Intel Core i5 vs. Core i7: Which processor should you buy?

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. Here’s what you need to know.

Mobile Core i5 vs. Mobile Core i7

Because Intel has launched a reasonable set of SKUs for its 5th generation (Broadwell) hardware, we’ll use those chips for comparing the Core i7 vs. Core i5 stack. All of Intel’s mobile Core i5 processors are dual-core chips with Hyper-Threading, going right back to Sandy Bridge. What distinguishes modern 5th generation Core i5s is their TDPs — Intel offers Broadwell in 15W, 28W, and a single 47W SKU. That chip, the Core i5-5350H is also capable of addressing 32GB of RAM and offers Intel’s Iris Pro 6200 solution based on Crystal Well.

Intel’s Core i5 mobile lineup (Broadwell)

Here are the features that separate mobile Core i5 and Core i7 processors:
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 five 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. The fastest dual-core Core i7 at 15W TDP is the Core i7-5600U, which runs at 2.6GHz base and 3.2GHz standard. The fastest Core i5 at 15W is the Core i5-5300U, which has a base clock of 2.3GHz and a max clock of 2.9GHz. The GPU on the Core i7-5600U is clocked 50MHz faster as well.

More cache: Core i7 chips carry either 6MB or 4MB of cache. Core i5 chips have 3MB, except for the Core i5-5350H, which has 4MB.

More addressable memory: Most of the Core i7 chips are limited to 16GB, like the Core i5, but there are four exceptions. The Core i7-5850HQ, 5950HQ, 5750HQ, and 5700HQ are all capable of addressing up to 32GB of RAM.

One important thing to note, however, is that how much performance you get out of a Core i5 vs. a Core i7 will depend a great deal on your laptop’s cooling solution and whether or not 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

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.

Desktop Core i5 vs. Desktop Core i7

Because Intel has only launched a handful of Core i5 and i7 desktop parts, for now we’ll focus on the 4th generation cores (Haswell). One significant difference between the desktop and mobile markets is that all but one of Intel’s 23 Core i5 SKUs offer four cores, but no HyperThreading. Intel’s Core i5-4570T is the single exception to this — it’s a dual-core + HyperThreading chip. Another difference between the mobile lineup vs. the desktop cores is that the desktop versions of both the Core i5 and Core i7 officially top out at 32GB of addressable memory.
In fact, many of the differences we observed between mobile parts don’t apply to desktop hardware. The i7 family still carries more L3 cache (8MB, save for the Core i7-4770R, which has 6MB), as compared to the Core i5 family, which has 6MB of cache on every chip except for the Core i5-4570R, 4570 and 4670R, which have just 4MB. Clock speeds are a mixed bag — while the fastest Haswell Intel manufacturers is the Core i7-4790K at 4GHz base clock and 4.4GHz Turbo, the Core i5-4690K is clocked at 3.5GHz base and 3.9GHz Turbo — essentially equal to the Core i7-4770K.
Both the Core i3 and Core i5 families use Intel HD Graphics 4600 solution with the same 350MHz base clock and 1.2GHz maximum clock. Apart from Hyper-Threading and some small cache differences, the Core i5 and Core i7 are quite similar, with overlapping frequency ranges and feature sets. Support for Intel’s TSX-NI instructions is only available on one Core i5 SKU, but only two Core i7’s offer the capability.
Similarly, Intel only offers vPro on 13 of the 23 Core i5 SKUs, compared to 9 of the 12 Core i7 SKUs — but if you want vPro on a Core i5, you can get it.