iPhone Simulator Suddenly Started Running Very Slow

iOS Simulator games run very slow (low fps)

The Simulator is not a device. The Simulator uses the Mac's CPU (tons faster) and the Mac's memory (lots more). However the Simulator also emulates OpenGL ES via a software renderer, which is abysmally slow even on the fastest CPU.

Because of this and the fact that no end user will ever run an app on the Simulator, any performance measurements on the Simulator are utterly IRRELEVANT!

Sorry for shouting but I felt this needed to be said with conviction. ;)

iOs Simulator running slow

This is a very common bug with the simulator a way I get around it is.

IOS Simulator: Window > Scale > 50% - it makes the simulator look like an actual device and it fits your screen perfectly.

Then I just leave the simulator open at all times rather then closing after I'm done testing my apps. This saves Xcode having to load all the simulators files and directories each time you run your app.

Hope this helps, cheers.

Is the iPhone Simulator actually as slow as device itself

The simulator does a really lousy job of indicating app performance. In fact it doesn't try.

For most things the simulator is much, much faster than an iOS device. It runs your code on an x86 processor, which is much faster than the ARM and has many times more memory. (It also actually links again OXS frameworks, not iOS frameworks. There is glue code in the simulator that makes it work with iOS code, but it's not perfect.)

However, some things, like Core Image filters and OpenGL graphics, are actually slower on the simulator than on a real iOS device.

The bottom line is that you can't really tell ANYTHING about your app's performance from the simulator, and shouldn't try. You can do basic development on the sim, but when it comes time to test performance, use real devices, and make sure to test on the oldest/slowest device your app supports (usually an iPhone 4s or iPad 2).

You also can't test memory usage on the simulator. A program that will run out of memory and crash on an iOS device may run just fine on the simulator.

Xcode Simulator animations extremely slow when played in editor

If you press command+T it triggers the 'Slow animations' feature. I didn't noticed this setting until now. Doh!

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