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Intel Core i3-2100T & Core i5-2400S Low Power CPUs

Intel Core i3-2100T and Core i5-2400S processors have a rated speed of just 2.5 GHz, but the i5-2400S has some crazy Turbo Boost speeds, and they both have TDPs 30W lower than their standard counterparts.

May 23, 2011 by Lawrence Lee

Product
Core i3-2100T
LGA1155 Processor
Core i5-2400S
LGA1155 Processor
Manufacturer
Street Price
US$130
US$195

In recent years, both Intel and AMD have been releasing specially binned chips with lower power requirements than the standard desktop models. These parts are often used by large system integrators to build energy efficient PCs for corporations with an eco-conscience. They are also of interest to DIY users like SPCR enthusiasts who use the energy and thermal advantage of these chips to build smaller and/or quieter machines. Typically these processors are priced higher and clocked lower, compared to the standard chips.


The i5-2400S and i3-2100T.

The Intel Core i3-2100T and Core i5-2400S carry just a $10 surcharge but the clock speed penalty is a bit bigger. Both have a rated speed of just 2.5 GHz (there is only one other sub-3GHz Sandy Bridge desktop chip currently) compared to the standard Core i3-2100 and Core i5-2400 which operate at 3.1 GHz. However the rated thermal design power (TDP) of these chips is 30W lower than their mainstream cousins — a staggering amount given the superb energy efficiency of regular Sandy Bridge CPUs. Is there really room for that much improvement?

Intel Desktop LGA1155 CPU Comparison
Model
Speed
L3
Cache
TDP
Features
Street Price
Core i3-2100
3.1 GHz
3MB
65W
N/A
$120
Core i3-2100T
2.5 GHz
3MB
35W
N/A
$130
Core i3-2120
3.3 GHz
3MB
95W
N/A
$140
Core i5-2300
2.8 GHz
6MB
95W
TB
$180
Core i5-2400
3.1 GHz
6MB
95W
TB
$185
Core i5-2400S
2.5 GHz
6MB
65W
TB
$195
Core i5-2500
3.3 GHz
8MB
95W
TB
$210
Core i5-2500K
3.3 GHz
8MB
95W
TB,UL
$215
Core i7-2600
3.4 GHz
8MB
95W
HT, TB
$295
Core i7-2600K
3.4 GHz
8MB
95W
HT,TB,UL
$310
UL = unlocked multiplier, HT = Hyper-threading,
TB = Turbo Boost

 

Model
Rated Speed
Turbo Boost Speeds
1 Core
2 Cores
3 Cores
4 Cores
Core i5-2400
3.1 GHz
3.4 GHz
3.3 GHz
3.3 GHz
3.2 GHz
Core i5-2400S
2.5 GHz
3.3 GHz
3.2 GHz
2.8 GHz
2.6 GHz

The more intriguing part is the i5-2400S, as it is supercharged with very high Turbo Boost frequencies (this couldn’t not be done for the i3-2100T as i3 chips lack Turbo Boost altogether). The i5-2400 has typical Turbo Boost speeds, overclocking by just 100~300 MHz depending on how many cores are active. The i5-2400S gets much larger bumps, 800 MHz for one core, 700 MHz for two cores, and 300 MHz for three cores. This means the i5-2400S will only be slightly behind the i5-2400 in speed much of the time. This is a huge advantage compared to the i3-2100T which trails the i3-2100 by 600 MHz in all loads.

The CPU cost is only one part of the equation. You can’t discuss value without including motherboard cost, which varies from socket to socket. In the table above, we added the street price of the chips we’re comparing today with the average price of a compatible motherboard from Newegg (we chose Intel/Asus/Gigabyte/MSI DDR3 microATX and ATX models, omitting the most expensive/extravagant ones). It turned out to be US$93 for AM3, US$119 for LGA1156, and US$139 for LGA1155.



The i5-2400 undervolted to the same core voltage as the i5-2400S, 1.080V according to CPU-Z.

To make things interesting, we will also undervolt the Core i5-2400 to approximately the same core voltage used by the i5-2400S by setting an offset voltage of -0.090V on our Asus P8P67 test board. It’s a simple thing to do, and may be a worthwhile alternative if it gives us similar results. Ideally we would run i5-2400 at the exact same voltage/speeds as the i5-2400S, but we weren’t able to match its odd Turbo Boost multipliers (+8, +7, +3, +1).

