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Real-World Performance And Battery Life

Apple's iPad 2 Review: Tom's Goes Down The Tablet Rabbit Hole

Real-World Benchmarks

Early on we discovered how difficult it is to benchmark tablets.

Apple iPad: Input Lag Benchmark

Benchmarking responsiveness with a camera is the fastest approach. Of course, normal cameras won't cut it, since they only shoot at 29 FPS. That's unacceptable if you're trying to measure precise time differences. Going the stop-watch route is no better due to human-introduced errors. That's why I'm using a 1000 FPS high-speed camera to measure performance. Since, 1 frame = 1 millisecond, it’s possible to measure timings with a high degree of accuracy.

Tom's Hardware's Real-World Benchmarks
High Speed Camera
Startup Time
(Cold Boot)
Input Lag
Launch Safari
31.359 sec
290 millisec
717 millisec
iPad 2
25.977 sec
235 millisec
676 millisec

Input lag is time it takes from pressing a key to the time it takes for it to appear as text on the screen. This tells you how fast the iPad is registering an action. Ideally you want low input lag so that you don't feel the tablet stuttering as you type or click on buttons.

Apple's original iPad has an input lag close to 300 milliseconds, which is noticeable if you have a tendency to type fast. According to research published by Clemson University, the average college student has a reaction time of 200 milliseconds to visual stimuli. The difference between 290 and 200 milliseconds is what you can actually "feel." If you type quickly, consider a 90 millisecond delay adding up per keystroke. Just Google "input lag iPad," and you'll see the how much of a pain this can be.

The iPad 2 has a more favorable result of 235 milliseconds, which means that input lag is nearly unnoticeable.

Battery Life

Testing a tablet’s battery life tends to be highly variable unless you control the entire experience from beginning to end. Cumulatively, touch gestures don’t have a great impact on battery life. The biggest factors are CPU/GPU processing, screen brightness, volume, and WiFi use. In order to accurately measure battery life, I coded a script that automatically plays MP3s at 50% volume while browsing different Wikipedia pages every 12 minutes. This benchmark is probably overkill, but it gives you an idea of a worse-case scenario.

Battery Life
Maximum Brightness, Dynamic Brightness Disabled, 50% Volume
WiFi + MP3
WiFi Off
H.264 Playback
iPad 2

Based on the iFixit iPad 2 teardown, Apple's using the same battery in the iPad 2, so the improved battery life has more to do with efficient hardware.

Recharge Time

Recharge Time
AC Adapter
to 90%
to 100%
iPad 2

Charging times are a double-edged sword. Ideally, you want a nice slow charge so that your battery lasts more than a few hundred cycles. Fast charge times keep you away from the wall socket longer, but in the long run they also cut down on the battery's health. Usually, the rate of charge starts to slow down somewhere in the 80% to 95% region, which is why the charging time from 0% to 10% is faster than 90% to 100%. This is where the iPad 2 shows its strength. It gets to 90% faster, but it eases up on the charging current above 90% to keep the battery healthy.

Recharge Time
USB Adapter
to 90%
to 100%
iPad 2

If you're charging an iPad through a computer's USB port, expect to wait about 7 to 8 hours for a full charge.

Wireless Performance

It's wrong to look only at throughput to get a sense of network speed. Yes, the iPad 2 does slightly worse in throughput, but there are other factors that affect wireless performance.  Latency, processing time, and the type of data being sent also effect the perceived "fastness" of a network connection.

Think of a phone call. Throughput is the audio quality. Latency is the amount of time from when you speak into the phone until the person on the other side hears you. And processing time is your brain mulling what the conversation itself. If we apply this to networking, throughput is the amount of data you can send over time, latency is the lag due to data transmission, while processing time is the overhead incurred by receiving the data.

Now consider that latency plus processing time equals response time. This is where the iPad 2 holds a clear advantage. Apple didn't change the 802.11a/b/g WiFi + Bluetooth 2.1 controller (Broadcom's BCM4329), but the A5's horsepower is significant enough that it reduces latency and processing time. So even if the throughput isn't great, the iPad 2 holds a commanding lead in response time that helps it load Web pages and download emails faster over WiFi.

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