More CPU Horsepower Equals Better Experience
The iPhone 4S delivers better performance because it centers on the A5 system-on-chip, whereas the 4G uses the A4. Incidentally, earlier this year, Apple transitioned to the A5 on its iPad 2. So, if this seems like familiar ground, it really is. We already covered the architectural differences between the A4 and A5 in our iPad 2 review (Apple's iPad 2 Review: Tom's Goes Down The Tablet Rabbit Hole). So, if you want a refresher, feel free to check that story out. Today, our discussion is limited to performance.
| Apple | iPad | iPhone 4 | iPad 2 | iPhone 4S |
|---|---|---|---|---|
| SoC | A4 | A5 | ||
| Processor | 1 GHz ARM Cortex-A8 (single-core) | 800 MHz ARM Cortex-A8 (single-core) | 1 GHz ARM Cortex-A9 (dual-core) | 800 MHz ARM Cortex-A9 (dual-core) |
| Memory | 256 MB LP-DDR (single-channel) | 512 MB LP-DDR (single-channel | 512 MB LP-DDR2 (dual-channel) | |
| Graphics | PowerVR SGX535 (single-core) | PowerVR SGX545MP2 (dual-core) | ||
| L1 Cache(Instruction/Data) | 32 KB / 32 KB | 32 KB / 32 KB | ||
| L2 Cache | 640 KB | 1 MB |
Performance between the iPad 2 and iPhone 4S is not comparable though, because Apple underclocks the iPhone's A5 down from 1 GHz to 800 MHz. According to GeekBench v2, the iPhone 4S delivers about 60% more performance than its predecessor, but, as we'd expect, still falls shy of the iPad 2.
| Geekbench v2, Score in Points (Higher is Better) | iPad | iPhone 4 | iPad 2 | iPhone 4S |
|---|---|---|---|---|
| Overall | 456 | 383 | 746 | 624 |
| Integer | 365 | 294 | 681 | 562 |
| Floating-Point | 458 | 367 | 909 | 737 |
| Memory | 678 | 616 | 787 | 707 |
| Stream | 325 | 286 | 323 | 284 |
As it relates to real-world performance, this speed-up will manifest as faster boot-up and more responsive application launch times.
In the past, we've used a 1000 FPS high-speed camera in order to quantify the input lag you experience from typing on a virtual keyboard. This tells you how fast a smartphone registers an action. Ideally, you want low input lag so that you don't feel like the phone is stuttering as you type or click buttons. At a minimum, we're looking for input lag below 200 ms because that reflects the average reaction time of a college student to visual cues (though some competitive gamers can react within a 100 ms window).
It's common for actions to take 120-140 ms to register on the iPhone 4, according to our high-speed camera test. But, thanks to the A5, Apple's iPhone 4S offers around 50% less input lag, in the range of 80-90 ms. That's a notable improvement, especially for the folks who consider themselves to be seasoned texters.