TEST METHODOLOGY

Common Test Platform:

Intel LGA1156:

Intel LGA1155:

AMD AM3:

Measurement and Analysis Tools

Timed Benchmark Test Details

  • NOD32: In-depth virus scan of a folder containing 32 files of varying
    size with many RAR and ZIP archives.
  • WinRAR: Archive creation with a folder containing 68 files of varying
    size (less than 50MB).
  • iTunes: Conversion of an MP3 file to AAC.
  • TMPGEnc: Encoding a XVID AVI file with VC-1.
  • HandBrake: Encoding a XVID AVI file with H.264.
  • Photoshop: Image manipulation using a variety of filters, a derivation
    of Driver Heaven’s Photoshop
    Benchmark V3
    (test image resized to 4500×3499).

1080p | 24fps | ~14mbps

x264 1080p: Spaceship is a 1080p x264 clip encoded from the
Blu-ray version of an animated short film. It features a hapless robot
trying to repair a lamp on a spaceship.

Testing Procedures

Our main test procedure is a series of benchmarks, timed tests of real-world applications. System power consumption (AC) is measured with a Seasonic Power Angel during these tests (an average of the first 10~15 seconds) as well as at idle, during playback of a 1080p H.264 encoded clip, and during full CPU load. To stress the CPU we use either either Prime95 (large FFTs setting) or CPUBurn depending on which
produces higher system power consumption. The AC system power is then later converted to DC.

Certain services and features like Superfetch and System Restore are disabled
to prevent them from affecting our results. Aero glass is left enabled if supported.
We also make note if energy saving features like Cool’n’Quiet and SpeedStep
do not function properly.

Estimating DC Power

The following power efficiency figures were obtained for the
Seasonic SS-400ET used in our test system:

Seasonic SS-400ET Test Results
DC Output (W)
21.2
41.6
60.2
81.9
104.7
124.1
145.2
AC Input (W)
32.0
58.0
78.0
102.0
128.0
150.0
175.0
Efficiency
66.3%
71.7%
77.1%
80.3%
81.8%
82.8%
83.0%

This data is enough to give us a very good estimate of DC demand in our
test system. We extrapolate the DC power output from the measured AC power
input based on this data. We won’t go through the math; it’s easy enough
to figure out for yourself if you really want to.

Operating Voltages

Before we jump into our test results, please note the operating voltages
of the processors tested today as sort of a disclaimer. Different samples of
the same processor often run at slightly different operating voltages which
can affect energy efficiency. Different motherboard models do not apply the exact same core voltage either. Higher voltages don’t necessarily equate to higher power consumption, but in many cases there is a correlation.

TEST RESULTS

System Power

Our first test is low load system power consumption, at idle and during video playback. While some users work their systems hard, other machines are often left idling or used for mundane tasks like watching video or surfing the web for hours on end.

At idle and during video playback using discrete graphics, the i3-2100T, undervolted i5-2400, and i5-2400S were a tad more frugal than i3-2100 and i5-2400, but the difference was just one watt.

On a theoretical full load, the i3-2100T and i5-2400S used 12W and 14W less respectively than its similarly-named counterparts. However, the undervolted i5-2400 did quite well, consuming only 4W more than the i5-2400S and with a much higher clock speed too.

Thermals

For our thermal test, each CPU was paired with the Scythe Kabuto with its stock
fan spinning at ~800 rpm. AMD temperatures were taken using the motherboard’s
sensor via SpeedFan and Intel temperatures were taking with RealTemp.


*Note: direct temperature comparisons between Intel and AMD processors should not be made.

On load, the i5-2400 was 5°C warmer than the i5-2400S, while the difference was only 2°C when undervolted. The i3-2100 and i3-2100T ran the coolest at just 19°C above ambient.

General Performance

In Photoshop, high Turbo Boost speeds allowed the i5-2400S’ to finish the test just 4 seconds later than the i5-2400. The i3-2100T finished 22 seconds behind the i3-2100, about 20% slower. Despite its low clock speed, the i3-2100T still had a very impressive showing against AMD’s offerings.

The Core i3’s don’t fare nearly as well in the NOD32 test, so the i3-2100T’s low clock speed really hurts it by comparison. It finished 18% slower than the i3-2100, finishing dead last, but used 6W less. The i5-2400S trailed the i5-2400 by just 12 seconds.

In WinRAR, the i3-2100T closed the gap with i3-2100, completing the task 12% slower. The i5-2400S continued to impress, being edged out by the i5-2400 by only 5 seconds. The undervolted i5-2400 of course performed the same, but as a bonus, had a 4W power advantage, even beating the i5-2400S by 3W.

Encoding Performance

More of the same for the i5-2400S in iTunes AAC encoding, following close behind the i5-2400 in performance. The i3-2100T on the other hand continued to struggle, completing the encode 19% slower than the i3-2100.

