Intel Core i5-750S: Since When Does The S Mean Slow?

Intel Core i5-750S: Since When Does The S Mean Slow?

The Core i5-750S is a low-power version of a CPU we often recommend as a solid value for the gamer on a budget: the popular Core i5-750 quad-core, based on Intel's Lynnfield design and widely regarded as a potent overclocker. The S-suffix that represented low-power models is now being used on a processor that, as expected, drops power from the i5's standard 95W TDP. However, it only does so at decreased performance. Is Intel starting to taper off performance in order to hit its lower power consumption figures?

The Intel S Processors

We reviewed the Intel Core 2 Quad Q8200S and Q9550S processors almost a year ago, and they delivered expected levels of performance at decreased idle power and, more importantly, at clearly decreased peak power. What had previously required a 95W thermal envelope fit into a 65W frame with the S-series. The only disadvantage was monetary. For most users, the S might as well have stood for "Soooo expensive!"

A New Kind of S?

While the Core 2 Quad S-models had identical clock speeds and performance as their mainstream siblings, only differing in voltage settings and power consumption, Intel has released an S-model processor that reaches its power savings through performance reduction.

The Core i5-750S does not run at the same 2.66 GHz nominal clock speed as the regular Core i5-750. Instead, the chip is limited to 2.4 GHz. Moreover, there's another drawback with Turbo Boost technology, a key advantage of the Core i5/i7 processors over their predecessors. The i5-750S will not increase the core clock speed for all four cores at all, limiting performance in well-threaded applications, although it still switches to as much as 3.2 GHz for one or two cores.

We compared the Core i5-750 and i5-750S, analyzing their performance, power consumption, and efficiency. This time, the results are less impressive that usual.

Core i7-750S: 82W TDP

Based on exactly the same silicon, the S-model looks and feels like the regular Core i5-750. The main difference in everyday operation is its maximum power, which is limited to 82W instead of the regular 95W. This 13W reduction isn't nearly as impressive as the 30W drop it ensured with the Core 2-class equivalents.

Most likely, the new specifications will limit power consumption and thermal dissipation to levels suited to components created for a 65W power envelope. Idle power isn't an issue, and system peak power consumption is clearly lower on the Core i5-750S than on the regular model. From this perspective, Intel's S-model lives up to expectations.

However, Intel doesn't seem to have introduced any special options that would allow these processors to run at decreased voltage levels. Ultimately, such options are what made all of the existing Core 2 S-class CPUs more efficient.

Intel instead applies a much simpler tweak to bring power down. It reduces the nominal clock speed by 266 MHz and disables the Turbo Boost feature when three or four processing cores are under load. Fortunately, the acceleration feature remains active when only one or two cores are taxed. All voltage levels seem to remain identical, at least on our test system.

We found that the performance impact from reduced clock speeds is pretty noticeable. On one hand, quad-core performance is impacted a bit, which alone isn't much of an issue. The trouble with Turbo Boost only working with one or two cores, though, is that modern operating systems will aggressively distribute threads across all available cores, meaning that in many workloads you will get average workloads on multiple cores. The end result is Turbo Boost staying inactive. Only manual adjustment of thread affinity or true single-threaded applications will yield the Core i5-750S running on par with the regular i5-750. This isn't a caveat we were forced to make previously in analyzing the Core 2s.

CPU-Z Screenshots

Core i5-750 at Idle

Core i5-750 at Peak Multi-Threaded Workload

Running heavily threaded applications pushes Turbo Boost to kick in, which boosts the clock speed by one multiplier increment from 2.66 to 2.80 GHz by setting the multiplier from 20x to 21x. The voltage jumps to 1.192V.

Core i5-750 at Peak Single-Threaded Workload

Finally, a single-threaded application such as WinZip will have the Turbo Boost feature switching one or two cores to a 24x multiplier, resulting in an effective 3.2 GHz core clock speed at 1.256V.

