Intel Core i5 vs. Core i7: Which Processor Should You Buy?

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Whether you’re building your next PC or shopping for a new computer online, one of the questions that comes up from time to time is whether the Intel Core i5 or Core i7 is a better bargain. The short answer, “It depends,” isn’t all that helpful, so we’ve broken the data out in more detail and for both mobile and desktop processors. Intel’s 8th generation CPU launch and its decision to increase the core counts it offers in all three product families make this a particularly good time to revisit this discussion.

Desktop Core i5 vs. Core i7

Intel’s October 2017 update to the Core i5 (see on Amazon) and Core i7 (see on Amazon) are the first major shift in core counts since Sandy Bridge in 2011. For the past six years, Intel’s Core i5 family has offered four cores without Hyper-Threading, and the Core i7 family offered four cores with Hyper-Threading. Hyper-Threading allows two simultaneous “virtual” cores for each physical core and shares the workload between them.

The 8th-generation CPUs that Intel introduced in October 2017 increased the number of cores and threads within each of these families by 50 percent, and in the Core i7-8700K’s case, increased the core’s clock speed as well. Core i5 and Core i7 CPUs with model numbers beginning with an 8 (like the Core i7-8700K) now have six cores, or six cores + Hyper-Threading.

Intel-8thGen

Intel’s new 8th-gen processor lineup

Intel’s eighth-generation CPUs are generally more expensive than the CPUs they replace, though this varies somewhat. The overall price of CPUs in these segments has still come down on a per-core basis, and the performance boost from the additional cores is often worth it. If you aren’t sure what generation of Intel CPU you have, the first digit of the four-digit model code is the model number. If you have a Core i7-2600K, the “2” means this CPU is a second-generation Core i7 CPU, aka Sandy Bridge.

Intel’s decision to boost core counts across all three desktop CPU segments–the Core i3 also gets two cores and loses Hyper-Threading for a 4C/4T configuration–makes this an attractive time to buy. How much benefit you’ll see from upgrading depends to some extent on how much multi-threading your typical games or applications use and how old your current chip is. While there are still some single or dual-core applications out there, Windows is designed to spread multiple single-threaded workloads across multiple cores. A dual-core and quad-core application running at the same time will scale much better on the new Core i5 as opposed to the older variants.

While Microsoft’s DirectX 11 isn’t very good at taking advantage of multiple CPU cores, games can still use a mostly single-threaded approach for rendering while spinning audio, AI, and/or data loading on to their own threads. Gamers who stream and play games simultaneously from a single system may also find a six-core Core i5 much better-suited to the task than the 7th generation and earlier processors, though I don’t want to oversell this point until the two CPUs have been compared in gaming + streaming tests.

If all you care about is gaming and you don’t run any other workloads outside the game, an eighth-generation Core i5 won’t deliver much in the way of near-term benefits compared to the recent quad-core chips. Games don’t typically scale very much past four cores (4C/4T, as opposed to 2C/4T), though the newer DirectX 12 API could make gaming more multi-core friendly in the long term. If you’re a gamer on a 6th-or-7th-generation Core i5, an 8th-generation chip probably won’t improve your game performance much at the moment. If you’re going to upgrade no matter what, we’d recommend a newer, six-core i5 over the older quad-core variant. While I don’t generally recommend trying to “future proof” a system–it’s often not worth the premium you pay–CPUs now last long enough to make buying a core with an eye towards the future a reasonable decision.

i3-i5-i7-2

Intel’s new boxed packaging for the Core i3, i5, and i7 processors.

The 8th-generation Core i5 is a strong option for anyone who needs to balance multi-threaded performance, clock speed, and price. It won’t match the Core i7 in 3D rendering tests, video editing, or video encoding, but it’ll be just as fast as an equivalently-clocked Core i7 in games or in lightly threaded applications like Photoshop. Having six cores gives you some leg room if newer games begin taking better advantage of multi-threading. Alternately, it should also make it easier to stream and game on the same system, though I’d recommend consulting a separate guide that tests this use-case specifically before deciding on an 8th-generation i5 versus an i7.

The 8th-gen Core i7’s six cores and 12 threads are great for buyers who can take advantage of them. While Intel has been selling six-core CPUs for years, previous six-core chips were more expensive than the Core i7-8700K’s $359 MSRP, required generally more expensive motherboards, and required end-users to trade clock speed for core counts. It’s important, however, to make certain your applications can take advantage of all six cores and 12 threads before pulling the trigger on an 8700K.

What About Six-Core HEDT Customers?

