Intel Core i5-9400T vs Intel Core i7-8559U Comparison

FAQ

Q: Which processor has the higher boost clock?

A: The Intel Core i7-8559U boosts to 4.50 GHz, while the Intel Core i5-9400T tops out at 3.40 GHz. The i7-8559U also has a much higher base clock of 2.70 GHz compared to the i5-9400T's 1800.00 MHz.

Q: How many cores and threads does each CPU offer?

A: The Core i7-8559U has 4 cores and 8 threads, whereas the Core i5-9400T has 6 cores and 6 threads. That means the i7 has hyper-threading, while the i5 relies on its higher physical core count for multi-threaded work.

Q: Which processor won the most benchmarks in the direct comparison?

A: The Core i7-8559U won all 8 recorded head-to-head tests. Its largest victory came in Geekbench single-core, where it led by 20.1 percent.

Q: What is the difference in integrated graphics?

A: The Core i7-8559U integrates Iris Pro Plus graphics, while the Core i5-9400T uses UHD 630. Both are Intel solutions, but the mobile chip carries the higher-tier graphics brand.

Q: How do the two CPUs rank among all processors in the database?

A: Both sit at the 47th percentile versus all CPUs. The Core i7-8559U has an average benchmark score of 2225, compared to 2136 for the Core i5-9400T.

Q: Are both processors still in production?

A: No. The Core i7-8559U is listed as Active, while the Core i5-9400T is marked as End-of-life. The i7-8559U is a mobile part, and the i5-9400T is a desktop part.

Architecture Differences

The two processors come from different Intel generations and target different market segments. The Core i7-8559U is a Kaby Lake-R mobile chip built on the Kaby Lake architecture, while the Core i5-9400T is a Coffee Lake desktop part. Both use Intel's 14 nm process node and are manufactured by Intel, but their underlying designs diverge in core count, packaging, and platform features.

The i7-8559U is a 4-core, 8-thread processor with hyper-threading enabled. It uses the Intel BGA 1356 socket, which is a soldered mobile package. The i5-9400T is a 6-core, 6-thread processor without hyper-threading, and it fits into the standard Intel Socket 1151 desktop platform. This is a fundamental difference: the i7 relies on simultaneous multithreading to fill execution slots, while the i5 depends entirely on its two extra physical cores.

Cache layouts also differ. Both chips have 64 KB of L1 cache per core and 256 KB of L2 cache per core, but the shared L3 cache is 8 MB on the i7-8559U and 9 MB on the i5-9400T. The extra 1 MB of L3 on the i5 is a modest advantage, though the i7's higher clock speeds help offset it in most workloads.

The market positioning is clear from the sockets and integrated graphics. The i7-8559U is a mobile part with Iris Pro Plus graphics, designed for compact notebooks and ultraportables. The i5-9400T is a desktop processor with UHD 630 graphics and a 35 W TDP, aimed at low-power desktop builds. The i7-8559U carries a 28 W TDP despite the mobile form factor, which is a high thermal envelope for its class.

Memory support is DDR4 for both, but the database records additional details for the i5-9400T: dual-channel memory and 42.7 GB/s of memory bandwidth. The i5 also lists PCIe Gen 3 with 16 lanes from the CPU. The i7-8559U has no recorded PCIe or memory bandwidth data, so direct comparisons in those areas are not possible from the recorded measurements.

Head-to-Head Benchmarks

The direct comparison between these two processors is remarkably one-sided. The Core i7-8559U won all 8 head-to-head tests, but the margins vary significantly by workload type. The Cinebench suite shows close results, while Geekbench reveals a decisive single-core gap.

Starting with Cinebench R15 multi-core, the i7-8559U scores 703 against 695 for the i5-9400T, a 1.2 percent lead. The single-core R15 result is 99 versus 97, a 2.1 percent margin. These are small differences, essentially within the range of run-to-run variation, but the i7 wins both.

Cinebench R20 follows the same pattern. Multi-core is 2933 for the i7 against 2896 for the i5, a 1.3 percent lead. Single-core is 414 versus 408, a 1.5 percent edge. Cinebench R23 repeats the trend: multi-core 6984 versus 6896 (1.3 percent), single-core 986 versus 973 (1.3 percent). The consistency across R15, R20, and R23 suggests that the i7's clock advantage translates into a steady, if modest, performance lead in rendering workloads.

The Geekbench results tell a different story. In Geekbench multi-core, the i7-8559U scores 4293 against 3969 for the i5-9400T, an 8.2 percent advantage. That is a substantial margin, likely reflecting the combination of the i7's high boost clock and hyper-threading in integer and floating-point tasks. The single-core Geekbench test is even more lopsided: 1384 versus 1152, a 20.1 percent lead for the i7. This is the largest delta in the entire comparison and signals that the i7-8559U has a clear per-thread performance advantage.

