AMD Ryzen 5 8400F vs AMD Ryzen 7 7840U Comparison

The AMD Ryzen 7 7840U and the AMD Ryzen 5 8400F are an unusual pairing: two chips cut from the same silicon family, sharing the Zen 4 architecture, the Phoenix codename, TSMC's 4 nm process, and even an identical 25,000 million transistor count on a 178 mm² die. Yet the database shows them playing entirely different roles. The 7840U is a mobile part built around a 28 W TDP with integrated Radeon 780M graphics, while the 8400F is a 65 W desktop chip on Socket AM5 with no integrated graphics at all. Across the head-to-head records the 8400F wins 16 tests to the 7840U's 5, but the margin story is far more nuanced than that tally suggests, and a handful of the 7840U's wins are substantial.

Architecture Differences

At the silicon level these two processors are siblings. Both use AMD's Zen 4 microarchitecture under the Phoenix codename, both are fabricated by TSMC on a 4 nm node, and both carry 25,000 million transistors on a 178 mm² die. The cache hierarchy is identical too: 64 KB of L1 per core, 1 MB of L2 per core, and a shared 16 MB L3 slice. Neither part offers 3D V-Cache.

The divergence begins with core topology and target platform. The Ryzen 7 7840U is an 8-core, 16-thread mobile processor for Socket FP8, with a 3.30 GHz base clock, a 5.10 GHz boost clock, and a 28 W TDP. The Ryzen 5 8400F is a 6-core, 12-thread desktop processor for Socket AM5, with a higher 4.20 GHz base clock, a lower 4.70 GHz boost ceiling, and a 65 W TDP. That clock profile reflects their design intent: the desktop part holds higher sustained frequencies under a generous power envelope, while the mobile part chases peak single-thread bursts within a thin-and-light thermal budget.

Platform features split further. The 7840U integrates Radeon 780M graphics, supports ECC memory, and delivers 89.6 GB/s of memory bandwidth over its dual-channel DDR5 interface. The 8400F has no integrated graphics, lacks ECC support, and posts slightly lower memory bandwidth at 83.2 GB/s, also on dual-channel DDR5. Both expose PCIe Gen 4 with 20 CPU lanes. One notable differentiator for tinkerers: the 8400F ships with an unlocked multiplier, whereas the 7840U does not. The 8400F's recorded release date is March 31, 2024, with a launch MSRP of $170; the database holds no release date for the 7840U.

Where Each One Wins

The Ryzen 5 8400F dominates the rendering and physics workloads that reward sustained clock speeds and a desktop power budget. Its Cinebench R23 results are the standout: 20851 multi-core against 12719 for the 7840U, a 39% gap, and 2943 single-core against 1677.5, a 43% gap. Those are the two largest margins in the entire dataset and they point to a consistent cause, namely the 8400F's ability to hold high clocks under load where the 28 W mobile part must throttle. The 8400F also sweeps every 3DMark CPU test, from single-thread (951 versus 932) through max threads (6165 versus 5402), and takes Cinebench R15 in both single-core (296 versus 264) and multi-core (2101 versus 1990) runs. Passmark physics, prime finding, string sorting, extended instructions, and single-thread tests all fall its way as well.

The Ryzen 7 7840U's victories cluster in computational throughput tests where its extra two cores overcome its lower clocks. It wins Passmark integer math by 22.7% (90852 versus 74021), floating point math by 12% (51767 versus 46217), and data encryption by 6.3% (17691 versus 16646). Data compression is effectively a tie that technically goes to the 7840U, 288604 versus 288158, a 0.2% edge. Its narrow 1.6% win in Passmark multithread (24782 versus 24389) is the most telling single number in the dataset: with all threads loaded, the 8-core mobile chip and the 6-core desktop chip land within rounding distance of each other. In practical terms, the 7840U is the pick where integer-heavy computation, encryption throughput, or a self-contained mobile platform with integrated graphics matters, and the 8400F is the pick for rendering, gaming-adjacent CPU physics, and bursty desktop workloads.