Intel’s High End DeskTop market segment is, as the name suggests, Intel’s highest-end official desktop segment. These chips typically don’t support as much RAM as their Xeon counterparts and may lack other features like ECC RAM compatibility, but they historically offer more cores and threads than Intel’s mainstream Core i7s. For simplicity’s sake, we’re only comparing six-core HEDT processors against the Core i7-8700K. While Intel has previously sold HEDT CPUs with 8-10 CPU cores, we can’t make a simple rule of thumb for when an older HEDT CPU with a higher core count would be superior to the narrower, faster, Core i7-8700K.

If you’re using an early HEDT model, like the Core i7-3930K or Core i7-4930K, the 8700K will definitely be a step up. Both of those CPUs had all-core turbo clocks that were well below the Core i7-8700K’s 4.3GHz all-core frequency, and they used older, less-efficient architectures. Between the 8th-generation Core i7’s higher clock speed and higher efficiency, you can reasonably expect to see a 1.2x to 1.4x performance improvement depending on the workload, how high your previous CPU boosted under full load, and whether your applications take advantage of SIMD instruction sets like AVX2. Memory bandwidth-sensitive applications should also see a significant boost from the transition from DDR3-1600 to DDR4-2666. The age of your current HEDT system will matter significantly; customers with a 7800X or 6800K probably won’t see a benefit, while those with systems from the Ivy Bridge era or earlier will see significant, though not earth-shattering improvements.

If you’re one of the relative handful of customers using Intel’s first-generation six-core architecture, codenamed Westmere, you should definitely see a major performance boost from upgrading to the 8700K. Intel’s highest-end Westmere CPUs had full-core boosts below 3.7GHz in all cases and the old Nehalem architecture was markedly less efficient than Intel’s second-generation architecture, Sandy Bridge. Westmere also lacked support for capabilities like AVX and AVX2. The Core i7-8700K is clocked 1.3x higher than the old Core i7-980 and should offer at least 1.15x higher performance from architectural improvements alone. A 1.45x to 1.6x performance improvement from Westmere to Coffee Lake wouldn’t surprise us.

Putting It All Together

Intel’s decision to introduce higher core counts across its entire product stack means there’s some theoretical benefit to upgrading, even if you own a 7th generation CPU already. For practical purposes, however, we’re going to assume that most customers with a 6th-generation or 7th-generation CPU aren’t interested in buying a new motherboard and CPU so soon after their last update.

Chart-2A Chart-1A

We’ve thrown a lot of numbers and figures at this article, but don’t worry if you’re head is spinning a bit trying to keep it all straight. The slideshow above includes a number of charts intended to make it easier to grasp the improvements and value of upgrading depending on your current situation and product family.

Mobile Processors (8th Generation)

Up until late August, Intel’s mobile products were mostly dual cores across the entire Core i3 / i5 / i7 product stack. There were a handful of quad-core parts in the Core i7 family, but most of Intel’s mobile chips were 2C/4T configurations, with quad-core chips reserved for 45W TDPs and above. As of late August, Intel offers a handful of quad-core Core i7 and Core i5 CPUs. One major difference between these Core i5 chips and Intel’s entire previous lineup of Core i5 mobile processors is that the Core i5-8250U and Core i5-8350U do support Hyper-Threading. The Core i7 8650U and Core i7-8550U are also quad-core / eight-thread designs.

8th-Gen

Click to enlarge

Unfortunately, reviews of laptops that actually use these chips are still pretty few and far between, and Intel gives laptop manufacturers more leeway to specify their own desired operating temperatures and thermal limits in ways that can introduce substantial variation between different machines that ostensibly use the same processor. The early data on these chips suggests that they’re faster than the old dual-core variants, despite having much lower base clock speeds to compensate for the increased core and thread count, but no one has yet written a major review of any 8th-generation mobile system. None of the mobile CPUs announced thus far offer the onboard EDRAM cache that significantly improves Intel’s onboard graphics performance, either, while there are multiple 7th-generation SKUs that do.

Mobile Core i5 vs. Mobile Core i7 (7th Generation and Previous)

Mobile users have three distinct choices to make, which clouds the issue a bit. There are previous-generation Core M chips as well as Core i7 and i5 processors. The Core M chips are limited to the m3 family–Intel has taken what used to be a distinct brand and folded it into the Core i7 and Core i5 families instead. This creates situations like the one shown below.

