AMD Ryzen 9 3900X vs AMD Ryzen 9 7845HX Comparison

The AMD Ryzen 9 7845HX and the AMD Ryzen 9 3900X share a name, core count, and thread count, but the benchmark data reveals they are entirely different classes of performance. The 7845HX wins every single head-to-head benchmark in the database, with 17 wins against 0 for the 3900X. The average benchmark scores are nearly identical — 46654 for the 7845HX and 46487 for the 3900X — placing both at the 89th percentile among all CPUs. However, that parity in average score masks a consistent and often massive performance gap in specific workloads. The 7845HX is a mobile processor with a 55W TDP, while the 3900X is a desktop part with a 105W TDP, yet the newer architecture wins in every measured category, from single-thread to multi-thread tasks.

The Verdict

The data directs a clear split: the 7845HX is the superior processor for almost any workload measured, while the 3900X’s only remaining strength is its platform’s maturity and memory support. The 7845HX beats the 3900X by 41.5% in Cinebench R23 multi-core and by 35.2% in single-core. In Geekbench, the lead is 39.2% multi-core and 43.6% single-core. These are not marginal gains; they represent a generational leap in efficiency and per-clock performance. The 7845HX achieves these results with a 55W TDP, compared to the 3900X’s 105W TDP. For a mobile laptop user, the 7845HX offers desktop-class performance in a power envelope that the 3900X cannot match.

The 3900X retains one distinct advantage: it supports DDR4 memory, which is a mature and widely available standard. The 7845HX requires DDR5. If you are building a new desktop system with existing DDR4 memory and want to avoid a platform transition, the 3900X remains a viable, still-active option. However, for any new purchase, the benchmark data overwhelmingly favors the 7845HX. The 3900X is also the only one with a launch MSRP of $499, but that price point does not compensate for the 30-60% performance deficits across the board. The 7845HX is the pick for raw performance, especially in single-threaded and floating-point workloads, while the 3900X is only sensible for a DDR4-specific build where the architecture’s weaknesses are acceptable.

Architecture Differences

The two chips are built on fundamentally different foundations. The 7845HX uses AMD’s Zen 4 architecture, codenamed Dragon Range, manufactured on a 5 nm process by TSMC. The 3900X uses Zen 2, codenamed Matisse, on a 7 nm process. The process node shrink is a major factor in the 7845HX’s ability to deliver more performance at less than half the TDP. The 7845HX packs 13,140 million transistors across two 71 mm² dies, while the 3900X has 7,600 million transistors across two 74 mm² dies. The newer chip fits nearly double the transistors into a slightly smaller total die area.

Cache configurations also differ significantly. Both have 64 MB of L3 cache, but the 7845HX allocates 1 MB of L2 cache per core, while the 3900X has only 512 KB per core. The L1 cache is identical at 64 KB per core. Memory support diverges completely: the 7845HX uses DDR5 with a dual-channel bus and 83.2 GB/s bandwidth, while the 3900X uses DDR4 with 51.2 GB/s bandwidth. The 7845HX also supports ECC memory, while the 3900X does not. The 7845HX features integrated graphics (Radeon 610M) and a newer PCIe Gen 5 interface with 28 lanes, whereas the 3900X has no integrated graphics and offers PCIe Gen 4 with 24 lanes. The 7845HX is unlocked, as is the 3900X, but the mobile part’s socket (AMD Socket FL1) is not interchangeable with the desktop AM4 socket.

FAQ

Q: Which processor is faster in multi-threaded workloads?

A: The 7845HX is consistently faster. It scores 26876 in Cinebench R23 multi-core versus 19000 for the 3900X, a 41.5% advantage. In Geekbench multi-core, the 7845HX leads with 16633 to 11948, a 39.2% gap. PassMark multi-thread shows 45010 for the 7845HX and 32544 for the 3900X, a 38.3% lead.

Q: Is the single-core performance difference as large as the multi-core gap?

A: Yes, and sometimes larger. The 7845HX wins Cinebench R23 single-core by 35.2% (1852 vs 1370) and Geekbench single-core by 43.6% (2389 vs 1664). PassMark single-thread shows a 45.6% lead for the 7845HX (3935 vs 2703).

Q: Can the 3900X beat the 7845HX in any benchmark?

A: No. In the 17 head-to-head benchmarks recorded, the 7845HX wins all of them. The closest margin is in PassMark data encryption, where the 7845HX leads by 14.7% (32789 vs 28586).

Q: What is the biggest performance gap between the two?

A: The largest delta is in PassMark floating-point math, where the 7845HX scores 94287 against 58434 for the 3900X, a 61.4% advantage. The next largest is PassMark integer math at 55.7% (155118 vs 99628).

