CPU Comparison

Head-to-Head Benchmarks

The benchmark data presents an unusually one-sided picture: the Intel Xeon E5645 wins all six head-to-head Cinebench comparisons against the Intel Core i3-8121U. The margin is remarkably consistent across every test generation. In Cinebench R15 multi-core, the Xeon scores 421 versus the Core i3's 366, a 15% advantage. The single-core R15 result shows the same pattern: 59 to 51, a 15.7% edge. This consistency extends to R20 and R23. In Cinebench R20 multi-core, the Xeon posts 1758 against 1527, a 15.1% lead; single-core R20 sees 248 versus 215, a 15.3% gap. The newest test, Cinebench R23, shows the Xeon at 4187 multi-core and 591 single-core, while the Core i3 manages 3637 and 513 respectively, with deltas of 15.1% and 15.2%.

What is striking is not just that the Xeon wins, but that the percentage advantage is so uniform. Whether the workload is single-threaded or fully parallel, the Xeon's lead hovers between 15% and 15.7%. This suggests the performance difference is not tied to core count scaling or frequency behavior, but rather to a fundamental architectural throughput advantage. The Xeon's 6 cores and 12 threads give it a structural edge in multi-threaded tests, yet it also wins single-core tests despite a lower boost clock of 2.67 GHz versus the Core i3's 3.20 GHz. That 15%-plus single-core lead at a 0.53 GHz clock deficit points to significant IPC differences between Westmere and Cannon Lake, or possibly to thermal/power behavior in the mobile chip.

The average benchmark scores tell a similar story on a broader scale. The Xeon E5645 averages 1211 across all benchmark data, while the Core i3-8121U averages 1209. The nearestRivals data confirms they are near-neighbors in overall performance: the Xeon's closest rival is the Core i3-7300T at 1211 with a 0% delta, and the Core i3-8121U itself appears at 1209 with a 0.2% delta. From the Core i3's perspective, the Xeon E5645 is listed at 1211 with a -0.1% delta, meaning the Xeon is essentially its direct peer in aggregate scoring. Both processors sit at the 34th percentile of all CPUs, indicating they occupy the same performance tier despite very different designs.

The Geekbench results, which the Xeon lacks, show the Core i3-8121U scoring 2215 multi-core and 1149 single-core. These numbers are not directly comparable to the Cinebench scores, but they provide additional context for the Core i3's capabilities. The absence of Geekbench data for the Xeon means the head-to-head comparison relies entirely on Cinebench, where the Xeon's advantage is clear and consistent. The wins count is emphatic: 6 for the Xeon, 0 for the Core i3.

The Verdict

The data is unambiguous. The Intel Xeon E5645 outperforms the Intel Core i3-8121U in every benchmark where both were measured. The margin is not trivial; it sits at roughly 15% across the board. Anyone choosing between these two strictly on performance should select the Xeon E5645. The Xeon's 6-core, 12-thread configuration delivers 421 in Cinebench R15 multi-core versus the Core i3's 366, and that advantage persists through R23, where the Xeon hits 4187 against 3637.

However, the verdict is not solely about raw scores. The Xeon E5645 is a server/workstation part from 2010, built on a 32 nm process with an 80 W TDP. The Core i3-8121U is a 15 W mobile chip from 2018, built on Intel's 10 nm process. The Core i3 draws 65 W less power, which is a substantial difference for thermal design and battery life. The Xeon uses DDR3 memory with a triple-channel bus, while the Core i3 uses DDR4 with dual-channel support and a specified memory bandwidth of 38.4 GB/s. The Core i3 also supports PCIe Gen 3 with 16 lanes, whereas the Xeon is limited to PCIe Gen 2.

For a desktop or server workload where power draw is not a constraint, the Xeon is the clear pick. For a mobile system where the 15 W TDP and smaller 70.52 mm² die size matter, the Core i3 is the only realistic option; the Xeon's 80 W TDP and 239 mm² die size are simply not suited to portable designs. The Xeon also supports ECC memory, which the Core i3 does not, making the Xeon the choice for reliability-sensitive server applications. The Core i3's newer architecture brings PCIe Gen 3 and DDR4 support, but the benchmark results show that these modern features do not translate into a performance win in the tested workloads.

Where Each One Wins

The Intel Xeon E5645 wins in every measured performance category. Its 6 cores and 12 threads give it a decisive advantage in multi-threaded rendering workloads, as shown by the Cinebench R15, R20, and R23 multi-core scores. The Xeon also wins single-core tests, posting 59, 248, and 591 in R15, R20, and R23 respectively, against the Core i3's 51, 215, and 513. The Xeon's advantage is consistent regardless of thread count, which suggests it is the better processor for both lightly-threaded and heavily-threaded applications.

