CPU Comparison

The AMD Ryzen Threadripper 3990X and the Intel Core i5-8400 sit on opposite ends of the desktop computing spectrum, yet their average benchmark scores are remarkably close: 12786 for the AMD part and 12765 for the Intel part, a delta of just 0.2%. This parity is an illusion, however, as the average is skewed by the 3990X’s lower single-threaded scores being balanced against its massive multi-threaded lead. The head-to-head data reveals a complete sweep: the 3990X wins all 8 direct comparisons, with the Intel part failing to take a single benchmark. The most significant victories are in heavily threaded workloads, where the 64-core, 128-thread AMD processor utterly dominates the 6-core, 6-thread Intel chip.

Head-to-Head Benchmarks

The most lopsided results appear in Cinebench multi-core tests. In Cinebench R15 multi-core, the 3990X scores 6866 against the i5-8400’s 790, a staggering 769.1% advantage. This pattern holds across every Cinebench iteration: R20 multi-core shows a 768.3% delta (28612 vs 3295), and R23 multi-core shows a 768.2% delta (68124 vs 7847). The consistency of these deltas, all hovering near 768-769%, indicates that the performance gap scales almost perfectly with thread count, as the 3990X offers 128 threads versus the i5-8400’s 6, a 21.3x difference in thread availability that translates into roughly an 8.7x performance multiplier in these render workloads.

Surprisingly, the 3990X also wins single-core Cinebench tests by wide margins, though these numbers warrant scrutiny. In Cinebench R15 single-core, the 3990X scores 969 versus the i5-8400’s 111, a 773% delta. R20 single-core shows 4039 vs 464 (770.5%), and R23 single-core shows 9617 vs 1107 (768.7%). These deltas are nearly identical to the multi-core results, which is unusual, it suggests the i5-8400’s single-core scores in this dataset are anomalously low relative to its multi-core performance. The Geekbench single-core result is more realistic: the 3990X leads 1472 to 1353, a modest 8.8% advantage. This is the only head-to-head benchmark where the gap is below 300%, indicating that the 3990X’s Zen 2 architecture does provide a genuine per-clock advantage over the older Coffee Lake design, though not the 7.7x delta the Cinebench numbers imply.

Geekbench multi-core provides a more moderate but still decisive win: 20912 vs 5088, a 311% delta. This benchmark likely scales across all available threads but with less efficiency than Cinebench’s render engine, yet the 3990X still delivers over four times the score. The data shows a clear pattern: the 3990X wins by 768-773% in Cinebench (both single and multi-core), by 311% in Geekbench multi-core, and by only 8.8% in Geekbench single-core. The Intel part’s best relative performance is in single-threaded integer work, where it trails by less than 10%, but it offers no competitive threat in any threaded scenario.

The Verdict

From the benchmark data alone, the choice depends entirely on workload. The AMD Ryzen Threadripper 3990X is the definitive winner in every direct comparison, sweeping all 8 head-to-head benchmarks with zero wins for the Intel Core i5-8400. For any application that scales with core count, rendering, video encoding, scientific simulation, or virtual machine hosting, the 3990X’s 64 cores and 128 threads provide a 311% to 769% performance advantage depending on the test. The Cinebench R23 multi-core score of 68124 versus 7847 indicates a workload that takes roughly 8.7 times longer on the i5-8400, a difference that transforms hours-long renders into minutes-long tasks.

The Intel part is not without merit, but its strengths lie outside the benchmark set. The i5-8400 has integrated UHD Graphics 630, a feature the 3990X lacks entirely, making it usable without a discrete GPU. Its 65W TDP versus the 3990X’s 280W TDP suggests far lower power draw, though the fact pack provides no wattage measurements to quantify this. The i5-8400 also uses dual-channel memory with 42.7 GB/s bandwidth, while the 3990X uses quad-channel with 102.4 GB/s, but the Intel part’s lower platform cost might appeal to users who do not need extreme throughput. However, strictly from benchmark scores, the 3990X wins every test. The i5-8400’s only consolation is its 68th percentile ranking among all CPUs, tied with the 3990X, indicating that its average score across all benchmarks is competitive, but this average masks the fact that the i5-8400’s PassMark scores (not available for the 3990X) likely boost its standing.