Core i5-750S at Idle

The new S-model isn't any different at idle. A 9x multiplier, 1,200 MHz core clock speed, and 0.872V are very similar to the regular model.

Core i5-750S at Peak Multi-Threaded Workload

Unfortunately, the heavily threaded workload doesn't increase the processor speed beyond 2.40 GHz. This is already 266 MHz less than the base speed on the regular model and clearly impacts performance, as you'll see in the benchmark section. The 1.104V is a bit lower than what the system applied to the Core i5-750 at 2.8 GHz.

Core i5-750S at Peak Single-Threaded Workload

A continuous WinZip workload, which only involves a single processing core, has Turbo Boost switch to 3.2 GHz. Again the voltage is at 1.256V, very much like on the regular Core i5-750 CPU.

System Hardware
Hardware	Details
Performance Benchmarks
Motherboard (Socket LGA1156)	MSI P55-GD65 (Rev. 1.0) Chipset: Intel P55, BIOS: 1.42 (09/08/2009)
CPU Intel	Intel Core i5-750 (45nm, 2.66 GHz, 4 x 256KB L2 and 8MB Shared L3 Cache, TDP 95W, Rev. B1)
CPU Intel II	Intel Core i5-750S (45nm, 2.4 GHz, 4 x 256KB L2 and 8MB Shared L3 Cache, TDP 82W, Rev. B1)
RAM DDR3 (dual)	2 x 2GB DDR3-1600 (Corsair CM3X2G1600C9DHX)
Graphics	Zotac Geforce GTX 260² GPU: Geforce GTX 260 (576 MHz), Graphics RAM: 896MB DDR3 (1,998 MHz), Stream Processors: 216, Shader Clock: 1,242 MHz
Hard Drive	Western Digital VelociRaptor, 300GB (WD3000HLFS) 10,000 RPM, SATA/300, 16MB Cache
Power Supply	PC Power & Cooling, Silencer 750EPS12V 750W
System Software & Drivers
Operating System	Windows Vista Enterprise Version 6.0 x64 Service Pack 2 (Build 6000)
Drivers and Settings
Intel Chipset Drivers	Chipset Installation Utility Ver. 9.1.1.1015
Intel Storage Drivers	Matrix Storage Drivers Ver. 8.8.0.1009

Audio Benchmarks and Settings
Benchmark	Details
iTunes	Version: 8.1.0.52, Audio CD ("Terminator II" SE), 53 min., Convert to AAC audio format
Lame MP3	Version 3.98 Audio CD "Terminator II SE", 53 min. convert WAV to MP3 audio format Command: -b 160 --nores (160 Kbps)
Video Benchmarks Settings
Benchmark	Details
TMPEG 4.6	Version: 4.6.3.268 Video: Terminator 2 SE DVD (720x576, 16:9) 5 Minutes Audio: Dolby Digital, 48000 Hz, 6-channel, English Advanced Acoustic Engine MP3 Encoder (160 Kbps, 44.1 KHz)
DivX 6.8.5	Version: 6.8.5 == Main Menu == default == Codec Menu == Encoding mode: Insane Quality Enhanced multi-threading Enabled using SSE4 Quarter-pixel search == Video Menu == Quantization: MPEG-2
XviD 1.2.1	Version: 1.2.1 Other Options / Encoder Menu - Display encoding status = off
Mainconcept Reference 1.6.1	Version: 1.6.1 MPEG-2 to MPEG-2 (H.264) MainConcept H.264/AVC Codec 28 sec HDTV 1920x1080 (MPEG-2) Audio: MPEG-2 (44.1 kHz, 2-Channel, 16-Bit, 224 Kbps) Codec: H.264 Mode: PAL (25 FPS) Profile: Settings for eight threads
Application Benchmarks and Settings
Benchmark	Details
Grisoft AVG Anti-Virus 8	Version: 8.5.287 Virus base: 270.12.16/2094 Benchmark Scan: some compressed ZIP and RAR archives
Winrar 3.9	Version 3.90 x64 BETA 1 Compression = Best Benchmark: THG-Workload
Winzip 12	Version 12.0 (8252) WinZip Commandline Version 3 Compression = Best Dictionary = 4096KB Benchmark: THG-Workload
Autodesk 3ds Max 2009	Version: 9 x64 Rendering Dragon Image Resolution: 1920 x 1280 (frame 1-5)
Adobe Photoshop CS 4 (64 bit)	Version: 11 Filtering a 16MB TIF (15000x7266) Filters: Radial Blur (Amount: 10; Method: zoom; Quality: good) Shape Blur (Radius: 46 px; custom shape: Trademark sysmbol) Median (Radius: 1px) Polar Coordinates (Rectangular to Polar)
Adobe Acrobat 9 Professional	Version: 9.0.0 (Extended) == Printing Preferenced Menu == Default Settings: Standard == Adobe PDF Security - Edit Menu == Encrypt all documents (128-bit RC4) Open Password: 123 Permissions Password: 321
Microsoft Powerpoint 2007	Version: 2007 SP2 PPT to PDF Powerpoint Document (115 Pages) Adobe PDF-Printer
Deep Fritz 11	Version: 11 Fritz Chess Benchmark Version 4.2

