i OS 6.1.6 is the final release supported for the i Phone 3GS and i Pod Touch (4th generation). Apple announced i OS 7 on June 10, 2013 at its annual Apple Worldwide Developers Conference (WWDC) event, and it was released to the public on September 18, 2013 alongside the i Phone 5C and i Phone 5S.
With this release, Apple dropped support for the i Phone 3GS (due to hardware limitations) and the i Pod Touch (4th generation) (due to performance issues).
i OS 4 was the first major i OS release that reflected the name change.
Apple concurrently provides the same version of i OS for the comparable model of i Phone and i Pod Touch, usually devices released in the same calendar year.
It is also the first major i OS release that i Pod Touch users did not have to pay for.
The release of i OS 4.2.1 brought compatibility to the original i Pad and is the final supported release on the i Phone 3G and i Pod touch (2nd generation) due to major performance issues.
Therefore, i OS 5 was released for the i Phone 3GS onwards, i Pod Touch (3rd generation) onwards, and both i Pad, models.
The release of i OS 5.1 brought support for the i Pad (3rd generation).
i OS is a mobile operating system, developed by Apple Inc. Updates for i OS are released through the i Tunes software, and, since i OS 5, via over-the-air software updates.
With the announcement of i OS 5.0 on June 6, 2011, a USB connection to i Tunes was no longer needed to activate i OS devices; data synchronization can happen automatically and wirelessly through Apple's i Cloud service.
The other was i OS 4.2, replaced with 4.2.1 due to a Wi-Fi bug in 4.2 beta 3, causing Apple to release 2 golden masters (4.2 GM and 4.2.1 GM).