Yes, Johny, your Mac has a 64-bit CPU

I have written a lot of C++ code in the last year or so. The C family of languages have types that will vary in size depending on the OS and the CPU.

I thought my Macs had 32-bit CPUs because the “long” type uses 32 bits. Why would Intel sell 32-bit CPUs to Apple? I did not care for the answer.

However, my current work is very sensitive to the CPU word length. So I decided to look into the matter. Turns out that Apple is buying standard 64-bit processors from Intel. But somehow, the C compiler defaults to 32-bit binaries.

Thankfully, the fix is easy. Go from…

g++ -O2 -o test test.cpp

to…

g++ -O2 -m64 -o test test.cpp

For some code I wrote, this meant running twice as fast!

Disclaimers: 1) I have not checked whether the same thing is still true with MacOS 10.5. 2) You might encounter some difficulties if you try to link a 64-bit executable with 32-bit libraries. 3) I am not claiming that your software will run twice as fast with 64-bit words.