How to turn on Incremental Compiling

I get these messages that Incremental Compiling is turned off but I don’t see any way to turn it on. I checked preferences and the build settings. I also searched the forum and the online user guide - and saw references to it but zero instructions. Any clues?

It’s automatic in 32-bit and not enabled for 64-bit yet.

If you are using a keyboard shortcut to run, make sure you release the keys immediately.

Out of curiosity, may I ask why? What happens if the keys aren’t released immediately?

You may ask, but…

But seriously. I think you’ll find that holding it down too long actually disables incremental compilation.

Version # ?

I hit Command R super fast and it still goes through all 197 modules.

you Didn’t say, is this 32-bit or 64-bit?

It was in 64 bit mode, but when I changed to 32 I got some complaints from the Apple OS but the compilation is faster. Not sure if the behavior is the same in 64 and 32 bit modes.

Incremental compilation doesn’t work in 64-bit yet.