore would use liquid nitrogen coolers to break over-clocking world records, most people would be stuck with the number on the box.

These Turbo modes are essentially over-clocks for the masses, but you don’t choose the speed; the system does. When your computer realizes that it needs more clock cycles (say, when you’re trying to render a video), then it will crosscheck the need for speed with its temperature. If it’s cool enough, that means there’s thermal overhead for it to over-clock, at which point it will bring itself up to the boost speed. How long it lasts depends both on how long the system feels it needs to boost, and also whether or not it continues to be reasonably cool.

But it’s worth noting that that top clock speed is for one processor. If you’re running a program that only uses a single processor, then you’ll get that full boost. But if you’re using all available cores (six, in the case of the 5820K), they don’t all boost to that maximum speed. One core would hit 3.6, but all six might only go up to 3.4 GHz when Turbo Boost is activated. (This also depends on your motherboard, and high end/enthusiast motherboards will allow these numbers to go higher than low-end ones.)

With phones, things are a little bit different. More often than not, the manufacturer won’t even tell you what a chip’s base clock speed is, because it’s a number that more or less won’t tell you anything about the chip itself. Under normal conditions, your desktop processor will run at its base speed. A phone, on the other hand, will pretty much never run at that speed. That’s because the base speed on ARM chips, which power nearly every mobile device on the market, is just a few hundred megahertz. But this allows them to run in an idle state with minimal power draw/heat generation.

This base clock speed will never be in effect during actual use. When your phone turns on, the processor screams into action and runs right up around that promised speed. How long it stays there, however, is frequently down to the manufacturing of the phone itself, because as the processors overheat, they throttle themselves. This is true of most processors, but depending on how aggressively it’s done, you may have two phones with identical chips that run at effectively different clock speeds.

Such was the case in 2013 when Google’s Nexus 5 was found to throttle itself heavily due to structural heating problems caused by the phone’s design. A phone with a plastic chassis is more likely to overheat than one with a metal chassis (premium components aren’t just about looking pretty), and phones that don’t dissipate heat particularly well simply won’t run at the same speeds as better-designed phones.

In general, take the boost speeds as a guideline rather than a rule. On a desktop, you never have to worry about your computer running below its base speed (unless you want it to), but on a mobile device with heat and battery-power constraints, it’s more complicated. You aren’t likely to see a phone running at 600 MHz, but that 1.7 GHz processor may, in actuality, be a bit more like a 1.3 GHz processor with the occasional 400 MHz boost. Unfortunately, it’s nearly impossible to know without independent verification where any given system might fall, and the benchmarks that many reviewers run can’t necessarily take this variability into account.

Modern laptops are in a similar place to phones. A new MacBook Air, for example, has a 1.6 GHz Intel Core i5 with a 2.7 GHz boost speed. This allows for the best tradeoff between performance and battery life but, as with phones, laptops have lesser cooling systems than desktop chips, meaning they can’t necessarily sustain those boosted speeds.

If you know your priorities, then you can know what you need. Do you want lower heat generation and power draw/higher battery life but the ability to spike if needed? Look for a processor with a more impressive boost but a lower base speed. Want the ability to overclock it even further? Look for a system with an “unlocked multiplier.” Intel marks those processors with a “K” and AMD with an “FX.” And when you’re choosing a phone, see if there are any outlets that have reported throttling issues on a particular model. Don’t just take the manufacturer’s word for it.

Also, don’t focus exclusively on a clock speed. It’s a helpful metric when comparing different versions of the same processor line, but a 4 GHz AMD CPU is not necessarily more powerful than a 3.5 GHz Intel CPU. Even comparing a modern Intel chip to an older one doesn’t tell you much. A single clock cycle is now far more efficient than it was in the past, so nearly any Intel Core chip is more powerful than any chip from the Pentium days.

