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

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

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).



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