In­tel Core i7-7740X

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We’ll prob­a­bly never know whether In­tel’s ex­ten­sive X299 CPU line-up is due to AMD’s re­turn to form, or if In­tel was just try­ing to ex­tend its high-end desk­top plat­form’s reach, but there are some strange de­ci­sions in there none­the­less. Half the range is still miss­ing a cou­ple of months af­ter launch, with most of the top-end CPUs ar­riv­ing in Oc­to­ber. How­ever, the weird­est ad­di­tion of all are the two quad­core CPUs, one of which is the Core i7-7740X.

Ini­tially we thought the new CPUs might of­fer a cheap way of ac­cess­ing the ben­e­fits of In­tel’s X299 plat­form, such as the in­creased num­ber of PCI-E lanes or quad-chan­nel mem­ory. How­ever, as the i7-7740X is es­sen­tially just an LGA1151 CPU in LGA2066 guise, it can only of­fer 16 PCI-E lanes and lacks quad-chan­nel mem­ory sup­port too. The lat­ter is es­pe­cially ques­tion­able, as two-DIMM set­ups usu­ally need to be lo­cated in the right-side bank of four slots on an X299 mother­board, leav­ing the left side com­pletely blank, which looks de­cid­edly odd. The new quad-core CPUs also lack sup­port for Turbo Boost Max 3.

Like the cheaper Core i5-7640X, the Core i7-7740X is es­sen­tially a re­branded Kaby Lake LGA1151 CPU that’s shoe­horned into an LGA2066-size pack­age. Both CPUs are dubbed Kaby Lake-X to dif­fer­en­ti­ate them from the more ex­pen­sive Sky­lake-X CPUs, as they also use In­tel’s newer ar­chi­tec­ture. Oth­er­wise, the only real dif­fer­ence is clock speed. The Core i7-7700K is a lit­tle slower, with a base fre­quency of 4.2GHz and max­i­mum fre­quency of 4.5GHz, while the Core i7-7740X sits at 4.3GHz and 4.5GHz re­spec­tively, mak­ing it In­tel’s fastest quad-core pro­ces­sor.

All the cache lev­els are the same too, with the non-Hy­per-Threaded Core i5-7640X getting the usual 6MB L3 cache and the Core i7-7740X getting the same 8MB as the Core i7-7700K. An­other dif­fer­ence, though, is the TDP – the Kaby Lake-X CPUs both rise above their LGA1151 coun­ter­parts by 21W. Ba­si­cally, In­tel cre­ated the Core i7-7740X and Core i5-7640X purely for over­clock­ing en­thu­si­asts. The beefier power cir­cuitry on X299 moth­er­boards, com­bined with the CPUs’ use of the very lat­est 14nm sil­i­con, can po­ten­tially of­fer higher over­clock­ing head­room.

The prob­lem, of course, is that you’ll need an ex­pen­sive X299 mother­board just to net you a lit­tle more over­clock­ing head­room than you’d achieve with a Core i7-7700K and a Z270 mother­board. In terms of price, the new CPUs re­tail for roughly the same money as their main­stream coun­ter­parts. How­ever, with the 6-core Core i7-7800X re­tail­ing for just £40 more than the Core i7-7740X, and of­fer­ing four more threads, the Kaby Lake-X CPUs will be very niche.

Per­for­mance

We didn’t come across any per­for­mance sur­prises at stock speed; de­spite us­ing a com­pletely dif­fer­ent CPU socket, the num­bers were aligned with the sim­i­larly clocked Core i7-7700K. How­ever, the ad­van­tage in base fre­quency did al­low for some higher scores, with around 30 points added to Cinebench and a slightly higher sys­tem score. The higher clock speed didn’t add much to gam­ing per­for­mance, though, and the stock speed power draw was slightly higher for the Core i7-7740X.

Over­clock­ing was in­ter­est­ing in that we reached 5.1GHz very eas­ily with a vcore of just 1.28V, which is the amount most Z270 boards needed to reach just 5GHz with our Core i7-7700K. Tem­per­a­tures were well within lim­its here too, so we de­cided to push the vcore a lit­tle to see if we could get to 5.2GHz. It all seemed fine, ex­cept when you stressed all the cores in our video en­cod­ing test – even push­ing the vcore to 1.45V didn’t solve the is­sue, so we headed back to 5.1GHz for bench­mark­ing.

Not sur­pris­ingly, this over­clock also yielded some higher scores than our Core i7-7700K, with a 3,000-point ad­van­tage in the sys­tem score and the CPU top­ping 1,100 points in Cinebench.

Again, though, the dif­fer­ence wasn’t big enough for any mea­sur­able ad­van­tage in our game tests; how­ever, the Core i7-7740X in­ter­est­ingly drew less power from the wall un­der load when over­clocked than the main­stream CPU.

Con­clu­sion

Ul­ti­mately, both Kaby Lake-X CPUs are ques­tion­able ad­di­tions to In­tel’s line-up, given that they don’t of­fer many ad­van­tages. The main is­sue is that there aren’t any X299 moth­er­boards avail­able for un­der £200, while de­cent Z270

In­tel cre­ated the Core i7-7740X for over­clock­ing en­thu­si­asts

boards can be bought for un­der £160. Any small gains in over­clock­ing head­room will cost you at least £50 more once you fac­tor mother­board costs into the equa­tion. With ru­mours about 6-core Coffee Lake CPUs that are com­pat­i­ble with cur­rent Z270 moth­er­boards too, Kaby Lake-X is per­haps des­tined to fade from mem­ory as the CPU war con­tin­ues.

If our test sam­ple is rep­re­sen­ta­tive, the Core i7-7740X cer­tainly seems to of­fer more over­clock­ing head­room than the Core i7-7700K, and we imag­ine we’d be able to get fur­ther with cus­tom water-cool­ing and delid­ding the CPU. Gun­ning for the high­est fre­quency is still an at­trac­tive propo­si­tion too. The over­clocked Core i7-7740X’s sys­tem score of 162,570 is huge for a quad-core CPU and it wasn’t too far be­hind the 6-core Ryzen 5 1600X in Cinebench and video en­cod­ing either. Then again, though, it does cost £100 more than the Ryzen chip.

In short, the only peo­ple that should be con­cerned with Kaby Lake-X are ex­treme over­clock­ers. There are sim­ply far more at­trac­tive and bet­ter-value op­tions from both In­tel and AMD on the ta­ble right now, with more to come later in the year.

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