And that’s why benchmark tests exist, because they’re the only way to compare performance directly across brands and product lines. There are basically two types of benchmarks: conceptual and practical. Those aren’t official designations, but they get at the underlying point. A conceptual benchmark is specifically and exclusively a benchmark. It’s a specific program that might run in your browser or as its own executable. These output scores can be used to compare processors directly, though they aren’t particularly meaningful in and of themselves. What does the 5820K’s Cinebench R15 single threaded score of 140 mean, or its multi-threaded score of 1,025? And what does it mean that the 5930K gets scores of 146 and 1,083 respectively? Are those slightly higher numbers worth the $200 premium over the 5820K? Some benchmarks test how quickly a system will run the benchmark, and though many of these try to simulate real-world use, the scores don’t necessarily mean much. How would a 10 or even a 100 ms difference in the speed it takes to complete the web benchmark Mozilla Kraken affect your actual experience? It will most likely be a little bit faster, but it’s hard to really know.

Practical benchmarks use programs to do specific tasks—for example, rendering a video or compressing a series of files. Anandtech’s WinRAR test compresses 2,876 files—totaling 1.52GB—and times it. The 5820K completes this task in 46.17 seconds. The 5930K finishes it in 44.95. The $1,000+ 5960X completes it in 34.25. Even though those first two numbers are close, they’re easy to understand. The more expensive chip is slightly faster (as it should be), and the $1,000 monster crushes both of them (as it should). Conversion of a video file might be measured in frames per second, which is also easy to understand. These numbers are more helpful in and of themselves, as they reflect actual-use cases. But, as with anything, benchmarks aren’t all you have to consider. And, of course, benchmarks aren’t all you have to consider. All three of these chips are Intel’s Haswell-E system, but the 5960X has eight cores and a 20MB cache; the other two have only six cores and 15MB. The 5820K has only 28 PCIe lanes and the others have 40. The latter, in particular, is unlikely to show up in many benchmarks, and it’s the slightly lower clock speed of the 5820K (3.3-3.6) versus the 5930K (3.5-3.7) that explains its weaker showing, not the lesser bandwidth.

It is important to keep all this in mind, as an informed consumer is an empowered consumer. It’s nice to have a solid base clock, and it’s even nicer to have a high boost speed. They are certainly crucial in determining what you want and need from your new CPU, but they should count as just one of the things you take into consideration. 

Quality Pro Con
High overall clock speed Faster More power required
More heat generated
Low base clock (with high boost) More efficient Greater potential for throttled performance
Better battery life (portable devices)
Unlocked multiplier (over-clockability) Ability to increase system performance More expensive
Requires better cooling
Multi-core Better multi-threaded performance Often worse single-threaded performance 
Larger
Hyperthreading Effectively doubles the number of processor cores accessible by optimized programs Most programs aren't optimized
More expensive
Integrated graphics on chip No need for dedicated GPU Not all chips have them, which isn't really a con, just true

9 Comments

Which will be more fast a processor having base frequency of 4.0 Ghz and L3 cache of 8 Mb with 4 cores or a processor having base frequency of 3.6 Ghz, L3 cache of 15 Mb and 6 cores?

The speed and effectiveness of the processor would typically depend on the program you're using.  But generally speaking, the processor with a higher L3 cache and 6 cores would be a better performing processor.

It's also noteworthy to consider the L3 cache, for example a 3.5Ghz CPU with 8MB L2 & 8MB L3 will outperform one of the same GHz level that has 2MB L2 & 4MB L3 cache (which is the memory of the CPU. 

This ia another reason that old school 3.33GHz dual core Core2Duo (E8600) is slower, despite having a higher base clock speed, there's no L3 cache, and the L2 is 6MB. While good for it's day, that time has came & gone. Even the best consumer grage Intel Core2Quad 9650 has a 12MB L2, but still no L3, and why the much lower priced FX-6300 (even with a crippled core that cannot be unlocked will be faster. 

So keep in mind to check out the L3 cache of a CPU before purchase, it could well be that one that has a slightly lower GHz level will outperform the other, because of more inbuilt memory. 

One thing that the article didn't note, was that even the most entry level 6 core Intel CPU, though runs at a far less GHz level than say the quad core i7-4790K, has almost double the L3 cache. They're not selling these chipos for the sake of it, if these were no good, then many would go with a i7-4790K or 6700K for the 4.0GHz base speed, and 4.4GHz turbo for the 4790K, 4.2GHz Turbo for the 6700K. 

