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Xeon E5‑2666 v3 is a compelling option for home builds. This OEM‑only SKU was made for Amazon servers and later appeared on the used market at a reasonable price.
Compared with other Xeon E5 v3 CPUs, it stands out for its high all‑core frequency with Turbo Boost Unlock (TBU) and for supporting both DDR4 and DDR3 (not simultaneously).
Specifications
| Model | Xeon e5 2666 v3 |
|---|---|
| Socket | LGA2011-3 |
| Release Date | Q3 2014 |
| Architecture | Haswell-EP, 22 nm |
| Cores / Threads | 10 / 20 |
| Memory support | DDR3-1866, 4-channel DDR4-2133, 4-channel |
| Base Frequency | 2900 MHz |
| Max Turbo Frequency | 3500 MHz (1 Core) 3200 MHz (2-10 Cores) |
| Extensions & Features | MMX instructions SSE / Streaming SIMD Extensions SSE2 / Streaming SIMD Extensions 2 SSE3 / Streaming SIMD Extensions 3 SSSE3 / Supplemental Streaming SIMD Extensions 3 SSE4 / SSE4.1 + SSE4.2 / Streaming SIMD Extensions 4 AES / Advanced Encryption Standard instructions AVX / Advanced Vector Extensions AVX2 / Advanced Vector Extensions 2.0 BMI / BMI1 + BMI2 / Bit Manipulation instructions F16C / 16-bit Floating-Point conversion instructions FMA3 / 3-operand Fused Multiply-Add instructions EM64T / Extended Memory 64 technology / Intel 64 HT / Hyper-Threading technology VT-x / Virtualization technology VT-d / Virtualization for directed I/O TBT 2.0 / Turbo Boost technology 2.0 NX / XD / Execute disable bit ? TXT / Trusted Execution technology Enhanced Intel SpeedStep technology |
| L3 Cache | 25 Mb |
| PCIe Lanes | 40, Gen 3.0 |
| TDP | 135 W |
| Maximum operating temperature | 79°C |
| Multiplier | Locked |
| Integrated Graphics | None |
| CPUID | 0x306F2 |
| Approximate Price | $20 - $30 (Aliexpress) |
- 10 cores and good multi‑threaded performance
- High all‑core frequency with TBU
- Support for both DDR4 and DDR3 (not simultaneously)
- Low price on the used market
Main disadvantages:
- Aging architecture; lower IPC versus modern CPUs
- High heat output under TBU
- Requires a robust VRM; not recommended for low‑end boards
- Memory limited to DDR4‑2133 or DDR3‑1866 (quad‑channel helps with bandwidth)
Xeon E5‑2666 v3 is one of the few E5 v3 CPUs whose memory controller supports both DDR3 and DDR4. Because bandwidth of DDR4‑2133 and DDR3‑1866 is close, using DDR3 can be reasonable in some builds.
Overclocking Capability
Turbo Boost Unlock
Turbo Boost Unlock on Xeon E5 v3 forces the maximum single‑core turbo ratio across all cores. It leverages an undocumented Haswell‑EP quirk, not an official feature. Applied via methods such as a BIOS mod with S3TurboTool, it typically yields 10–30% multi‑threaded gains, depending on SKU and cooling. Expect higher sustained power and temperatures; use strong cooling and make sure the motherboard VRM can handle the load.
TBU is widely used in the X99 community; without it, performance in many modern apps and games is often insufficient.
Base Clock (BCLK) Overclocking
Some retail X99 boards allow a small BCLK increase (about 3–5%), which brings only minor gains. It can be used alone or together with TBU.
Performance and Tests
All tests below were run with TBU enabled. Multi‑threaded performance is strong; per‑core speed is still far from modern CPUs.
CPU‑Z
Cinebench R15, R20, R23
CPU Mark
Blender (BMW)
AIDA64 CPU Queen
Corona 1.3
Summary
| Xeon E5 2666 v3 (TBU) | |
|---|---|
| CPU-Z (single) | ~390 |
| CPU-Z (multi) | ~4900 |
| Cinebench R15 | ~1650 |
| Cinebench R20 | ~3850 |
| Cinebench R23 | ~9800 |
| CPU Mark | ~8700 |
| Blender (BMW) | ~03:32 |
| AIDA64 CPU Queen | ~99500 |
| Corona 1.3 | ~02:00 |
Similar models in terms of multi‑threaded performance level:
| Model | Cores / Threads | Cinebench R15 | Cinebench R20 | Cinebench R23 | CPU-Z Multi |
|---|---|---|---|---|---|
| Xeon E5-2666 v3 | 10c / 20t | ~1700 | ~3900 | ~9800 | ~4900 |
| Xeon E5-2667 v4 | 8c / 16t | ~1500 | ~3400 | ~8600 | ~4100 |
| Ryzen 5 3600 | 6c / 12t | ~1600 | ~3700 | ~9900 | ~4800 |
| Ryzen 7 2700 | 8c / 16t | ~1500 | ~3400 | ~9500 | ~4400 |
| Core i7-9700 | 8c / 8t | ~1700 | ~3800 | ~9600 | ~4700 |
Gaming Performance
The high all‑core frequency makes this CPU one of the better gaming choices within the Xeon E5 v3 series. It delivers smooth FPS in most esports titles, and many demanding single‑player games run well. Do not expect comfortable performance in heavy Unreal Engine 5 projects, but paired with a mid‑range GPU it can serve as a solid budget gaming option.
- Games up to 2020: 95% run well (60+ FPS), 5% are playable (40–60 FPS)
- Games 2020–2025: 80% run well (60+ FPS), 10% are playable (40–60 FPS), 10% are unplayable (low FPS, stutter)
Most suitable graphics cards for FullHD and 1440p: NVIDIA 1070 (Ti), 1660 (Super/Ti), 1080 (Ti), 2060 (Super), 3060 (Ti); AMD RX 580, RX 5600 XT, RX 5700 XT, RX 6600 (XT/6650 XT), RX 6700 XT, RX 7600 (XT).
Gaming performance with RX 6600:
Close Alternatives
High‑frequency Xeon E5 processors:
- Xeon E5 2667 v4 — 8/16, 3.5 GHz all‑core. Slightly better in games; a bit weaker in heavy multi‑thread.
- Xeon E5 2689 v4 — 10/20, 3.7 GHz all‑core. One of the highest‑frequency LGA2011‑3 CPUs, but expensive and with high TDP.
- Xeon E5 2690 v4 — 14/28, 3.2 GHz all‑core. Well‑rounded: strong for work and acceptable for games.
See the complete LGA2011‑3 CPU list.
Revisions
Besides the retail version, there are engineering samples of the E5‑2666 v3. They can be identified by the s‑spec code laser‑marked on the heatspreader (IHS). The retail unit is SR1Y7 (stepping M1). The revision is also shown in the HWiNFO utility. 
Frequently Asked Questions
Is undervolting possible?
Yes, voltage control is possible on v3 processors. Some ES models may be exceptions.
Is there solder or thermal paste under the lid?
There is solder under the lid, as with the entire Xeon E5 v3/v4 lineup.
Is the processor compatible with Win11?
No, the Xeon E5‑2666 v3 is not officially supported by Windows 11, but it works if you bypass the CPU and TPM checks during installation.
Final Verdict
Xeon E5‑2666 v3 offers very good price‑to‑performance for used X99 builds. It handles games and everyday workloads well once TBU is applied, but runs hot and needs a capable VRM and cooling. If you prefer cooler and more efficient options without unlock mods, consider E5‑2667 v4; despite fewer cores, it matches or beats gaming results and is easier on entry‑level motherboards.