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Samsung Galaxy S4 CPU – How its Exynos 5 Octa-core chip works

Andrew Williams


Samsung Galaxy S4 CPU – How its Exynos 5 Octa-core chip works
Exynos 5

One of the most technically interesting parts of the Samsung Galaxy S4 is its Octa-core Exynos 5 CPU. Yes, that means eight cores – the same number we’ll see in the forthcoming Sony PS4.

However, it’s not quite as simple as a “pure” eight-core processor. It uses ARM’s big.LITTLE architecture, and is really more accurately thought of as two quad-core processors that work together rather than a single gut-busting 8-core chip.

With Great Performance Comes Great Responsibility

One of the quad-core setups is a team of performance cores using the Cortex-A15 architecture. This is the same type of chipset used in the iPhone 5’s Apple A6 chip, and it’s pretty darn powerful.

This set of four performance cores is clocked at 1.6GHz in the UK version of the Samsung Galaxy S4. The phone could make do with just these four cores. But the truth of the matter is that a lot of the time, this setup is pure overkill.

This overkill results in poor power efficiency. And that means a phone that’ll probably drain its battery within a day. No-one wants that.

This is where the second set of cores come in. The efficiency cores use Cortex-A7 architecture. It’s in the same processor family and uses the same “core” architecture as the other quartet of cores, but is designed for lower-powered applications. It’s better geared towards everyday tasks – flicking through the Android UI in other words.

When the load gets that bit too much for the 1.2GHz Cortex-A7 cores, the Exynos 5 processor will automatically start switching over to the performance cores. It works as a game of tag, one set of cores replacing another rather than having the whole lot rowing the Exynos boat at the same time. However, this may change as software updates are applied, to both TouchWiz and Android.

Week-long battery life? Not Quite

This three-part system architecture, when you include the GPU, should result in pretty impressive power efficiency matched with blazing performance. However, if you think this will grant us week-long battery life, think again.

The clever Exynos 5 SoC is here to offset other elements of the phone.

First of all comes Samsung’s obsession with slim-ness. The Samsung Galaxy S4 is an extremely thin phone – almost a full millimetre thinner than the Galaxy S3. If you want to get very slim and very light, you can’t incorporate that large a battery.

The Samsung Galaxy S4’s battery has a capacity of 2,600mAh. In fairness to Samsung, that’s larger than that of the Sony Xperia Z or HTC One, this phone’s fiercest Android rivals. However, it’s a way short of the 3,100mAh monster in the Galaxy Note 2. One of the reasons we, and many others, love that phone so much is its fab battery life.

Just as important is quite how draining the Galaxy S4's 1080p screen will be. The Samsung Galaxy S4 uses a nifty 5-inch Super AMOLED screen. It’s more advanced than the screen of the Samsung Galaxy S3, and is said to use a more power-efficient panel. However, this will be efficient relative to its specs.

There’s no getting around the fact that the Galaxy S4’s screen is massive and absolutely jam-packed with pixels – each of which acts as its own light source thanks to the way AMOLED screens function.

Octa-core – Marketing Magic or Just Practicality

When all of its Android competition in 2013 uses quad-core processors, the cynic is us wonders how much of the decision to go Octa-core was influenced by Samsung’s marketing department. If you were an average Joe phone buyer, offered the “four-core” Sony Xperia Z or the “eight-core” Samsung Galaxy S4, wouldn’t you be tempted by the sound of the latter? Early benchmarks show that it’s not really all that much faster than the quad-core HTC One.

We’ll wait to see what sort of battery power effects the Exynos 5 provides before criticising the Samsung Galaxy S4’s processor any further. Without any power management modes engaged, we found that the HTC One and Sony Xperia Z barely last longer than a day – perhaps a more dynamic CPU is just what high-end mobiles need.


March 15, 2013, 1:11 pm

They could market this as Dual Quad-Core CPU, one quad for raw power and the other for power saving. That's closer to what it actually works like. But talking about 8 cores works better when you want to sell it. And then there are people who troll 8 cores as being too many cores, unused by apps and OS, as if all the 8 cores were supposed to be working at the same time...


March 15, 2013, 4:38 pm

I do wonder if this was more for marketing than anything else. CPU's already save battery when there not been driven, the only issue is that there will still be idle at the core CPU frequency. Dropping the core frequency will of course save battery, but the biggest battery saver is dropping the load on the CPU in the first place.

Anyone who's over clocked a PC, will know what I mean. eg. An over-clocked PC running at Idle, takes very little more power than a none over-clocked PC at idle, and this is usually only because your increasing the voltage.

There is of course the number of transistors for the different CPU family that will have an effect on power draw, but again how much difference this makes again at Idle I assume won't be that great.

When you take into account there has of course to be some sort of management of CPU load balancing, in itself taking CPU resources, and there the Startup/Shutdown of cores etc etc. I've a gut feeling the saving's might not be that great. And for the best saving's the OS needs to handle the affinity, so I assume for this to really have an effect Google will need to update the OS too.

Fingers crossed I'm totally wrong!!, as it would be very nice if what Samsung have done does work.

mister singh

March 15, 2013, 9:22 pm

Qualcomm S4 Pro overclocked at 1.8-1.9 Ghz in Sony Xperia Z scores 23k in AnTuTu and 9.5k in quadrant just shy of the Snapdragon 600.


October 29, 2013, 8:09 am

Exynos 5 Octa-core at 1.4 ghz underclocked and undervolted in Samsung Galaxy SIV, scored 27.2k in AnTuTu and 14.1k in Quadrant. Blazing fast!

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