Samsung Chromebook (XE303) Review: Testing ARM's Cortex A15
by Anand Lal Shimpi on October 31, 2012 9:00 AM ESTInside the new Chromebook
Similar to its predecessors, getting access to the internals of the new Chromebook doesn't require anything more than a tiny Phillips head screwdriver. There are four exposed screws and four more under the feet beneath the chassis. Remove all eight screws and you can pry off the bottom cover. The cover snaps into place so be careful if/when you remove it.
The new ARM based Chromebook
Inside the new Chromebook is a far more simplified setup. It honestly looks more like a modern day tablet under the hood. I never got the Celeron based Chromebook 550, but I do have the 500 which featured a dual-core Atom N570 processor. Here's a shot of that model for comparison:
The old Atom N570 based Chromebook
Right off the bat you'll notice a significant reduction in battery capacity. That old N570 based Chromebook had a mammoth 61Wh battery compared to the more tablet-sized 30Wh battery in the new model.
The old motherboard was also far less integrated. Discrete cards were used to provide cellular and WiFi connectivity, whereas the new board integrates WiFi (Marvell?) directly onto the motherboard.
The cost reduction extends to the SoC side as well. Intel charges $86 for an Atom N570, while the going rate for high-end ARM based SoCs is in the $20 - $30 range (and this is why ARM is the new AMD when it comes to keeping Intel pricing in check). I also suspect that this first run of Samsung Exynos 5 Dual chips are a bit leakier and perhaps even lower yielding than what we'll eventually see down the road. Samsung could be motivated to move these parts at a better cost structure as they work out kinks in manufacturing.
The 2-chip Atom solution
Note that the previous Atom solution required two chips: the N570 and its NM10 Express PCH. The N570 had a 2.1W TDP and was used for all IO, while the N570 and its two Atom cores needed about 8.5W. The combination was fine for a notebook but when Haswell can deliver much better performance within the same TDP, it's clear the old 45nm CPU + chipset were getting long in the tooth.
The far simplified, single-chip Samsung Exynos 5 Dual solution
Despite the absence of any significant heatsink, to remove 10.6W of heat you do need forced air convection hence the inclusion of a fan in the old Chromebook 500. The thermal requirements of the Exynos 5 Dual are significantly lower. The SoC benefits from Samsung's 32nm HK+MG LP process and is highly integrated, meaning there's only a single chip. Although there's a big heatspreader plate complete with heatpipe that runs over the Exynos 5, there's no fan needed. Removing the fan lowers build cost, reduces internal complexity, and helped Samsung shrink the chassis size.
There are a total of 8 x 256MB DDR3L devices (2GB total) that surround the Exynos 5 Dual SoC (4 on each side of the PCB). Each device is 8-bits wide, all connecting up to the 64-bit wide DDR3L memory controller. The DRAM is clocked at a 1600MHz data rate, resulting in 12.8GB/s of memory bandwidth to the chip. The Exynos 5 Dual integrates two ARM Cortex A15 CPU cores as well as an ARM Mali-T604 GPU.
The other big change on the motherboard is the move from a SanDisk discrete controller + NAND device to an integrated iNAND solution for storage. Capacity remains unchanged at 16GB, but the integrated eMMC controller does offer board (and perhaps cost) savings.
Moving to a lower power SoC not only gave Samsung some flexiblity in cooling, it also allowed it to run the platform with a much smaller battery. While the old Chromebook 500 used a massive 61Wh battery, the new model only needs a 30Wh unit. Battery life has gone down (Exynos 5 Dual isn't 2x more power efficient than the 45nm Atom N570) but so has weight as well. I believe the Chromebook 550 ditched the giant battery and moved to a ~40Wh unit, so the difference isn't as drastic there.
