Core i3-8121U vs Core i5-6400T

PassMark CPU Mark evaluates processor speed through complex mathematical computations. It provides a reliable metric to compare multi-core performance, where higher scores indicate faster processing for multitasking, gaming, and heavy workloads.

Core i3-8121U vs Core i5-6400T FPS Benchmarks

Predicted gaming performance across popular games. Tested paired with GeForce RTX 5090 to isolate CPU performance.

Search any supported game below to compare 1080p FPS for both components.

Core i3-8121U vs Core i5-6400T: Pros, Cons & Final Verdict

See where each CPU makes more sense in practice: gaming, heavier work, platform cost, power draw, and upgrade path.

Core i3-8121U

2018

Why buy it

✅+24% higher Geekbench single-core performance for gaming and desktop responsiveness.

Trade-offs

❌Lower Geekbench multi-core (2,250 vs 2,600).
❌Smaller total L3 cache (4 MB vs 6 MB).
❌1400% higher power demand at 15W vs 1W.
❌No integrated graphics, while Core i5-6400T can still boot and troubleshoot without a discrete GPU.
❌No boxed cooler included, unlike Core i5-6400T.

Core i5-6400T

2015

Why buy it

✅+15.6% higher Geekbench multi-core.
✅+50% larger total L3 cache (6 MB vs 4 MB).
✅Draws 1W instead of 15W, a 14W reduction.
✅Integrated graphics onboard with HD 530, while Core i3-8121U needs a discrete GPU.
✅Includes a boxed cooler (Yes), unlike Core i3-8121U.

Trade-offs

❌Lower Geekbench single-core performance for gaming (950 vs 1,178).
❌Launch MSRP is still $192 MSRP, while Core i3-8121U mostly shows up through inconsistent older-market listings.

Quick Answers

So, is Core i5-6400T better than Core i3-8121U?

It depends on what you want from the system. For gaming, Core i3-8121U is ahead with a 0.2% average FPS lead across 50 shared CPU game tests in our data. For rendering, compiling, streaming, and heavier multitasking, Core i5-6400T pulls ahead with 15.6% better Geekbench multi-core. Core i5-6400T also has the bigger cache pool with 50% larger total L3 cache (6 MB vs 4 MB).

Which one is better for streaming, content creation, and heavy multitasking?

For streaming, content creation, and heavier multitasking, Core i5-6400T is the stronger fit. You are getting 15.6% better Geekbench multi-core, backed by 4 cores and 4 threads. It also has the larger cache pool with 50% larger total L3 cache (6 MB vs 4 MB).

Which one is the smarter buy today, not just the cheaper CPU?

Core i5-6400T is the better buy right now. Core i5-6400T comes in at an unclear MSRP at $192 MSRP versus unclear MSRP, and it still gives you 15.6% better Geekbench multi-core. The compromise is that Core i3-8121U is still the better pure gaming CPU with a 0.2% average FPS lead across 50 shared CPU game tests in our data. It is also 100.0% better value on MSRP (22.1 vs 0.0 PassMark/$), so you are getting the faster CPU without taking a value hit on paper.

Which one is more future-proof for 2026 and beyond?

Core i3-8121U makes more sense long term for 2026 and beyond. You are getting a newer CPU generation (2018 vs 2015). That makes it the safer long-term bet.

Core i3-8121U vs Core i5-6400T Technical Specifications

Side-by-side specs, architecture details, clocks, memory, power, and platform differences.

Core i3-8121U

The Core i3-8121U is manufactured by Intel. It was released in 5 May 2018 (7 years ago). It is based on the Coffee Lake-U (2018−2019) architecture. It features 2 cores and 4 threads. Base frequency is 2.2 GHz, with boost up to 3.2 GHz. L3 cache: 4 MB (total). L2 cache: 256K (per core). Built on 10 nm process technology. Socket: BGA1440. Thermal design power (TDP): 15 Watt. Memory support: DDR4. Passmark benchmark score: 4,271 points. Launch price was $69.

