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I'm quite sure that I read, in more than one place, that one of the features of iOS 5 was to be delta updates for apps. However, the massive download that was required for an update to Infinity Blade II (a great example of just the sort of app delta updates would be tremendously useful for) suggests to me that its update was done the old way, by a complete download of the entire new version of the app.

To make perfectly clear, I'm asking about when and if we can expect delta updates for iOS apps. Mac programs in the Mac App Store do not interest me. Another thing that might have confused reporting in the run-up to the release of iOS 5 is the fact that over the air updates for iOS itself are delta updates. Could it be that Apple never even promised delta updates for apps, and the press simply got these two things confused?

Edited to add: Since my original question wasn't clear, I'll try again. I know that right now, there are no iOS app delta updates. What I'm curious about:

  • Had Apple ever explicitly told developers or the press that they would be doable in iOS 5?
  • If so, does anyone know why it hasn't happened?
  • If not, has anyone heard if it's being worked on for the future?
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2 Answers

iOS 6 now supports delta app updates. This is awesome, and makes Real Racing 3 (a 1.1GB app) update in about 30 seconds instead of 20 minutes!

https://developer.apple.com/library/ios/#qa/qa1779/_index.html

Q: How can I reduce the downloaded size of my app update for users that already have the previous version installed?

A: Starting with iOS 6, the app store will automatically produce an update package for all new versions of apps submitted to the store. This package is optimized for updating an app from one version to another, and contains files that have changed between the prior version of an app and the new version of the app, excluding files that have not changed.

When used optimally, an update package is significantly smaller to download than the full package of the app and the update will install more quickly. Also, in many cases, this mechanism allows updates to large apps to be downloadable over cellular networks where app downloads are subject to a size limit.

In addition to new content, the update package contains instructions on how to transform the prior version of the app into the new version of the app. New files will be added, modified files will be replaced with their updated counterpart, and deleted files will be removed as part of this transformation. As far as the developer and user are concerned, this process is entirely transparent and the resulting updated app will be indistinguishable from a full download of the corresponding updated version of their app.

Further instructions for developers available at the link above.

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I believe you mixed the two.

iOS supports delta update, but only for the OS itself. iOS 5.0.1 was a ~40MB update.

Mac OS X supports delta update for the Mac App Store apps.

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OS X updates were not always deltas. The difference between combos and deltas are that the former allows for an update from any prior major release (e.g., 10.7.0 to 10.7.5), while the latter only allows for a single, minor revision (e.g., 10.7.0 to 10.7.1). OS X would deliver either a delta or a combo depending on your system's configuration. To say OS X updates were always delta is a bit misleading. –  cksum Dec 8 '11 at 16:26
    
You're right. I've removed that part. –  Loïc Wolff Dec 8 '11 at 16:39
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