Corei7-Comparison

These two chips look similar, with the same cache, almost the same clock speed, and similar GPUs–but they have different operating TDPs and hence offer different user experiences. Exactly how different isn’t something we can speak to without test hardware, but past systems showed marked variation depending on OEM design and thermal limits. Core M launched in 2014 but never sold particularly well–OEMs often saddle the processors with aggressive high-resolution displays and extremely thin chassis, leading to mediocre battery life.

The Core i5 is in a similar situation:

CoreM-Comparison

If you’re looking at the Core M-branded Core i5, we strongly recommend doing your homework and checking reviews of specific systems. Core M systems can deliver better battery life than their i5/i7 counterparts, but this will depend on the specifics of the manufacturer. Remember, high-resolution screens and ultra-thin systems with limited battery life will cost you just as much in power savings as you can get with a lower-TDP CPU–possibly more these days, since high-end chips account for a decreasing amount of power consumption.

The other major difference we want to discuss is the gap between 7th generation Core i7 and i5 core counts on mobile. Prior to Skylake (6th gen), almost all Intel chips on mobile were dual-core below the Core i7 level. There are a few 6th and 7th generation Core i5 mobile parts that offer quad cores without Hyper-Threading support, as shown below:

Intel-Core-i5-Mobile

The difference between these three cores is that one of them supports Intel’s Iris Pro Graphics, while the other two are Intel HD Graphics-only. The Iris Pro 580 is Intel’s only EDRAM-equipped 128MB Core i5. If you want a mobile processor with top-end graphics and a quad-core CPU, this is the Core i5 you want to purchase.

Outside of these three cores, the general rule does still follow. Most mobile Core i5 and all Core i3 processors are dual-core with Hyper-Threading. Here are the features that separate mobile Core i5 and Core i7 processors in 7th generation processors and below:

More cores: Many of Intel’s Core i7 processors are quad-core chips with Hyper-Threading enabled. This isn’t universal, however, and the company does offer a few dual-core + Hyper-Threading SKUs.

Higher clocks: Intel’s dual-core mobile Core i7 chips typically have higher clock speeds than their Core i5 counterparts, even at the same TDP.

More cache: Core i7 chips carry either 6MB or 4MB of cache. Core i5 chips run the gamut here. Older chips (pre-Broadwell) often carry 3MB, while Skylake and Kaby Lake chips are sometimes 4-6MB. The extra cache has only a small impact on performance.

More addressable memory: Many older mobile Core i7 and i5 processors are limited to 16GB of memory, but there are Skylake (6th-gen) chips that support 32GB and even 64GB on some late Core i5 / i7 models. 16GB of RAM is fine for the vast majority of users. But if you think you might need more, check what your CPU is capable of at Intel’s database.

How much performance you get out of a mobile Core i5 versus a Core i7 will depend a great deal on your laptop’s cooling solution and whether the chip can handle its own heat output. We’ve previously discussed how Intel gave OEMs more freedom to define their own TDP targets and skin temperatures. But this creates scenarios in which buying a faster Core M can actually result in worse performance, as the chip hits its thermal trip point and down-throttles to keep cool.

Intel's highest-end Iris Pro graphics are available in both Core i5 and Core i7 mobile SKUs

Intel’s highest-end Iris Pro graphics are available in both Core i5 and Core i7 mobile SKUs

We can’t point to specific instances where this has tilted performance between Core i5 and Core i7 chips, but it’s likely to create at least a little “slosh” between the two core families. Generally speaking, if you truly want to emphasize low power, pick the CPU that has lower base and turbo clocks. Intel historically defined TDP as “The CPU’s average power consumption when running typical workloads over a period of time.” A chip with more headroom is a chip that’ll hit its throttle point faster.

Which CPU Should You Buy?

If you’re looking at the mobile market, we’d recommend waiting to see how Intel’s quad-core Core i7 and Core i5 chips will compare to the older, higher-clocked dual-core variants before making a decision one way or the other. If you’re in the market for a desktop chip, on the other hand, the decision is fairly straightforward. Gamers and enthusiasts who want to balance high core counts and frequencies with a price below $300 should find the new Core i5 chips right up their alley. Only those looking for budget workstation performance or similarly demanding applications will benefit from the Core i7-8700K, but these workloads will be faster on Intel’s 8th-generation Coffee Lake than on any previous part. HEDT customers with older Westmere-era hardware should benefit a great deal from these improvements.

Those of you who want to see an equivalent document for AMD, don’t fret. That’s coming.

Now read: How to buy the right video card for your gaming PC

Check out our ExtremeTech Explains series for more in-depth coverage of today’s hottest tech topics.

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