AMD Ryzen 5 7645HX vs AMD Ryzen 9 3900XT Comparison

The AMD Ryzen 9 3900XT and AMD Ryzen 5 7645HX are two very different processors that land at nearly the same average benchmark score: the 3900XT averages 33,736 points, while the 7645HX averages 33,668 points, a difference of only 0.2%. This near-parity in aggregate scores, however, masks completely opposite performance profiles. The 3900XT, a 12-core desktop part from the 3000 series, dominates heavily threaded workloads, while the 7645HX, a 6-core mobile chip from the 7000 series, wins decisively in single-threaded tests. The data shows that the choice between them depends entirely on whether the workload scales with core count or with per-core efficiency.

Where Each One Wins

The benchmark results split cleanly into two camps. The AMD Ryzen 9 3900XT wins 13 of the 17 head-to-head tests, with its largest advantages coming in multi-threaded and memory-intensive workloads. The AMD Ryzen 5 7645HX wins 4 tests, all of which are single-threaded or lightly threaded. This is a classic core-count versus architecture-efficiency matchup.

The 3900XT pulls ahead in every Cinebench test, both multi-core and single-core. Its lead grows from 22.6% in Cinebench R15 multi-core to 98% in Cinebench R23 multi-core, and it even wins single-core Cinebench tests by 36% to 116.1%. The 7645HX counters in Geekbench, winning single-core by 38.3% and multi-core by 2.2%. In PassMark, the 3900XT takes 10 of 12 tests, with wins ranging from 18.6% in physics to 60% in data encryption, while the 7645HX wins only the single-thread and singlethread tests by 29.8%. The 7645HX's wins are narrow in multi-core (Geekbench) but substantial in single-core, while the 3900XT's wins in multi-core are often massive.

For users running heavily threaded applications like video rendering, 3D modeling, or data compression, the 3900XT is the clear winner. For users whose workloads are mostly single-threaded, such as older games or lightly threaded productivity apps, the 7645HX offers a significant advantage.

Architecture Differences

The two CPUs come from different generations and design philosophies. The 3900XT is built on the Zen 2 architecture with the Matisse 2 codename, manufactured on a 7 nm process at TSMC. It has 12 cores and 24 threads, with a base clock of 3.90 GHz and a boost clock of 4.70 GHz. The 7645HX uses the Zen 4 architecture with the Dragon Range codename, built on a 5 nm process at the same foundry. It has 6 cores and 12 threads, with a base clock of 4.00 GHz and a boost clock of 5.00 GHz.

The process node shrink from 7 nm to 5 nm gives the 7645HX a transistor density advantage, with 6,570 million transistors in a 71 mm² die, versus 7,600 million transistors across a 2x 74 mm² die for the 3900XT. Cache configurations differ substantially: the 3900XT has 64 MB of L3 cache, while the 7645HX has 32 MB of shared L3 cache. The L2 cache also differs, with the 3900XT offering 512 KB per core and the 7645HX offering 1 MB per core.

Memory support is a major differentiator. The 3900XT uses DDR4 with dual-channel memory and 51.2 GB/s bandwidth, while the 7645HX uses DDR5 with dual-channel memory and 83.2 GB/s bandwidth. The 7645HX also supports ECC memory, while the 3900XT does not. PCIe generations differ as well: the 3900XT has Gen 4 with 24 lanes, while the 7645HX has Gen 5 with 28 lanes. The 7645HX includes integrated Radeon 610M graphics, whereas the 3900XT has no integrated graphics. The 3900XT has an unlocked multiplier, while the 7645HX does not. The 3900XT targets the desktop market with an AMD Socket AM4, while the 7645HX targets mobile with an AMD Socket FL1.

FAQ

Q: Which processor has a higher boost clock?

A: The AMD Ryzen 5 7645HX has a boost clock of 5.00 GHz, which is higher than the AMD Ryzen 9 3900XT's boost clock of 4.70 GHz.

Q: Does the AMD Ryzen 5 7645HX have integrated graphics?

A: Yes, the 7645HX includes Radeon 610M integrated graphics. The AMD Ryzen 9 3900XT does not have integrated graphics.

Q: Which CPU offers better single-threaded performance in PassMark?

A: The AMD Ryzen 5 7645HX scores 3,907 in PassMark single-thread, which is 29.8% higher than the 3900XT's score of 2,742.

Q: What is the difference in multi-core Cinebench R23 performance?

A: The 3900XT scores 27,688 in Cinebench R23 multi-core, which is 98% higher than the 7645HX's score of 13,985.

Q: Which processor has a larger L3 cache?

A: The AMD Ryzen 9 3900XT has 64 MB of L3 cache, double the 32 MB of shared L3 cache found on the AMD Ryzen 5 7645HX.

Q: Do both processors support the same memory type?

A: No. The 3900XT supports DDR4 memory, while the 7645HX supports DDR5 memory. The 7645HX also has higher memory bandwidth at 83.2 GB/s versus 51.2 GB/s.

