旧的模拟器运行时可通过Xcode的首选项下载。

Older Simulator runtimes are available for download through Xcode's preferences.

转到Xcode - >首选项 - >下载以查看兼容的遗留模拟器运行时列表。

Goto Xcode -> Preferences -> Downloads to see the list of compatible legacy simulator runtimes.

El Capitan支持iOS 8.1和更新的运行时。

El Capitan supports iOS 8.1 and newer runtimes.

Yosemite支持iOS 7.1和更新的运行时。

Yosemite supports iOS 7.1 and newer runtimes.

有一个已知问题menti在Xcode发行说明中，它阻止iOS 7.1模拟器运行时在Xcode 7中工作。

There is a known issue mentioned in the Xcode release notes which prevents the iOS 7.1 simulator runtime from working in Xcode 7.

因此，您目前无法使用Xcode 7的iOS 7.1模拟器运行时。

Thus, you can't currently use the iOS 7.1 simulator runtime with Xcode 7.