I stated it then, and was talked out of it, now wished had never raised the discussion, because not only does the i7-5820K have the 15MB L3 cache, also allows for more on board accessories then the i7 quad options, due to 28 lanes for PCIe devices, versus 16 lanes for the 4790/6700K. This is a lot more room for expansion, and on up the latter, some of the higher priced models has 40 lanes. 

So there's more to consider, based on needs, some may require the i7-5820K for the extra PCIe lanes alone, and the 15MB cache will make the CPU more responsive than it's bare GHz level shows it to be. Example, there's at least one 3.8Ghz 1150 i3 CPU (don't know the model number offhand, seen on a competing site, no way can hold a candle to the 5820K. 

That's my two cents worth.;-)

Cat

It's also important to note that Windows makes use of "Power Profiles" which are quite easy to make heads and tails of even for the uninitiated.

There are often three defaults active out of the box, performance, power saver, and balanced. These are usually most important on laptops. For example, when plugged in the balanced or performance settings will be used. When running on the battery you either get power saver or balanced. These are just easy power plans but each contains two modes on most settings that you can adjust separately so different power plans don't need to be selected, battery and plugged in.

But these aren't just for laptops. If you click on the advanced tab or option you will be presented with a wealth of options, most of which are explained quite well on the web. A partial list includes how much inactivity (if any, any time related settings can be disabled) it takes before the computer sleeps, hibernates, screen saver activation, for the monitor to shut off(which usually includes the graphics card as well), for hard disks to stop spinning, etc. As noted above, on a laptop everyone of these has two components: battery power and plugged in. 

I suggest doing some googling regarding power plans for most settings if you're not sure what to adjust.

But a relatively simple power vs performance adjustment is the minimum and maximum CPU settings. Under the performance plan both values will be 100%. But these can be adjusted from 5-100%. So if you're transcoding a video that may take a couple hours to complete you set the max to 100 and the min to 25. It will run at max performance until done and then drop down to the set min, or somewhere in between of the computer is performing other tasks.

One thing to nnote is that of you're sitting at computer this setting can cause you to tear your hair out because the computer does change this on the fly, and seemingly simple tasks may feel like they're occurring at a snails pace.

There is another setting to worry about called speed step that it's enabled or disabled in the bios. Again, Google is your friend. This can also be a make you crazy setting, although admittedly I'm not sure if it still exists on newer Intel computers. Basically, when enabled, the bios gives complete control to the OS to "speed step" the CPU. It does this by automatically adjusting the clock multiplier mentioned in the article. 

Now, you can go into any one of the included power profiles and adjust things to your hearts content. The easiest way is to create a new profile based on one of the defaults. But you can also mess with a default plan to see what changes affect your computing. This is possible because of the all important "reset to defaults" option. You can also mess with one of the defaults and save it to another name, then reset whatever plan you were in back to its default state.

This is just a qquick overview on how you can have a monster rig but still save power when you don't need it.

Just put on your Google hat, and play around. As mentioned it's pretty impossible to mess anything up because of the reset to default savior. 

I have i5 processor 5th gen with 1.6Ghz and 2.7Ghz turbo boost.plz rank it...

On the chart above that processor would fall into the Low base clock (with high boost) area. Great for battery life, and generally more than sufficient for the average user. It will not however keep up with continued high demand without throttled clock speed.

Sorry for the late reply but: doesn't that only apply if the cooler can't dissipate that's coming from the processor? otherwise it would be able to run on boost at all times right?

Hi Anthon - 

In short, it's best not to run the CPU at full, or near full capacity for long periods of time. Even with a great heat sync, it will shorten the lifespan of the CPU.

I think it's worth mentioning how easy it is to overclock now, with just a basic understand of PC building. A $50 self contained water cooler could be the difference of .5 Ghz, that is no harder to install then it is to hang a picture frame. Especially with the 5920k, 5930k, and 5960X.

I have my 5920k running at, 4.3 Ghz stablely. Thats nearly 25% faster than the base clock, which goes a VERY long way for editing. Something anyone interested in getting the most for you money we looking for a edit rig should consider.

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