The Core i3-8121U's wins are not in performance but in platform characteristics. It has a 15 W TDP versus the Xeon's 80 W, making it suitable for fanless or low-power mobile designs. It supports DDR4 memory with a 38.4 GB/s bandwidth specification, which is a newer and faster memory standard than the Xeon's DDR3. The Core i3 also has PCIe Gen 3 with 16 lanes, compared to the Xeon's PCIe Gen 2. The Core i3's 10 nm process node is more advanced than the Xeon's 32 nm, and its 70.52 mm² die size is substantially smaller than the Xeon's 239 mm². For applications that require low power consumption, modern memory support, or a compact footprint, the Core i3 is the better fit.

The Xeon E5645 also wins on ECC memory support, which is absent on the Core i3. This makes the Xeon the appropriate choice for server environments where data integrity is critical. The Xeon's triple-channel memory bus, while using older DDR3, provides more memory channels than the Core i3's dual-channel DDR4 setup. Both processors are end-of-life, so neither offers a future upgrade path, but the Xeon's server heritage means it is designed for sustained multi-threaded workloads, while the Core i3 is designed for efficiency in mobile contexts.

FAQ

Q: Which processor is faster in multi-core Cinebench R23?

A: The Intel Xeon E5645 scores 4187 in Cinebench R23 multi-core, while the Intel Core i3-8121U scores 3637. The Xeon leads by 15.1%.

Q: Does the Core i3-8121U win any head-to-head benchmark?

A: No. The head-to-head data shows the Xeon E5645 winning all 6 Cinebench comparisons, with the Core i3-8121U recording 0 wins. The Core i3's single-core and multi-core scores are lower in every test.

Q: What is the power consumption difference?

A: The Xeon E5645 has a TDP of 80 W, while the Core i3-8121U has a TDP of 15 W. The Core i3 consumes 65 W less at maximum thermal design power.

Q: Which processor supports ECC memory?

A: The Intel Xeon E5645 supports ECC memory, while the Intel Core i3-8121U does not. This makes the Xeon suitable for error-correcting server workloads.

Q: How do their average benchmark scores compare?

A: The Xeon E5645 has an average benchmark score of 1211, and the Core i3-8121U has an average of 1209. The Xeon's nearest rival data lists the Core i3 at a 0.2% delta, while the Core i3's data lists the Xeon at a -0.1% delta.

Q: What memory types do they support?

A: The Xeon E5645 supports DDR3 with a triple-channel memory bus, while the Core i3-8121U supports DDR4 with a dual-channel bus and a memory bandwidth of 38.4 GB/s.

Architecture Differences

The two processors come from different eras and design philosophies. The Intel Xeon E5645 is based on the Westmere architecture, specifically Westmere-EP, and was released in 2010. It uses a 32 nm process node from Intel's foundry, integrating 1,170 million transistors on a 239 mm² die. The Core i3-8121U is based on Cannon Lake, released in 2018, and uses a 10 nm process node with a die size of 70.52 mm². The Xeon's transistor count is not listed for the Core i3, but the die size difference is substantial.

The core configurations differ significantly. The Xeon has 6 cores and 12 threads, while the Core i3 has 2 cores and 4 threads. The Xeon's base clock is 2.40 GHz with a boost of 2.67 GHz, whereas the Core i3 has a base clock of 2.20 GHz and a boost of 3.20 GHz. Despite the Core i3's higher boost clock, the Xeon wins all Cinebench tests, indicating that the Xeon's additional cores and Westmere architecture provide better throughput in these workloads.

Cache hierarchies are also distinct. Both have 64 KB of L1 cache per core and 256 KB of L2 cache per core. However, the Xeon has 12 MB of shared L3 cache, while the Core i3 has only 4 MB of shared L3 cache. This 8 MB difference in L3 cache likely contributes to the Xeon's consistent performance lead, especially in single-core tests where larger cache can reduce memory latency.

Memory support is a major differentiator. The Xeon uses DDR3 with a triple-channel memory bus and supports ECC memory. The Core i3 uses DDR4 with a dual-channel bus, has a specified memory bandwidth of 38.4 GB/s, and does not support ECC. The Xeon's PCIe support is Gen 2, while the Core i3 supports PCIe Gen 3 with 16 lanes (CPU only). The Core i3's newer memory and PCIe standards reflect its later release date and more advanced process node.

The sockets are incompatible: the Xeon uses Intel Socket 1366, while the Core i3 uses Intel BGA 1440. The Xeon is a server/workstation part with a market segment of Server/Workstation, while the Core i3 is a mobile part. Both are end-of-life and have no integrated graphics. The Xeon's multiplier is locked, and the Core i3's is also locked. The Xeon's part number is SLBWZ, and the Core i3's is SRCVC. The generation labels differ: the Xeon is listed as "Xeon (Westmere-EP)", while the Core i3 is listed as "Core i3 (Kaby Lake-U Refresh)" despite being Cannon Lake architecture. The Core i3's foundry is Intel, and its process node is 10 nm, which is smaller than the Xeon's 32 nm.