System Details: MSI P55-GD65 and Zotac GeForce GTX 260²

Benchmark Results: Applications

Checking for viruses using AVG requires only slightly more time on the Core i5-750S. However, this program does not take significant advantage of multi-core processors.

3ds Max taxes all available cores, and since four cores run at 2.4 GHz on the Core i5-750S versus 2.80 GHz on the regular Core i5-750 we see quite a difference in effective performance.

Creating a PDF document out of a 115-page PowerPoint presentation takes a bit more time on the Core i5-750S.

Photoshop also shows quite a negative impact on the Core i5-750S.

WinRAR is well-optimized for multiple cores, so the difference is smaller.

WinZip only takes advantage of a single processing core and hence we saw almost identical results on the Core i5-750S and the regular Core i5-750 version.

Fritz 11 chess wants as many cores and as much clock speed as it can get. As a result, the difference is rather significant.

Benchmark Results: Audio/Video

Lame has some optimizations to run on two threads in parallel, but it takes little advantage of it. Therefore, we have a tie.

DivX video transcoding runs faster on the regular version CPU.

There are no differences on Xvid transcoding.

Conclusion

Intel has a solid track record for releasing new processor steppings that deliver the same performance at reduced power levels. Prior-generation S-model Core 2 processors allowed select processors to run at decreased voltage levels in an effort to reduce system power consumption. But with the Core i5-750S, the tune is changing.

The Core i5-750S only reaches its lower power levels through a solid reduction in nominal clock speed and a limitation of the Turbo Boost feature, all in an effort to keep the processor well within the specified thermal envelope of 83W. People looking for a Core i5 quad-core product that works within certain power consumption restrictions will appreciate the Core i5-750S, even with its price premium. While the regular model costs $196 and up, expect to spend roughly $259 on the "power optimized" version. Though that's a smaller price hike versus past Core 2-based S-class CPUs, it's still a significant premium for a slower component.

The new chip only delivers its benefits if low power is the only criteria. Everyone who still wants performance or even efficiency, measured in performance per watt, will probably be as disappointed as we were. Intel decided to cut back clock speeds to deliver a low-power processor, but the firm doesn't seem to bothered that the S-model processors actually deliver worse power efficiency than the regular models. We believe this should not be the case.

The fact that you cannot rely on a processor's model number anymore to be able to estimate its performance or clock speed is pretty discouraging. It forces almost every user to look at the specifications before making any move. Car manufacturers such as BMW and Mercedes stopped matching model numbers with engine sizes long ago, so perhaps we should be tolerant enough to accept this. However, spending a lot of money on a supposedly energy-efficient product, only to see it spanked by the regular product in key tests, leaves a bitter aftertaste. You decide what the S means now.

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