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Krysto - Thursday, November 1, 2012 - link
Tablets and phones don't boot-up instantaneously. That's waking from idle mode that you're talking about, which basically just means turning on the screen.Krysto - Wednesday, October 31, 2012 - link
When Cortex A7 arrives in big.Little I expect the idle times to drop dramatically in A15 set-ups, and I doubt Intel can keep up with that. Not to mention they still won't keep up in graphics department.Anand, can you stop plugging Surface into Android and Chromebook reviews? Why would I want to hear how Surface might do in the future with this chip that Chromebook already has? Seriously.
Exophase - Wednesday, October 31, 2012 - link
Anand's Cortex-A15 diagram looks really weird vs an official one.. http://regmedia.co.uk/2011/10/20/arm_a15_pipeline_...Three instructions are decoded and dispatched to 5 clusters of 8 execution queues (8 slots each) per cycle, then each cycle each execution queue can issue a cycle to its associated execution unit (note this diagram is using issue/dispatch opposite from how it's often used). There's no execution relationship like given in Anand's diagram, the clusters are: NEON (2x), load/store (2x), simple ALU (2x), multiply, and branch.
Anand Lal Shimpi - Wednesday, October 31, 2012 - link
I based my diagram on a lot of the content in here:http://www.arm.com/files/pdf/AT-Exploring_the_Desi...
Slide 20 introduces the independent issue queues, although subsequent slides make it all a bit more ambiguous (and more like the block diagram you included). I didn't include "issue" width for each of the arrows in my diagram to keep thing simple but I can see that it can definitely give the wrong impression.
Let me see about doing a better pass on the A15 once I'm back from my current trip.
Take care,
Anand
madmilk - Wednesday, October 31, 2012 - link
More proof that ARM ISA isn't magically more efficient than x86 in perf/watt.My i7-3720QM Mac can complete Kraken in 2100ms, with a load power consumption of 30W and idle power of 12W (display on at mid-brightness, discrete GPU off). Ivy has very good power gating, so I'll just assume the CPU is consuming 20W. This results in 42 Joules to complete one run of Kraken. The A15 on the other hand, with a differential of 4 watts (again assuming perfect gating at idle) takes 38.8 Joules. In server usage, perf/watt is king. If the best ARM can deliver is 10% better perf/watt at the expense of 5x per-core performance, they're not going to make a dent against Xeon. I imagine V8 could be optimized more for ARM, but the gains there are not nearly as big as before.
Some other observations -
I ran 8 instances of Kraken at once to make use of all the cores and HT, while reducing the effect of perf/watt-killing Turbo Boost. Power consumption was about 65W total, or approximately 55W going into the CPU. Each Kraken finished in about 3700ms, so what we have is 55W*3.7s/8 = 25 joules per Kraken. Much better, but obviously an apples-to-oranges comparison against the A15 which should probably have two instances run on it for optimal efficiency.
Also, shame on Intel/Samsung/Google for the Chromebook 500. 12W idling for a netbook is just ridiculous.
I don't think we can pull the 32nm vs 22nm fab card here either, because Intel has always been ahead in this respect and the gap is widening.
lemonadesoda - Wednesday, October 31, 2012 - link
The new chromebook is a near-winner! While it is targetting impulse purchase, low-budget buyers, and 2nd world economies, they should consider a 1st world premium buyer audience. If this had a better quality screen with "retina" pixel density, I would buy one in a heartbeat. I don't want to game... I want to read my PDFs without having to zoom to make the text legible... and with the SD card reader... it would be a perfect image display device for the SD cards once it comes out of the camera. 1366x768 is very 2009, not 2012.ol1bit - Wednesday, October 31, 2012 - link
I don't understand why Chrome OS continues at all?Just slapping JellyBean on this hardware would have much more functionality.
andrewaggb - Wednesday, October 31, 2012 - link
Only google can answer this question....Kinda like Firefox OS... or whatever they are calling it. Just not sure what the point is. Maybe they figured linux needs just a few more radically different distributions :-)
ssddaydream - Wednesday, October 31, 2012 - link
Please, will somebody ban this clown?ShaneMickey, that is...
ssddaydream - Thursday, November 1, 2012 - link
...there will be support that would allow AndroidOS, Linux, or Windows RT to be installed and properly functioning on this device.