AMD Ryzen 9 3900 vs AMD Ryzen 9 7845HX Comparison

The AMD Ryzen 9 7845HX and the AMD Ryzen 9 3900 are both 12-core, 24-thread processors, yet they are separated by a generation gap that produces one of the most decisive benchmark sweeps in the database. The 7845HX wins all 17 head-to-head tests, with margins ranging from 23% to over 66%. The 3900, a desktop part from the Zen 2 era, remains a capable performer in its own right, but the data indicates it is thoroughly outclassed by the mobile Zen 4 chip. Their average benchmark scores are nearly identical — 44141 for the 7845HX versus 44039 for the 3900, a 0.2% difference — but this aggregate figure masks the fact that the 3900’s score is buoyed by its inclusion in the same performance tier, not by matching the newer chip’s per-thread efficiency. Both processors sit at the 92nd percentile among all CPUs, yet the 7845HX achieves this standing with a dramatically newer architecture and a much lower power envelope.

FAQ

Q: How does the AMD Ryzen 9 7845HX compare to the AMD Ryzen 9 3900 in multi-threaded workloads?

A: The 7845HX dominates, leading by 47.1% in Cinebench R23 multi-core (38232 vs 25988) and by 47.2% in PassMark’s multithread test (45010 vs 30586). This consistent 47% advantage appears across all Cinebench versions.

Q: Which processor offers better single-core performance?

A: The 7845HX wins decisively, with a 47.1% lead in Cinebench R23 single-core (5397 vs 3669) and a 51.1% advantage in PassMark single-thread (3935 vs 2604). The gap is uniform across all single-threaded tests.

Q: Are the two processors from the same architecture generation?

A: No. The 7845HX uses Zen 4 architecture on a 5 nm TSMC process, while the 3900 uses Zen 2 on a 7 nm TSMC process. This architectural difference is the primary driver of the performance disparity.

Q: What are the memory and platform differences?

A: The 7845HX supports DDR5 memory with dual-channel bandwidth of 83.2 GB/s, while the 3900 uses DDR4 with 51.2 GB/s bandwidth. The 7845HX also supports ECC memory and PCIe Gen 5, whereas the 3900 lacks ECC support and uses PCIe Gen 4.

Q: Does the 7845HX have integrated graphics?

A: Yes, the 7845HX includes a Radeon 610M iGPU. The 3900 has no integrated graphics, requiring a discrete GPU for display output.

Q: Which processor has the higher boost clock?

A: The 7845HX boosts to 5.20 GHz, while the 3900 peaks at 4.30 GHz. The 7845HX also has a lower base clock of 3.00 GHz versus the 3900’s 3.10 GHz.

Where Each One Wins

The benchmark results are categorical: the AMD Ryzen 9 7845HX wins every single head-to-head test, leaving the AMD Ryzen 9 3900 without a single victory across 17 comparisons. There is no workload category where the 3900 manages to claw back a lead, making this a one-sided contest. The 7845HX’s smallest margin is 23% in PassMark data encryption (32789 vs 26657), while its largest is 66.2% in PassMark floating point math (94287 vs 56730). Even in tests that typically favor older architectures due to lower memory latency requirements, such as integer math and prime number finding, the Zen 4 chip prevails by 58.8% and 62.1%, respectively.

For the 3900, the only conceivable “win” is contextual rather than performance-based. It is a desktop AM4 processor with a 65 W TDP, which in a desktop chassis allows for simpler cooling solutions compared to the 7845HX’s mobile FL1 socket. However, this is not a benchmark advantage. The data shows the 7845HX achieves its results while being a mobile part, meaning it delivers superior performance in a form factor that the 3900 cannot match. The 3900’s production status remains active, but its performance class has been entirely superseded by the newer Dragon Range chip.

Architecture Differences

The two processors represent distinct generations of AMD’s core designs. The 7845HX is built on Zen 4, codenamed Dragon Range, and fabricated on a 5 nm TSMC process with 13,140 million transistors spread across a dual-die configuration of 2x 71 mm². The 3900 uses Zen 2, codenamed Matisse, on a 7 nm TSMC process with 7,600 million transistors across 2x 74 mm² dies. This process shrink and transistor density increase is fundamental to the 7845HX’s performance advantage.

