Intel Core i5-8400 vs Intel Core i7-7700K Comparison

FAQ

Q: Which processor has more cores, the Core i7-7700K or the Core i5-8400?

A: The Core i5-8400 has six physical cores, while the Core i7-7700K has four cores. However, the i7-7700K supports eight threads through Hyper-Threading, whereas the i5-8400 is limited to six threads.

Q: How do the two CPUs compare in single-threaded performance?

A: The Core i7-7700K leads in every recorded single-thread test. In Geekbench single-core, it scores 1547 against 1353 for the i5-8400, a 14.3% advantage. PassMark single-thread shows a 14.2% lead (2708 vs 2371), and Cinebench R23 single-core shows a 4.4% edge (1156 vs 1107).

Q: Which chip wins in multi-threaded workloads?

A: The Core i7-7700K wins all recorded multi-threaded benchmarks despite having fewer physical cores. In Cinebench R23 multi-core, it scores 8189 versus 7847 for the i5-8400, a 4.4% margin. Geekbench multi-core shows a 6% lead (5395 vs 5088).

Q: Are there any workloads where the Core i5-8400 is faster?

A: Yes, the i5-8400 wins three recorded tests: PassMark extended instructions (11543 vs 8943, a 22.5% advantage), PassMark find prime numbers (37 vs 31, a 16.2% edge), and PassMark floating point math (22006 vs 18741, a 14.8% lead).

Q: Do both processors use the same socket and memory type?

A: Both use Intel Socket 1151 and support dual-channel DDR4 memory. The i7-7700K has a memory bandwidth of 38.4 GB/s, while the i5-8400 has a higher 42.7 GB/s.

Q: Which processor has a higher boost clock?

A: The Core i7-7700K has a boost clock of 4.50 GHz, compared to 4.00 GHz for the Core i5-8400. The i7-7700K also has a much higher base clock at 4.20 GHz versus 2.80 GHz.

The Verdict

The benchmark data clearly favors the Intel Core i7-7700K in most scenarios. It wins 16 of the 19 recorded head-to-head comparisons, including every Cinebench test, both Geekbench tests, and the majority of PassMark workloads. Its strengths are most pronounced in integer math, encryption, and single-thread performance, where it leads by margins ranging from 14.2% to 19.5%. For users prioritizing raw single-core responsiveness, legacy software that relies on high clock speeds, or workloads that benefit from simultaneous multithreading, the i7-7700K is the stronger choice.

The Intel Core i5-8400, however, is not without merit. It wins in three specialized PassMark tests: extended instructions, prime number finding, and floating point math. The extended instructions result is particularly striking, with the i5-8400 scoring 22.5% higher, suggesting better execution of advanced instruction sets. The i5-8400 also offers a larger shared L3 cache (9 MB versus 8 MB), higher memory bandwidth (42.7 GB/s versus 38.4 GB/s), and a lower TDP of 65 watts compared to 91 watts. It was listed with a launch MSRP of $182, while the i7-7700K has no recorded launch MSRP in the database.

For a user who prioritizes multi-threaded throughput, encryption, or single-thread speed, the i7-7700K is the pick. For those who value energy efficiency, specific floating-point or extended-instruction workloads, and a more modern architecture, the i5-8400 is the better fit. The data does not support a universal recommendation; the choice depends entirely on workload profile.

Head-to-Head Benchmarks

The Core i7-7700K establishes dominance early in the Cinebench suite. In Cinebench R15 multi-core, it scores 825 versus 790 for the i5-8400, a 4.4% win. Single-core R15 shows a similar 4.5% margin (116 vs 111). The pattern repeats in R20, where the i7-7700K wins multi-core by 4.4% (3439 vs 3295) and single-core by 4.5% (485 vs 464). In R23, the i7-7700K continues with a 4.4% multi-core lead (8189 vs 7847) and a 4.4% single-core lead (1156 vs 1107). These consistent margins across three Cinebench versions indicate a stable performance advantage rather than a workload-specific anomaly.

Geekbench results amplify the i7-7700K's lead. The multi-core score of 5395 beats 5088, a 6% difference. The single-core gap is much larger: 1547 versus 1353, a 14.3% advantage. This suggests the i7-7700K's higher clock speeds, with boost up to 4.50 GHz versus 4.00 GHz, translate into outsized gains for lightly threaded tasks.