Specification Differences

The two processors differ in almost every major specification category. The 3900XT has 12 cores and 24 threads versus 6 cores and 12 threads for the 7645HX. The 7645HX has a higher base clock (4.00 GHz vs 3.90 GHz) and a higher boost clock (5.00 GHz vs 4.70 GHz). The 3900XT has a much higher TDP at 105 watts versus 45 watts for the 7645HX.

The socket is different: AMD Socket AM4 for the 3900XT and AMD Socket FL1 for the 7645HX. The architecture is Zen 2 versus Zen 4, with codenames Matisse 2 and Dragon Range respectively. The process node is 7 nm for the 3900XT and 5 nm for the 7645HX. Transistor counts are 7,600 million for the 3900XT and 6,570 million for the 7645HX, with die sizes of 2x 74 mm² and 71 mm² respectively.

Cache configurations differ: both have 64 KB L1 per core, but the 3900XT has 512 KB L2 per core versus 1 MB per core on the 7645HX. The 3900XT has 64 MB L3 cache, while the 7645HX has 32 MB shared L3. Memory support is DDR4 for the 3900XT and DDR5 for the 7645HX, with bandwidths of 51.2 GB/s and 83.2 GB/s respectively. ECC memory is supported only on the 7645HX. PCIe is Gen 4 with 24 lanes for the 3900XT, and Gen 5 with 28 lanes for the 7645HX. The 3900XT has no integrated graphics, while the 7645HX has Radeon 610M. The market segment is Desktop for the 3900XT and Mobile for the 7645HX. The 3900XT has an unlocked multiplier with launch MSRP of $499; the 7645HX has a locked multiplier and no launch MSRP listed.

Head-to-Head Benchmarks

The head-to-head data reveals a striking pattern of dominance in opposite directions. The 3900XT wins the Cinebench suite decisively. In Cinebench R15 multi-core, it scores 2,790 against 2,276, a 22.6% advantage. The single-core gap in R15 is even larger at 36%, with scores of 393 versus 289. Moving to Cinebench R23, the 3900XT's multi-core lead expands to 98% (27,688 versus 13,985), and its single-core lead becomes 116.1% (3,909 versus 1,809). These are enormous margins, particularly in single-core where the newer architecture was expected to excel.

The 7645HX fights back in Geekbench. It wins single-core with a score of 2,657 versus 1,640, a 38.3% advantage. It also wins multi-core, but narrowly, scoring 11,586 versus 11,329, a 2.2% lead. This suggests that the 7645HX's higher clock speeds and newer architecture close the multi-core gap despite having half the cores, but cannot overcome the 3900XT's raw thread count in Cinebench.

In PassMark, the 3900XT dominates most tests. Data compression shows a 49.7% lead (452,328 versus 302,256). Data encryption is even more lopsided at 60% (28,634 versus 17,900). Extended instructions favor the 3900XT by 24.5% (28,586 versus 22,969). Find prime numbers gives a 20.2% win (214 versus 178). Floating point math is a 19.9% advantage (58,513 versus 48,798). Integer math is 28.8% ahead (99,722 versus 77,432). Multithread shows a 23% lead (32,575 versus 26,476). Physics is 18.6% higher (1,776 versus 1,497). Random string sorting is 40.3% ahead (48,327 versus 34,434). The only PassMark wins for the 7645HX are in single-thread tests, where it scores 3,907 versus 2,742, a 29.8% advantage in both single_thread and singlethread results.

The Verdict

The benchmark data supports a clear split recommendation. For users building a desktop workstation where multi-threaded performance is critical, the AMD Ryzen 9 3900XT is the superior choice. It wins 13 of 17 tests, with particularly strong showings in Cinebench multi-core (98% lead in R23) and PassMark data compression (49.7% lead). Its 12 cores and 24 threads, combined with 64 MB of L3 cache, provide substantial advantages in rendering, compression, and encryption workloads.

The AMD Ryzen 5 7645HX is the better option for single-threaded performance and mobile use cases. It wins Geekbench single-core by 38.3% and PassMark single-thread by 29.8%, demonstrating the benefit of its Zen 4 architecture, 5.00 GHz boost clock, and DDR5 memory support. Its 45-watt TDP and integrated Radeon 610M graphics make it suitable for laptops, where the 3900XT's 105-watt TDP and lack of integrated graphics would be problematic.

The near-identical average benchmark scores (0.2% apart) and matching 84th percentile rankings among all CPUs make this a balanced comparison. The deciding factor is workload type: thread-heavy applications favor the 3900XT, while clock-sensitive, single-threaded tasks favor the 7645HX. The 3900XT's launch MSRP of $499 reflects its desktop positioning and higher core count, while the 7645HX's lack of a listed launch MSRP aligns with its mobile market segment. Both processors are active in production, so availability is not a differentiator. The data does not indicate a universal winner; it indicates two specialized tools for different jobs.