Architecture Differences

The two processors come from fundamentally different design philosophies. The AMD Ryzen Threadripper 3990X uses the Zen 2 architecture, codenamed Castle Peak, built on TSMC’s 7 nm process with 30,400 million transistors across a die size of 8x 74 mm². The Intel Core i5-8400 uses the Coffee Lake architecture on Intel’s 14 nm process, with a 154 mm² die and no transistor count listed. The node difference is significant: 7 nm versus 14 nm allows the AMD part to pack 64 cores into a power envelope of 280W TDP, while the Intel part manages only 6 cores within 65W TDP.

Cache configurations diverge sharply. The 3990X offers 64 KB L1 and 512 KB L2 per core, with a massive 256 MB L3 cache. The i5-8400 also provides 64 KB L1 per core but only 256 KB L2 per core, and its L3 is 9 MB shared across all six cores. The 3990X’s L3 cache is 28.4 times larger, which helps feed its 128 threads. Memory support differs in channel count: the 3990X uses quad-channel DDR4 with 102.4 GB/s bandwidth, while the i5-8400 uses dual-channel DDR4 with 42.7 GB/s. PCIe capability also diverges: the 3990X supports Gen 4 with 64 lanes (CPU only), while the i5-8400 supports Gen 3 with 16 lanes.

Socket compatibility is a key differentiator. The 3990X requires AMD Socket TRX4, while the i5-8400 uses Intel Socket 1151. The 3990X has an unlocked multiplier, allowing overclocking, whereas the i5-8400’s multiplier is locked. The AMD part’s base clock is 2.90 GHz with a boost of 4.30 GHz; the Intel part starts at 2.80 GHz and boosts to 4.00 GHz. Neither supports ECC memory. The 3990X has no integrated graphics, while the i5-8400 includes UHD Graphics 630. Production status favors the AMD part (Active) over the Intel part (End-of-life), and release dates show the i5-8400 launched in October 2017, over two years before the 3990X’s February 2020 debut.

FAQ

Q: Which processor has more cores and threads?

A: The AMD Ryzen Threadripper 3990X has 64 cores and 128 threads, while the Intel Core i5-8400 has 6 cores and 6 threads. This 58-core and 122-thread difference drives the multi-core benchmark deltas of 311% to 769%.

Q: Is the Threadripper 3990X faster in single-core workloads?

A: Yes, according to the data. The 3990X wins all single-core Cinebench tests by about 768-773% and Geekbench single-core by 8.8%. The Geekbench result is a more realistic measure of per-core performance.

Q: What is the L3 cache size on each processor?

A: The 3990X has 256 MB of L3 cache, while the i5-8400 has 9 MB shared. The 3990X also has 512 KB L2 per core versus 256 KB per core on the i5-8400.

Q: Does the i5-8400 have integrated graphics?

A: Yes, the i5-8400 includes UHD Graphics 630. The 3990X has no integrated graphics, requiring a discrete GPU for display output.

Q: Which processor supports more memory bandwidth?

A: The 3990X supports quad-channel DDR4 with 102.4 GB/s bandwidth. The i5-8400 supports dual-channel DDR4 with 42.7 GB/s bandwidth.

Q: What are the production statuses of these CPUs?

A: The 3990X is listed as Active, while the i5-8400 is End-of-life. The i5-8400 was released in October 2017, and the 3990X in February 2020.

Where Each One Wins

The AMD Ryzen Threadripper 3990X wins in every benchmark category where both processors have direct comparison data. Its largest margins come in Cinebench multi-core tests, where it delivers 768-769% higher scores, translating to roughly 8.7 times the render throughput. In Geekbench multi-core, it wins by 311%, indicating strong scaling in general-purpose multi-threaded applications. Even in single-core tests, it maintains an edge, from 8.8% in Geekbench to 768-773% in Cinebench, though the Cinebench single-core figures appear outlier-high. Users running CPU-bound renderers, compilers, or data-processing pipelines that saturate 128 threads will see transformative gains.

The Intel Core i5-8400 has no benchmark wins in the head-to-head data, but its qualitative advantages are clear. Its integrated UHD Graphics 630 means it can power a display without a dedicated GPU, making it suitable for basic office systems or media PCs where the 3990X’s lack of iGPU would be a dealbreaker. Its 65W TDP versus 280W suggests substantially lower power draw, which may favor small-form-factor builds or systems where cooling is constrained. The i5-8400’s dual-channel memory and 16 PCIe Gen 3 lanes are sufficient for mainstream workloads, and its locked multiplier simplifies system configuration. For users whose workloads do not exceed 6 threads, such as light web browsing, document editing, or legacy single-threaded applications, the i5-8400 provides adequate performance at a fraction of the platform complexity, though the benchmark data offers no direct comparison for such tasks.