Specification Differences

The fields where these two chips differ, and only those, are as follows. Cores and threads: 8/16 for the 7840U versus 6/12 for the 8400F. Base clock: 3.30 GHz versus 4.20 GHz. Boost clock: 5.10 GHz versus 4.70 GHz. TDP: 28 W versus 65 W. Socket: FP8 versus AM5. Series: 7000 versus 8000. Market segment: Mobile versus Desktop. Integrated graphics: Radeon 780M versus none. ECC support: yes versus no. Memory bandwidth: 89.6 GB/s versus 83.2 GB/s. Multiplier: locked versus unlocked. Everything else in the records, architecture, codename, process node, foundry, transistor count, die size, cache at every level, DDR5 support, dual-channel bus, PCIe Gen 4 with 20 lanes, and Active production status, is shared.

FAQ

Q: Which CPU is faster overall?

A: The aggregate scores are nearly identical. The 7840U posts an average benchmark score of 25432 against 25005 for the 8400F, and both sit at the 77th percentile versus all CPUs in the database. The 8400F wins more individual tests (16 to 5), but the 7840U wins some of the biggest ones.

Q: How do they compare against other CPUs?

A: The 7840U's nearest rivals include the Intel Core i7-11700KF (25423, delta 0%), AMD Ryzen 7 5825U (25446, -0.1%), Ryzen 5 7640U (25485, -0.2%), and Ryzen 5 5600X3D (25365, 0.3%). The 8400F lines up against the Ryzen 5 7500F (24964, 0.2%), Intel Core i7-11850H (24935, 0.3%), Core i7-13620H (24911, 0.4%), and EPYC 9474F (25103, -0.4%).

Q: Which one is better for rendering?

A: The 8400F, decisively. It leads Cinebench R23 multi-core by 39% and Cinebench R23 single-core by 43%, and also wins Cinebench R15 in both categories.

Q: Does either chip have integrated graphics?

A: The 7840U includes Radeon 780M graphics. The 8400F has none, so it requires a discrete graphics card.

Q: Can either CPU be overclocked?

A: The 8400F has an unlocked multiplier. The 7840U's multiplier is locked.

Q: Do they support ECC memory?

A: The 7840U does. The 8400F does not.

Head-to-Head Benchmarks

The 8400F's headline wins come from the Cinebench suite. In Cinebench R23 single-core it scores 2943 against 1677.5 for the 7840U, a 43% margin, and in R23 multi-core it scores 20851 against 12719, 39% clear. Cinebench R15 repeats the pattern at smaller scale: 296 versus 264 single-core (10.8%) and 2101 versus 1990 multi-core (5.3%). The 3DMark CPU profile is a clean sweep for the desktop chip across every thread count: 951 versus 932 single-thread (2%), 1874 versus 1729 at 2 threads (7.7%), 3563 versus 3029 at 4 threads (15%, the largest 3DMark gap), 5275 versus 4583 at 8 threads (13.1%), 6091 versus 5427 at 16 threads (10.9%), and 6165 versus 5402 at max threads (12.4%). Passmark side tests mostly favor the 8400F as well: physics 1332 versus 1256 (5.7%), string sorting 34604 versus 33757 (2.4%), single-thread 3685 versus 3565 (3.3%), prime finding 89 versus 80 (10.1%), and extended instructions 22175 versus 20432 (7.9%).

The 7840U's counterattacks are concentrated but meaningful. Its best result is Passmark integer math, 90852 versus 74021, a 22.7% win driven by the two extra cores. Floating point math goes its way 51767 to 46217 (12%), and data encryption 17691 to 16646 (6.3%). Data compression is a statistical dead heat, 288604 versus 288158, with the 0.2% edge to the 7840U. Most instructive is Passmark multithread: 24782 for the 7840U against 24389 for the 8400F, a 1.6% win for the mobile chip. When a workload scales across all available threads without demanding peak per-core frequency, the 8-core Phoenix at 28 W essentially matches the 6-core desktop Phoenix at 65 W.

The verdict the data supports is a split by workload rather than a single winner. The 8400F is the stronger renderer and the stronger burst performer, with double-digit percentage leads in every 3DMark test above two threads and commanding Cinebench wins. The 7840U is the stronger throughput engine for integer math, floating point math, and encryption, and it does all of this inside a mobile envelope while also carrying Radeon 780M graphics, ECC support, and higher memory bandwidth. Identical percentile placement, 77 for both, confirms that in the database's global ranking these two land in the same neighborhood by very different routes.