Input and Output




  • Tap, Pinch, Rotation, Swipe, Pan, Long Press
  • Gesture recognizers are built-in for some UI elements, like UIButton and UIScrollView.


  • Can use more than one input point
  • The maximum number of simultaneous touches on iPhone is 5. On iPad, it's 11.



  • Built-in on all iPhones and newer iPods and iPads.
  • Older iPods and iPads require an external microphone attachment.



  • Built-in on all iPhones and newer iPods and iPads.
  • Includes both still image and video capture.
  • Newer devices have a front and back facing camera.
    • Back camera has better resolution than the front camera.
    • Back camera has a flash on iPhone 4 and iPhone 4S.



  • Determined using a combination of information from cellular, Wi-Fi, and GPS networks.
  • Cellular and GPS data is only available on devices with cellular chips (iPhones and iPads with 3G option).
  • GPS accuracy depends on being in a clear line of sight to GPS satellites, i.e. outside with clear skies and no tall buildings around.
  • At best, accuracy will be within 5 meters.

Heading (Direction)

  • Determined using a three-axis gyroscope.


  • Determined using an accelerometer.
  • Commonly used to rotate the visible view so that it's right-side up.


  • Determined using an IR sensor located near the earpiece.
  • Only returns a Boolean flag indicating whether the sensor is close to the user or not.



Screen resolution varies depending on device and model.

Device Model Resolution DPI (ppi) Ratio
iPhone 3GS 320 x 480 163 3:2
4 640 x 960 326 3:2
4S 640 x 960 326 3:2
iPod touch 640 x 960 326 3:2
iPad 2 1024 x 768 132 4:3
New 2048 x 1536 264 4:3

All latest devices have a Retina display. You'll notice that in the table above where some devices have 4 times the resolution of their older counterparts. In a nutshell, Retina means the pixels are so small that the human eye can't detect individual pixels. This makes text a lot clearer and images more vivid.

Selecting between Retina and non-Retina assets is done on-the-fly in iOS applications. In fact, no extra work is required on your part for text and built in UI components. As for external resources such as images, you need to provide two versions of the asset to the application.

  • Both versions should have the same name and extension, but the Retina version should have the @2x suffix added to its name. For example TitleImage.png and TitleImage@2x.png.
  • The Retina version should be double the width and double the height of the regular version. In order not to lose quality, you should work in the highest resolution then downscale your asset by 50% for the regular version.
  • When referencing assets in Xcode and Interface Builder, use the regular versions of the resources.


  • Audio output through the built-in speakers or headphones
  • Vibration can also be triggered, although it should be used sparingly as it is somewhat intrusive and can drain battery life.

  1. Compare iPad Models. Apple Inc., Visited Sep 11 2012.

  2. Compare iPhone Models. Apple Inc., Visited Sep 11 2012.

  3. iPod touch Tech Specs. Apple Inc., Visited Sep 11 2012.

  4. iOS5: Understanding Location Services. Apple Inc., Sep 4 2012.

  5. Matt Gemmell. iPad Multi-Touch., May 9 2010.

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