Cache hierarchies differ significantly. Both have 64 MB of L3 cache, but the L2 cache differs: the 7845HX has 1 MB per core, while the 3900 has 512 KB per core. L1 cache is identical at 64 KB per core. This doubled L2 capacity on the newer chip reduces latency for frequently accessed data, contributing to its superior single-threaded scores.

Memory architecture is another major divergence. The 7845HX supports DDR5 with a dual-channel bus delivering 83.2 GB/s bandwidth, while the 3900 is limited to DDR4 at 51.2 GB/s. The 7845HX also supports ECC memory, a feature absent on the 3900. PCIe connectivity differs as well: the 7845HX offers Gen 5 with 28 CPU lanes, while the 3900 provides Gen 4 with 24 lanes. The 7845HX integrates a Radeon 610M GPU, whereas the 3900 has no integrated graphics.

The transistor count difference is stark — 13,140 million versus 7,600 million — reflecting the density improvements of the 5 nm node. The die sizes are nearly identical (71 mm² vs 74 mm² per die), meaning the 7845HX packs nearly twice the transistors into a slightly smaller area. This is the physical basis for its higher clock speeds and greater instruction-level parallelism.

Specification Differences

The most immediate difference is clock speed. The 7845HX has a base clock of 3.00 GHz and a boost clock of 5.20 GHz, while the 3900 operates at 3.10 GHz base and 4.30 GHz boost. Despite a lower base clock, the 7845HX’s boost is 0.9 GHz higher, enabling its single-threaded dominance.

Power and platform targets diverge sharply. The 7845HX is a mobile processor with a 55 W TDP on the AMD Socket FL1, designed for high-performance laptops. The 3900 is a desktop part with a 65 W TDP on the AMD Socket AM4. This means the 7845HX delivers significantly more performance at a lower thermal design power, proof of the efficiency gains of Zen 4.

Memory support is exclusive per platform: DDR5 for the 7845HX versus DDR4 for the 3900. The 7845HX also has higher memory bandwidth (83.2 GB/s vs 51.2 GB/s) and ECC support. PCIe generation and lane counts differ (Gen 5, 28 lanes vs Gen 4, 24 lanes). The 7845HX includes integrated Radeon 610M graphics; the 3900 has none. Release dates are also far apart: January 2023 for the 7845HX versus September 2019 for the 3900.

The 3900 has a launch MSRP of $499, which can be stated once as historical reference. Both processors have unlocked multipliers, allowing overclocking, and both remain in active production. Their part numbers are 100-000000871 for the 7845HX and 100-000000070 for the 3900.

Head-to-Head Benchmarks

The Cinebench suite shows a remarkably uniform 47.1% to 47.2% advantage for the 7845HX across all versions and thread counts. In Cinebench R15 multi-core, the 7845HX scores 3853 versus the 3900’s 2619, a 47.1% lead. The single-core R15 result is 543 versus 369, a 47.2% margin. This consistency extends to R20 (16057 vs 10914 multi, 2266 vs 1540 single) and R23 (38232 vs 25988 multi, 5397 vs 3669 single). The identical percentage deltas suggest a fixed architectural efficiency advantage that scales linearly with frequency and IPC improvements.

PassMark tests reveal the largest margins. Floating point math shows the biggest gap at 66.2% (94287 vs 56730), indicating the Zen 4’s superior FPU throughput. Integer math follows closely at 58.8% (155118 vs 97698). Extended instructions show a 57.3% lead (41020 vs 26073), and prime number finding is 62.1% higher (329 vs 203). These results point to deeper execution resources and better instruction scheduling in the newer architecture.

The 7845HX’s smallest win is in data encryption at 23% (32789 vs 26657), suggesting that cryptographic workloads are less dependent on raw core speed and more on memory bandwidth, where the DDR5 advantage still yields a solid but smaller gain. Data compression shows a 31.3% lead (543539 vs 413887), while random string sorting is 40.8% faster (63223 vs 44902). Physics simulation in PassMark shows a 45.1% advantage (2346 vs 1617).

Single-threaded PassMark results show a 51.1% lead (3935 vs 2604), which is slightly higher than the Cinebench single-core deltas. This indicates that the 7845HX’s boost clock advantage is more pronounced in certain instruction mixes. Overall, the head-to-head data leaves no ambiguity: the 7845HX is faster in every measurable dimension, with margins that range from roughly one-quarter to two-thirds better than the 3900.