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CPU And GPU Performance: All About Graphics

Apple's iPad 3, Part 1: The Complete Retina Display And A5X Review
By , Alan Dang

The CPU: A9 Flavor

Apple A5X, Source: iFixitApple A5X, Source: iFixit

The iPad 3 features a new SoC, the A5X. Like the preceding A5, it features a dual-core A9 ARM processor clocked at 1 GHz. We've covered the architecture of the A9 in the past, so we won't revisit the details, but for those interested in a deeper discussion, you can head back to our original A5 coverage.


Apple A4 (iPad)
Apple A5 (iPad 2)
Apple A5X
Fab Node
45 nm
45 nm
45 nm
Processor
1 GHz ARM Cortex-A8 (single-core)
1 GHz ARM Cortex-A9 (dual-core)
Memory
256 MB LP-DDR
512 MB LP-DDR2
1 GB LP-DDR2
Graphics
PowerVR SGX535 (single-core)PowerVR SGX543MP2 (dual-core)PowerVR SGX543MP4 (quad-core)
L1 Cache
(Instruction/Data)
32 KB / 32 KB
32 KB / 32 KB
L2 Cache640 KB
1 MB


On paper, there's really nothing to suggest improved CPU performance from the A5X. There's no change in cache size, and though there's apparently twice as much on-die RAM, it has no impact on raw computational horsepower. The new A5X seems intended to help improve multitasking support and enable a beefier graphics engine, so our GeekBench results are, not surprisingly, largely unchanged.

GeekBench v2.2.7 Results
iPad 2
iPad 3
Dell Mini 1012
LePan II
Transformer Prime
CPU
Apple A5
Apple A5X
Atom N450
APQ8060
Tegra 3
Architecture
Dual-core A9
Dual-core A9
Single-Core Atom
Dual-core ScorpionQuad-core A9
Speed
1 GHz1 GHz1.66 GHz1.2 GHz1.4 GHz
Overall
764
760
917
649
1194
Integer
691
687
910
709
1781
Floating Point
921
920
762
943
1781
Memory
830
825
1105
362
1091


The GPU: Double Your Pleasure

One aspect of Apple's A5X truly shines: graphics performance. Since an ultra-high-resolution display is the iPad 3’s core selling point, Apple's A5X features a significantly more powerful graphics engine optimized for the Retina display. This increases gaming potential by a lot. In fact, Apple claims the iPad 3 offers double the graphics performance of the iPad 2. How is this possible?

GPU System-on-Chip
PowerVR SGX 535
(Apple A4)
PowerVR SGX 543
(Apple A5/A5X)
SIMD
USSE
USSE2
Pipelines
2
4
TMUs
2
2
Bus Width (in bits)
64
64
Triangle rate @ 200 MHz
14 MTriangles/s35 MTriangles/s


Apple still employs Imagination's PowerVR SGX543 architecture, used in the iPad 2. But whereas the iPad 2 was limited to a dual-core implementation (SGX543MP2), the iPad 3’s A5X sports a muscular quad-core GPU (SGX543MP4). Incidentally, Sony's PlayStation Vita also uses a the SGX543MP4.

Apple A5X, Source: UBMApple A5X, Source: UBM

That hardware change is easy to spot when you inspect the A5X's die. In the annotated layout above, you can quite clearly identify each of the four GPU cores. It also appears that RAM accesses has changed to accommodate the increased need for bandwidth. The A5 employed a pair of memory interfaces; UBM's image above suggests four on the A5X. To get a more illustrative story, though, let's look at GLBenchmark.

GLBenchmark 2.1.2
*native resolution
iPad 2
iPad 3
Kindle Fire
LePan II
Transformer Prime
GPU
PowerVR SGX543MP2
PowerVR SGX543MP4PowerVR
SGX540
Adreno 220
Tegra 3 (ULP GeForce)
Egypt Standard*
6661 frames (59 FPS)
6709 frames (59 FPS)
2847 frames (25 FPS)
3485 frames (31 FPS)
5388 frames (48 FPS)
Egypt Fixed Time Step*
47.598 s (59 FPS)
47.261 s (60 FPS)
116.138 s
112.659 s (25 FPS)
69.055 s (41 FPS)
Egypt Off Screen (720p)
10 146 frames (90 FPS)
15 663 frames (139 FPS)
2516 frames (22 FPS)
3603 frames (32 FPS)
6496 (58 FPS)
Pro Standard*
2962 frames (59 FPS)
2975 frames (60 FPS)
1981 frames (39 FPS)
2140 frames (43 FPS)
2726 frames (54 FPS)
Pro Fixed Time Step*
20.868 s (60 FPS)
20.857 s (60 FPS)
34.658 s
31.982 s (39 FPS)
24.189 s (52 FPS)
Pro Off Screen (720p)
7352 frames (147 FPS)
12546 frames (251 FPS)
2277 frames (46 FPS)
2332 frames (47 FPS)
3717 frames (74 FPS)


According to the standard tests in GLBenchmark, nearly identical scores on the iPad 2 and iPad 3 imply similar perceived overall gaming performance. That doesn't seem like it'd blow you away, but it's actually pretty amazing when you consider the iPad 3's 2048x1536 native resolution. Comparing these two devices at their native resolutions is by no means an apples-to-apples match-up. But it is cool that the iPad 3’s A5X delivers the same performance with four GPU cores at 2048x1536 resolution as the iPad 2’s A5 with two cores at 1024x768.

Comparing the raw graphics performance of each hardware implementation using GLBenchmark's off-screen tests reveals that the A5X delivers about 1.5-2x more performance than the A5. More interestingly, the Tegra 3-based Transformer Prime actually falls behind the older iPad 2. In fact, when we compare the Transformer Prime to the iPad 3, we see a two- to three-fold jump in performance favoring Apple's tablet.

GLBenchmark 2.1.2
iPad 2
iPad 3
Triangle Test
65.0 Mtriangles/sec
129.2 Mtriangles/sec
Triangle Texture Test
58.0 Mtriangles/sec
120.8 Mtriangles/sec
Triangle Texture Test, Vertex Lit
45.6 Mtriangles/sec
93.6 Mtriangles/sec
Triangle Texture Test, Fragment Lit
43.5 triangles/sec
92.3 Mtriangles/sec


According to Imagination, its PowerVR tile-based deferred rendering architecture is highly dependent on memory bandwidth, which means there's a direct relationship between throughput and triangle rates. Based on our results from the iPad 3, it's pretty clear that graphics performance improvements are related both to a more complex GPU and greater bandwidth. The iPad 2 and iPad 3 seemingly both employ 800 MT/s LP-DDR2 by way of a dual-channel configuration. However, the iPad 3 utilizes four 32-bit memory interfaces, which is two more than its predecessor.

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