Intel Core i3-1215U vs Intel Core i5-8400 Comparison

The Intel Core i5-8400 and Intel Core i3-1215U represent two distinct design philosophies from Intel: a desktop-focused, fixed-clock Coffee Lake part from 2017 versus a mobile-oriented, hybrid Alder Lake-U processor from 2022. The data shows a split decision: the i5-8400 dominates in render workloads and most CPU-bound tasks, while the i3-1215U counters with superior single-threaded throughput, memory encryption, and integer math. The i5-8400 secures 12 benchmark wins against 7 for the i3-1215U, yet the overall average benchmark scores are nearly identical (12765 vs 12604, a 1.3% gap). This suggests the choice hinges entirely on workload and platform constraints rather than raw aggregate performance.

FAQ

Q: Which processor has the higher multi-core render score in Cinebench R23?

A: The Intel Core i5-8400 leads with a Cinebench R23 multi-core score of 7847, compared to 6644 for the i3-1215U, a difference of 18.1% in favor of the desktop chip.

Q: Does the mobile i3-1215U ever beat the i5-8400 in single-threaded tests?

A: Yes. The i3-1215U wins Geekbench single-core (1485 vs 1353, an 8.9% advantage) and Passmark single-thread (3218 vs 2371, a 26.3% advantage), driven by its higher boost clock of 4.40 GHz versus 4.00 GHz.

Q: What is the biggest performance gap in either direction?

A: The largest margin is in Passmark data encryption, where the i3-1215U scores 7041 against 2824 for the i5-8400, a 59.9% swing. Conversely, the i5-8400’s biggest win is Passmark extended instructions at 11543 vs 6868, a 68.1% advantage.

Q: How do their core and thread counts compare?

A: Both have 6 physical cores, but the i3-1215U supports 8 threads via hyper-threading, while the i5-8400 has 6 threads. The i3-1215U also uses a hybrid architecture with a base clock of 1200.00 MHz and a boost of 4.40 GHz; the i5-8400 runs at 2.80 GHz base and 4.00 GHz boost.

Q: Are these processors on the same socket?

A: No. The i5-8400 uses Intel Socket 1151, while the i3-1215U uses Intel BGA 1744, making them incompatible with each other’s motherboards.

Q: Which chip has better memory bandwidth support?

A: The i5-8400 lists a memory bandwidth of 42.7 GB/s with DDR4 support. The i3-1215U supports both DDR4 and DDR5, but its memory bandwidth figure is not provided in the data.

Architecture Differences

The architectural divide between these two chips is stark. The i5-8400 is built on the Coffee Lake architecture using a 14 nm process, while the i3-1215U uses the Alder Lake-U architecture on a 10 nm node. This process shrink allows the mobile chip to integrate more cache per core: the i3-1215U has 80 KB of L1 and 1.25 MB of L2 per core, versus 64 KB L1 and 256 KB L2 per core for the i5-8400. Total L3 cache also favors the newer chip, with 10 MB shared versus 9 MB shared on the i5-8400.

The i3-1215U’s hybrid design explains its unusual base clock of 1200.00 MHz, which is far lower than the i5-8400’s 2.80 GHz. Despite that low base, its boost reaches 4.40 GHz, exceeding the i5-8400’s 4.00 GHz. The mobile part also has a 15 W TDP against 65 W for the desktop chip, reflecting its BGA 1744 socket and Mobile market segment. The i5-8400 is marked End-of-life and released in 2017-10-04, while the i3-1215U is Active and released in 2022-02-22.

PCIe support differs too: the i5-8400 provides Gen 3 with 16 lanes (CPU only), whereas the i3-1215U offers Gen 4 with 20 lanes (CPU only). Integrated graphics also diverge: the i5-8400 has UHD Graphics 630, while the i3-1215U has UHD Graphics 64EU. Neither chip supports ECC memory, and both are dual-channel, but the i3-1215U expands memory compatibility to include DDR5 alongside DDR4, while the i5-8400 is limited to DDR4. The i5-8400 has a known die size of 154 mm²; the die size for the i3-1215U is not listed.

Head-to-Head Benchmarks

The i5-8400 wins every Cinebench iteration, and the margin is consistent. In Cinebench R15, R20, and R23, both multi-core and single-core tests show an 18.1% lead for the i5-8400, with the sole exception of R23 single-core at 18.0%. For example, Cinebench R23 multi-core scores are 7847 for the i5-8400 against 6644 for the i3-1215U. This uniformity suggests that the i5-8400’s higher sustained clocks and desktop power envelope provide a stable advantage in render tests, despite the i3-1215U’s newer core design.