The overall benchmark averages confirm the trend. The i7-8559U has an average benchmark score of 2225, while the i5-9400T averages 2136. Both CPUs sit at the 47th percentile against all processors in the database, which places them in the same broad performance tier, but the i7 is ahead in every recorded metric.

Specification Differences

The two processors differ in several key specification fields. The core and thread counts are the most obvious divergence: the i7-8559U offers 4 cores and 8 threads, while the i5-9400T offers 6 cores and 6 threads. The i7 has hyper-threading, the i5 does not.

Clock speeds are drastically different. The i7-8559U has a base clock of 2.70 GHz and a boost clock of 4.50 GHz. The i5-9400T has a base clock of 1800.00 MHz and a boost clock of 3.40 GHz. The i7's boost clock is 1.10 GHz higher, and its base clock is nearly 1 GHz higher as well.

Thermal design power also differs, with the i7-8559U rated at 28 W and the i5-9400T at 35 W. This is notable because the i7 achieves higher performance while consuming less rated power, though the two parts serve different platforms.

The sockets are incompatible: the i7-8559U uses Intel BGA 1356, a soldered mobile socket, while the i5-9400T uses Intel Socket 1151 for desktop boards. The architecture names differ as well, Kaby Lake-R versus Coffee Lake, and the generations are listed as Core i7 (Kaby Lake-U Refresh) versus Core i5 (Coffee Lake Refresh).

Cache amounts differ in L3 only: 8 MB shared on the i7 versus 9 MB shared on the i5. L1 and L2 are identical at 64 KB and 256 KB per core respectively. The die size is recorded as 123 mm² for the i7-8559U, with no die size data for the i5-9400T.

Integrated graphics differ: Iris Pro Plus on the i7-8559U versus UHD 630 on the i5-9400T. The i5-9400T has additional recorded memory and PCIe details, including dual-channel memory, 42.7 GB/s memory bandwidth, and PCIe Gen 3 with 16 lanes from the CPU. These fields are not recorded for the i7-8559U.

Production status separates the two as well. The i7-8559U is Active, while the i5-9400T is End-of-life. The i7-8559U released on 2018-04-04, and the i5-9400T followed on 2018-08-31. Neither processor has a recorded launch MSRP in the database. Both are multiplier-unlocked false, meaning neither supports unlocked overclocking.

Where Each One Wins

The Core i7-8559U wins in every recorded benchmark, so the use-case split is largely about the magnitude of its advantages rather than which chip is faster overall. The i7 is the stronger choice for single-threaded performance, as shown by the 20.1 percent lead in Geekbench single-core. Applications that rely on high per-core speed, such as older games, lightly threaded productivity tools, or responsive system interaction, favor the i7 decisively.

The i7-8559U also leads in multi-threaded rendering, but by a much smaller margin. Its Cinebench R23 multi-core score of 6984 is only 1.3 percent ahead of the i5-9400T's 6896. The i5's two extra physical cores help it close the gap against the i7's hyper-threading and clock advantage. For sustained all-core workloads, the i5-9400T is nearly a match, but it still loses in every recorded test.

The Geekbench multi-core result of 8.2 percent in favor of the i7 suggests that the i7's advantage extends beyond rendering into other multi-threaded workloads. The i7's combination of 8 threads and a 4.50 GHz boost clock appears to be more effective than the i5's 6 physical cores at 3.40 GHz in these tests.

For desktop builders, the i5-9400T has the advantage of a standard Socket 1151 platform, dual-channel memory support, and 42.7 GB/s of memory bandwidth. It also has a larger shared L3 cache at 9 MB. The i5-9400T is a viable pick for low-power desktop systems where the 35 W TDP and standard socket matter more than peak per-thread performance.

For mobile users, the i7-8559U is the clear winner. It delivers higher scores across the board while fitting into a BGA 1356 package with a 28 W TDP. The Iris Pro Plus graphics also give it a stronger integrated GPU option on paper, which matters for compact systems without a discrete graphics card.

The production status difference is worth noting for system builders. The i7-8559U remains Active, while the i5-9400T is End-of-life. For new designs, the i7-8559U is the more future-proof choice from an availability standpoint. The i5-9400T may still appear in existing desktop inventory, but its end-of-life status limits its appeal for new builds.

In summary, the i7-8559U wins all performance comparisons and is the better chip for single-threaded tasks, mobile deployments, and any workload where its 20.1 percent Geekbench single-core advantage matters. The i5-9400T is competitive in multi-core rendering, coming within 1.3 percent in Cinebench R23, and offers desktop platform benefits like Socket 1151 and dual-channel memory, but it trails in every recorded benchmark.