AMD A8-3850 Quad Core Desktop APU (updated July 10)

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AMD A8-3850 Quad Core Desktop APU

July 1, 2011 by Lawrence Lee

Product
AMD A8-3850
Socket FM1 APU
Manufacturer
Retail Price
~US$135

Earlier this year AMD launched their first set of Fusion processors, which joined CPU and GPU on the same chip, an APU (accelerated processing unit). It was the long anticipated union of AMD and ATI technology since the latter was acquired by the former in 2006. The new platform called Brazos consisted of a Bobcat CPU (a stripped-down low TDP version of previous AMD CPUs) and an entry level HD 6000 graphics chip, manufactured on a slightly smaller 40 nm process. The functions of the Northbridge were fused into the APU with the remainder bundled in the Southbridge in a new chip dubbed the Fusion Controller Hub (FCH). The new architecture became quite popular in the mobile space, for netbooks in particular. The design consolidation created substantial power savings making it competitive with Intel's Atom CPU, and the presence of a full-featured Radeon GPU put in the same league as Nvidia ION graphics.


The Llano desktop formula.

The next step for Fusion is the Llano platform, with its desktop chips dubbed Lynx. This time AMD has upped the ante, packing their newly minted desktop A6/A8 APUs with much beefier central and graphics processors manufactured using a 32 nm fabrication process (down from 45/40 nm). The CPU portion has four cores, built on the same K10 architecture as the Phenom II family. Driving graphics are modified Redwood chips (HD 5000 series cores) with the latest version of UVD and improved power gating to maximize energy efficiency. They also sport whopping 320/400 Radeon cores (AKA stream processors or shaders) compared to the 80 in the HD 6250/6310 chips found in Brazos APUs, so they've got some teeth and can do more than play HD video. Along with these upgrades comes a new socket, FM1, which with its 905 pins is incompatible with AM3 and AM3+.


Lynx quad core APU die shot.

On quad core versions of Lynx, the CPU takes up just over a half of the die, while the GPU occupies a significant portion on the other side. Due to space, cost, and energy constraints, L3 has been omitted. Each CPU core has its own dedicated 1MB of L2 cache, twice that of the Athlon II line. The die size is 228 mm² compared to 216 mm² for Sandy Bridge and and 256 mm² for Deneb (Phenom II).

AM3 vs. FM1 vs. 1155: US$100~$150 Comparison
Model
Speed
L2+L3
Cache
TDP
Features
Street Price
Phenom II X4 970 BE
3.5 GHz
2+6MB
125W
Unlocked
$150
Phenom II X4 965 BE
3.4 GHz
2+6MB
125W
Unlocked
$130
Phenom II X4 955 BE
3.2 GHz
2+6MB
125W
Unlocked
$115
Phenom II X4 840
3.2 GHz
2MB
95W
N/A
$100
Athlon II X4 645
3.1 GHz
2MB
95W
N/A
$105
Athlon II X4 640
3.0 GHz
2MB
95W
N/A
$110
Phenom II X2 565 BE
3.4 GHz
1+6MB
80W
Unlocked
$105
A8-3850
2.9 GHz
4MB
100W
HD 6550D
$135
A8-3800
2.4/2.7 GHz
4MB
65W
HD 6550D, TurboCore
?
A6-3650
2.6 GHz
4MB
100W
HD 6530D
$115
A6-3600
2.1/2.4 GHz
4MB
65W
HD 6530D, TurboCore
?
Core i3-2120
3.3 GHz
0.5+3MB
65W
HD 2000, HT
$140
Core i3-2105
3.1 GHz
0.5+3MB
65W
HD 3000, HT
$145
Core i3-2100
3.1 GHz
0.5+3MB
65W
HD 2000, HT
$120

We have one FM1 APU on our test bench, the top-end A8-3850 featuring a clock speed of 2.9 GHz and HD 6550D graphics with 400 Radeon cores. The other members of the family include the A8-3800 which is slower but supports AMD's TurboCore dynamic overclocking feature to make up some of the performance difference. The A6 use the 320 core HD 6550D GPU and are differentiated similarly. In the future, dual core A4 chips will be released as well as enthusiast models with unlocked multipliers.

The A8-3850 and A6-3650 debut at US$135 and US$115, respectively. According to AMD, the A8-3800 and A6-3600 will be priced similarly, though they declined to gives us concrete numbers. The CPU portion of the A8-3850 stacks up closely to the Athlon II X4 640, though the X4 840 is a better match as it has priced the 645/640 out of contention. Of Intel's Sandy Bridge processors, only the dual core models are in the same price range.

GPU Comparison
Model
HD
6570
HD
5570
HD 6550D
HD
5550
HD
6530D
Radeon Cores
480
400
400
320
320
Texture Units
24
20
20
16
16
Color ROPs
8
8
8
8
8
Clock Speed (MHz)
650
650
600
550
443
Effective Memory Speed (MHz)
1600 ~ 2000
1000 ~ 2000
1066 ~ 1866
800 ~ 1600
1066 ~ 1866
GPU Peak Compute (GFLOPs)
724
520
480
352
284

As for the HD 6550D, it has similar specifications to the HD 5570 with 400 Radeon cores, 20 texture units and 8 ROPs, with a slightly lower clock speed. The memory speed of the 5570 is 1000~2000 MHz depending on the type of memory used by the manufacturer while the 6550D's memory speed depends on what system RAM is used. Using faster RAM with lower timings typically produces little CPU performance improvement, but memory speed is critical for GPU performance. As the integrated memory controller on the APU services both the CPU and GPU, high speed DDR3 with low latencies is worth more than casual consideration.

A version of Hybrid CrossFireX is also included with the new APUs called Dual Graphics which allows one to combine the prowess of the IGP with a discrete GPU. In the past, this was not much help as the makeup and speed of previous IGPs limited the cards that could be used to entry level models. Dual graphics supports higher performing cards, the HD 6670, 6570 and 6450. Not only do these pairings provide a boost to 3D applications, but as some HD 6000 series cards can support three monitors, Dual Graphics will let you drive up to five displays simultaneously.



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