Geekbench results split the field. The i5-8400 wins multi-core with 5088 versus 4365, a 16.6% margin. However, the i3-1215U takes single-core at 1485 versus 1353, an 8.9% gain. This pattern repeats in Passmark tests: the i5-8400 wins data compression (129951 vs 116705, 11.3% ahead), extended instructions (11543 vs 6868, 68.1% ahead), find prime numbers (37 vs 32, 15.6% ahead), physics (635 vs 583, 8.9% ahead), and random string sorting (15952 vs 13046, 22.3% ahead).

The i3-1215U counters with decisive wins in data encryption (7041 vs 2824, 59.9% ahead), integer math (35534 vs 25573, 28% ahead), floating-point math (25379 vs 22006, 13.3% ahead), and multithread (10472 vs 9225, 11.9% ahead). The single-thread Passmark score also favors the i3-1215U by 26.3% (3218 vs 2371). Notably, the i3-1215U’s multithread win in Passmark contrasts with its loss in Geekbench multi-core, indicating that the benchmark’s specific instruction mix favors the mobile chip’s higher thread count and newer instruction set extensions.

Specification Differences

The key specification differences between the two parts are substantial. The i5-8400 has 6 cores and 6 threads, while the i3-1215U has 6 cores and 8 threads. Base clocks are wildly different: 2.80 GHz for the i5-8400 versus 1200.00 MHz for the i3-1215U. Boost clocks reverse the order, with the i3-1215U at 4.40 GHz and the i5-8400 at 4.00 GHz. TDP is another major divider: 65 W for the desktop chip versus 15 W for the mobile chip.

Sockets are incompatible: Intel Socket 1151 for the i5-8400, Intel BGA 1744 for the i3-1215U. Process nodes differ (14 nm vs 10 nm), as do cache hierarchies (L1: 64 KB vs 80 KB per core; L2: 256 KB vs 1.25 MB per core; L3: 9 MB vs 10 MB shared). Memory support diverges: DDR4 only for the i5-8400, DDR4 and DDR5 for the i3-1215U. The i5-8400 has a listed memory bandwidth of 42.7 GB/s; the i3-1215U has no bandwidth figure. PCIe generations and lane counts differ (Gen 3, 16 lanes vs Gen 4, 20 lanes). Integrated graphics are UHD Graphics 630 versus UHD Graphics 64EU. The i5-8400 has a launch MSRP of $182; the i3-1215U has no listed launch MSRP. Production status: End-of-life versus Active. Release dates: 2017-10-04 versus 2022-02-22. The i5-8400 has a die size of 154 mm²; the i3-1215U’s die size is not provided.

Where Each One Wins

The i5-8400 wins in scenarios that demand consistent multi-core rendering and compression. Its Cinebench R23 multi-core score of 7847 is 18.1% higher, making it the stronger choice for CPU-based 3D rendering or video encoding workloads that scale across cores. It also leads in data compression (129951 vs 116705) and random string sorting (15952 vs 13046), suggesting an edge in file archiving and database-style operations. The 68.1% lead in extended instructions points to superior performance in workloads leveraging advanced SIMD or specialized instruction sets, such as certain scientific or financial computations.

The i3-1215U wins where single-thread responsiveness and modern instruction efficiency matter. Its Passmark single-thread score of 3218 is 26.3% higher, which translates to snappier application launches and better performance in lightly-threaded tasks. The 59.9% margin in data encryption indicates a strong advantage in security-related operations, such as VPN encryption or disk encryption. Integer math (35534 vs 25573) and floating-point math (25379 vs 22006) wins suggest the mobile chip handles arithmetic-heavy code more efficiently, despite its lower base clock. The multithread win in Passmark (10472 vs 9225) shows that its 8 threads can outpace the 6-thread desktop chip in certain parallel workloads, likely due to the newer architecture’s higher per-core throughput.

The Verdict

The data supports a clear split. Pick the Intel Core i5-8400 if the workload is dominated by multi-threaded rendering, compression, or extended-instruction processing. Its consistent 18.1% lead across all Cinebench tests and its 68.1% advantage in extended instructions make it the superior choice for professional content creation or batch processing tasks. The i5-8400 also holds a 16.6% edge in Geekbench multi-core, reinforcing its strength in general multi-threaded productivity. Its higher TDP and desktop socket suggest it belongs in a system where power draw is not a constraint.

Choose the Intel Core i3-1215U for systems prioritizing single-threaded speed, encryption, or arithmetic throughput, particularly where mobility and low power are essential. The 26.3% single-thread win and 59.9% encryption advantage are decisive for interactive applications and security workloads. Its 8 threads and 10 MB L3 cache help it win Passmark multithread by 11.9%, even while losing other multi-core tests. The i3-1215U’s Active production status and 10 nm process also indicate a longer-term platform relevance, but the benchmark data alone shows that the i5-8400 remains competitive in raw compute despite being End-of-life. The final call rests on whether the workload favors the i5-8400’s render and compression strengths or the i3-1215U’s single-thread and encryption capabilities.