Q: Do they have the same core and thread counts?

A: Yes, both have 12 cores and 24 threads. However, the 7845HX has a higher boost clock of 5.20 GHz versus 4.60 GHz for the 3900X, and a lower base clock of 3.00 GHz versus 3.80 GHz.

Q: Which processor supports DDR5 memory?

A: Only the 7845HX supports DDR5. The 3900X is limited to DDR4. The 7845HX also offers higher memory bandwidth at 83.2 GB/s versus 51.2 GB/s for the 3900X.

Specification Differences

The two processors differ in nearly every specification except core count and L3 cache size. The 7845HX has a base clock of 3.00 GHz and a boost clock of 5.20 GHz, while the 3900X runs at 3.80 GHz base and 4.60 GHz boost. The 7845HX’s TDP is 55W, less than half of the 3900X’s 105W. The socket changes from AMD Socket FL1 (mobile) to AMD Socket AM4 (desktop). The process node is 5 nm for the 7845HX and 7 nm for the 3900X. Transistor count is 13,140 million versus 7,600 million, with die sizes of 2x 71 mm² and 2x 74 mm² respectively. L2 cache per core is 1 MB on the 7845HX and 512 KB on the 3900X. Memory support is DDR5 versus DDR4, with bandwidth of 83.2 GB/s versus 51.2 GB/s. ECC memory is supported only on the 7845HX. PCIe generation and lanes differ: Gen 5 with 28 lanes on the 7845HX, Gen 4 with 24 lanes on the 3900X. The 7845HX includes Radeon 610M integrated graphics; the 3900X has none. The market segment is Mobile for the 7845HX and Desktop for the 3900X. The 7845HX was released in January 2023, while the 3900X launched in July 2019.

Head-to-Head Benchmarks

The 7845HX dominates every benchmark, but the margins vary significantly by workload. The largest win is in PassMark floating-point math, where the 7845HX scores 94287 against 58434 for the 3900X, a 61.4% advantage. This suggests a substantial improvement in FPU throughput per clock, likely due to the Zen 4 architecture. The second-largest gap is in PassMark integer math, with the 7845HX at 155118 versus 99628, a 55.7% lead. In PassMark find prime numbers, the 7845HX wins by 53.7% (329 vs 214), indicating faster integer calculation rates.

Single-threaded performance shows a consistent 35-45% lead. Geekbench single-core has the 7845HX at 2389 versus 1664 for the 3900X, a 43.6% gap. PassMark single-thread shows 3935 versus 2703, a 45.6% lead. Cinebench R23 single-core is 1852 versus 1370, a 35.2% gap. These numbers indicate that the 7845HX is not just a multi-core monster; its per-core performance is vastly superior.

Multi-threaded benchmarks show similar patterns. Cinebench R23 multi-core is 26876 for the 7845HX and 19000 for the 3900X, a 41.5% lead. Geekbench multi-core shows 16633 versus 11948, a 39.2% gap. PassMark multi-thread is 45010 versus 32544, a 38.3% lead. The smallest win comes in PassMark data encryption, where the 7845HX scores 32789 against 28586, a 14.7% advantage. This indicates that encryption workloads rely on features that are less improved between Zen 2 and Zen 4. In PassMark data compression, the 7845HX leads by 21.1% (543539 vs 448906), and in extended instructions, it wins by 40.4% (41020 vs 29221).

Where Each One Wins

The 7845HX wins in every measured category, but the magnitude of its wins varies. For users who prioritize floating-point math, such as scientific computing or 3D rendering, the 7845HX is the clear choice — its 61.4% lead in floating-point math is the largest single advantage in the dataset. For integer-heavy workloads like data processing or general productivity, the 7845HX also excels, with a 55.7% lead in integer math and a 53.7% lead in prime number calculation. Single-threaded applications, which often include older software or games that rely on one core, will see a 35-45% improvement with the 7845HX, making it the better option for responsiveness.

The 3900X’s only practical advantage is platform compatibility. It uses the AM4 socket and supports DDR4 memory, which means users with existing DDR4 modules or AM4 motherboards can upgrade or build without replacing those components. The 3900X also has a launch MSRP of $499, but that is a historical figure. For any new build where memory and motherboard are being purchased fresh, the 7845HX’s performance advantages — including a 30.8% lead in PassMark physics and a 30.9% lead in random string sorting — make it the superior choice. However, the 7845HX is a mobile part, so it is only available in laptops or systems designed for the FL1 socket. The 3900X, as a desktop chip, is the only option for a standard AM4 desktop build, but the benchmark data shows it is significantly slower in every workload tested.