PassMark tests reveal a more nuanced picture. The i7-7700K wins data compression (136852 vs 129951, up 5.3%), data encryption (3343 vs 2824, up 18.4%), integer math (30553 vs 25573, up 19.5%), multithread (9627 vs 9225, up 4.4%), physics (655 vs 635, up 3.1%), random string sorting (17208 vs 15952, up 7.9%), and single-thread (2708 vs 2371, up 14.2%). These are substantial gains, particularly in integer math and encryption, which are often sensitive to per-core throughput.

The i5-8400 counters in three areas. PassMark extended instructions shows the largest swing: 11543 versus 8943, a 22.5% advantage for the i5-8400. This is the biggest margin in either direction across all recorded benchmarks. PassMark find prime numbers also favors the i5-8400, with 37 versus 31, a 16.2% edge. Floating point math goes to the i5-8400 as well: 22006 versus 18741, a 14.8% lead. These results suggest the i5-8400's newer Coffee Lake architecture handles certain mathematical and instruction-heavy workloads more efficiently, even with lower clock speeds.

Overall, the i7-7700K wins 16 benchmarks, while the i5-8400 wins 3. The i7-7700K's victories are more numerous and often larger in percentage terms, but the i5-8400's wins are not trivial, especially the extended instructions result.

Specification Differences

The two processors differ in several core specifications. The i7-7700K has 4 cores and 8 threads, while the i5-8400 has 6 cores and 6 threads. Base clocks diverge sharply: 4.20 GHz for the i7-7700K versus 2.80 GHz for the i5-8400. Boost clocks are 4.50 GHz and 4.00 GHz respectively. Thermal design power differs by 26 watts, with the i7-7700K rated at 91 watts and the i5-8400 at 65 watts.

Cache configurations are similar per core but differ in total L3. Both have 64 KB of L1 per core and 256 KB of L2 per core. The i7-7700K has 8 MB of shared L3 cache, while the i5-8400 has 9 MB. Memory bandwidth also differs: 38.4 GB/s for the i7-7700K, 42.7 GB/s for the i5-8400. Both support dual-channel DDR4.

Integrated graphics differ as well. The i7-7700K uses HD 630, while the i5-8400 uses UHD Graphics 630. The i5-8400 has a recorded die size of 154 mm²; no die size is recorded for the i7-7700K. The i7-7700K has an unlocked multiplier, while the i5-8400 is locked. Production status also differs: the i7-7700K is active, while the i5-8400 is end-of-life. The i5-8400 has a launch MSRP of $182; the i7-7700K has no recorded launch MSRP.

Architecture Differences

The i7-7700K is built on the Kaby Lake architecture, while the i5-8400 uses Coffee Lake. Both are manufactured by Intel on a 14 nm process node, but they represent different architectural generations. The i7-7700K belongs to the Core i7 (Kaby Lake) generation, and the i5-8400 belongs to the Core i5 (Coffee Lake) generation.

The core count difference is a direct result of the architectural shift. Coffee Lake brought more physical cores to mainstream desktop processors, giving the i5-8400 six cores compared to the i7-7700K's four. However, the i7-7700K compensates with Hyper-Threading, allowing eight threads versus six for the i5-8400. This thread advantage helps explain why the i7-7700K still wins multi-threaded benchmarks despite having fewer physical cores.

Clock speed strategy also differs. The i7-7700K is a high-frequency design with a 4.20 GHz base clock, while the i5-8400 uses a lower base clock of 2.80 GHz but boosts to 4.00 GHz. The i7-7700K's unlocked multiplier suggests it is positioned for enthusiast overclocking, whereas the i5-8400's locked multiplier targets mainstream users.

Cache allocation reflects the core count difference. Both chips give each core 64 KB of L1 and 256 KB of L2, but the shared L3 is larger on the i5-8400 at 9 MB versus 8 MB. This slightly larger pool of shared cache may contribute to the i5-8400's wins in extended instructions and floating point math.

Memory bandwidth favors the i5-8400, with 42.7 GB/s versus 38.4 GB/s. The i5-8400 also has a smaller die size of 154 mm², though no die size is recorded for the i7-7700K. Both processors use the same socket, PCIe configuration (Gen 3, 16 lanes CPU only), and lack ECC memory support. The i5-8400's newer architecture and lower TDP make it a more power-efficient design, while the i7-7700K leverages higher clocks and threading to win the majority of recorded benchmarks.