Core i5-6400T

The Core i5-6400T is manufactured by Intel. It was released in 1 September 2015 (10 years ago). It is based on the Skylake (2015−2016) architecture. It features 4 cores and 4 threads. Base frequency is 2.2 GHz, with boost up to 2.8 GHz. L3 cache: 6 MB. L2 cache: 1 MB. Built on 14 nm process technology. Socket: LGA1151. Thermal design power (TDP): 35 Watt. Memory support: DDR3, DDR4. Passmark benchmark score: 4,243 points. Launch price was $192.

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Processing Power

The Core i3-8121U packs 2 cores / 4 threads, while the Core i5-6400T offers 4 cores / 4 threads — the Core i5-6400T has 2 more cores. Boost clocks reach 3.2 GHz on the Core i3-8121U versus 2.8 GHz on the Core i5-6400T — a 13.3% clock advantage for the Core i3-8121U (base: 2.2 GHz vs 2.2 GHz). The Core i3-8121U uses the Coffee Lake-U (2018−2019) architecture (10 nm), while the Core i5-6400T uses Skylake (2015−2016) (14 nm). In PassMark, the Core i3-8121U scores 4,271 against the Core i5-6400T's 4,243 — a 0.7% lead for the Core i3-8121U. Geekbench 6 single-core — the metric most relevant to gaming — records 1,178 vs 950, a 21.4% lead for the Core i3-8121U that directly translates to higher frame rates. Multi-core Geekbench: 2,250 vs 2,600 (14.4% advantage for the Core i5-6400T). L3 cache: 4 MB (total) on the Core i3-8121U vs 6 MB on the Core i5-6400T.

Feature	Core i3-8121U	Core i5-6400T
Cores / Threads	2 / 4	4 / 4+100%
Boost Clock	3.2 GHz+14%	2.8 GHz
Base Clock	2.2 GHz	2.2 GHz
L3 Cache	4 MB (total)	6 MB+50%
L2 Cache	256K (per core)+25500%	1 MB
Process	10 nm-29%	14 nm
Architecture	Coffee Lake-U (2018−2019)	Skylake (2015−2016)
PassMark	4,271	4,243
Cinebench R23 Multi	—	2,200
Geekbench 6 Single	1,178+24%	950
Geekbench 6 Multi	2,250	2,600+16%

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Memory & Platform

The Core i3-8121U uses the BGA1440 socket (PCIe 3.0), while the Core i5-6400T uses LGA1151 (PCIe 3.0) — making them incompatible on the same motherboard. Maximum memory speed reaches DDR4-2400 on the Core i3-8121U versus DDR4-2133 on the Core i5-6400T — the Core i3-8121U supports 12.5% faster memory, which can translate to measurable gains in memory-sensitive workloads. The Core i5-6400T supports up to 64 GB of RAM compared to 32 GB — 100% more capacity for professional workloads. Both feature 2-channel memory with ECC support. Both provide 16 PCIe lanes. Chipset compatibility: SoC (Core i3-8121U) and H110,B150,H170,Z170,Z270 (Core i5-6400T).

Feature	Core i3-8121U	Core i5-6400T
Socket	BGA1440	LGA1151
PCIe Generation	PCIe 3.0	PCIe 3.0
Max RAM Speed	DDR4-2400+13%	DDR4-2133
Max RAM Capacity	32 GB	64 GB+100%
RAM Channels	2	2
ECC Support	No	No
PCIe Lanes	16	16

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Advanced Features

Neither processor supports overclocking. Only the Core i3-8121U supports AVX-512 instructions — important for machine learning and scientific applications. Virtualization support: VT-x, VT-d, EPT (Core i3-8121U) vs VT-x, VT-d (Core i5-6400T). The Core i5-6400T includes integrated graphics (HD 530), while the Core i3-8121U requires a dedicated GPU. Primary use case: Core i3-8121U targets Productivity, Core i5-6400T targets Budget. Direct competitor: Core i3-8121U rivals Core i3-8130U; Core i5-6400T rivals Core i3-7100.