Our TMPGEnc test is the only one where the i3-2100T impressed us, finishing only 7% behind the i3-2100, and using 13W less in the process. In a bit of a role reversal, the i5-2400S faltered, completing the task 20% slower than the i5-2400 as the clock speed for the i5-2400S is only 2.6 GHz when all cores are in operation. It did use 9W less, so it seems the heavier the load, the more greater the energy savings.

The i3-2100T stumbled once again in HandBrake, this time finishing 23% slower than the i3-2100, albeit with a 10W power consumption advantage. Similarly the i5-2400S took 21% longer but used 14W less than the i5-2400. The undervolted i5-2400 cut the power difference in half.

Performance Analysis

We arrived at our overall performance score by weighing each test equally (each composing 1/6 of the total). Mathematically, a processor that finishes first in every single test would receive a score of 100. The i5-2400 came close, with a score of 99.1 as it was defeated in just one test by the X6 1100T by a small margin.

Thanks to its aggressive Turbo Boost settings, the i5-2400S doesn’t fall far behind the i5-2400 in overall speed, and it still managed to fight off AMD’s best processors in our test suite. As all desktop Core i3s lack Turbo Boost, the i3-2100T didn’t fare nearly as well compared to the i3-2100, about 15% slower in our tests. It is noteworthy, however, that even at 2.5 GHz, it edged out AMD’s current fastest dual core CPU, the X2 565. Needless to say, we hope the arrival of Bulldozer will change AMD’s fortunes.

The i3-2100T used less power than the i3-2100, but took longer to run through our benchmarks and thus used more power in total. The same can be said of the i5-2400S vs. the i5-2400, though the margin was slimmer as the performance difference was relatively small.

We derived our average system power consumption by assuming that half the time our test system would be on low load (an average of the power consumption when sitting idle and playing H.264 video) and the other half would be spend on heavy load (the average power consumption of our five measured benchmarks). With this usage pattern, the Sandy Bridge processors consume between 50W and 60W, while AMD’s best, the X4 840 uses 13~21W more. The i5-2400S is neck-and-neck with the undervolted i5-2400, while the i3-2100T is 5W more efficient on average.

Value

To create a value score, we divided the “overall performance” figure from earlier by the street cost of the CPU and an average motherboard, and adjusted it so the winner would have a score of 100.

Though losing to Intel in raw performance and energy efficiency, with cheap CPU and motherboard pricing, per dollar, many AMD chips are better buys. The Phenom II X4 840, 955, and 965 are all excellent values unless your electricity costs are really high. The i5-2400 and i3-2100T fall 10 and 17 points short of their vanilla contemporaries and their US$10 price premium doesn’t help.

If energy efficiency is more important to you, here we present “overall performance” divided by “average system power consumption,” again adjusted so the winner would have a score of 100. This time, Sandy Bridges rise to the top and the Phenoms sink to the bottom.

FINAL THOUGHTS

Of the two low power processors we tested today, the Core i5-2400S is the worthier candidate as its aggressive Turbo Boost frequencies provide a big performance bump. By the book, the i5-2400S has a 600 MHz disadvantage compared to the i5-2400, but in our test suite it was only 9% slower. Only on a heavy threaded workload does it show any significant performance lag against the standard i5-2400. $195 for the S version versus $185 for the standard i5-2400 is not an onerous cash bump. Still, the power consumption difference is slim enough that an i5-2400 with a small undervolt will deliver similar results without sacrificing any speed. This has been our biggest criticism of these specialty low power processors — you can create your own with simple undervolting on a decent motherboard.

The performance gap between the Core i3-2100 and i3-2100T is much wider, about 15%, as there are no crazy Turbo Boost speeds to help even the odds. However, the i3-2100T is still more than a match for AMD’s dual core processors and slower Lynnfield models. With a typical workload, it consumes about 5W less than the i3-2100, but the difference at idle is too small to count. If you’re going to build a system that’s going to idle mostly, there’s really no advantage. You can always try undervolting to have your cake and eat it too. The i3-2100T sells for just $10 more than the i3-2100, about US$130, but the performance penalty is much higher than the i5-2400/2400S, so it is harder to justify.

Our thanks to Intel and AMD
and for processor samples used in this review.

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Articles of Related Interest
Intel Core i3-2100 vs. AMD Phenom II X2 565
Asus E35M1-M Pro: AMD Fusion Motherboard
Sandy Bridge, Part 4: Core i5-2400, i5-2500K and i7-2600K CPUs
AMD Athlon II X3: Affordable Compromise
Athlon II X4 610e & Phenom II X4 910e: 45W & 65W Quad Cores
Intel Core i5-661: A 32nm CPU with Integrated Graphics

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