If you’re running the latest and greatest version of MacOS, High Sierra 10.13.4 — and you should be — then you’ll want to keep an eye out for a new notification that might pop up when you start an application. Simply put, Apple is going to start letting you know when an app isn’t based on 64-bit technology, which at some point in the relatively near future will mean that won’t run on your MacOS hardware.
Apple has been planning for a switch to full 64-bit compatibility for a while now. The reason is that all modern Macs are built around 64-bit processors, which bring some significant performance advantages. An app that’s written for 64-bit compatibility is going to have access to more memory and its going to produce much faster system performance overall. And the newest Apple technologies, like its Metal graphics acceleration capability that lets the CPU and GPU cooperate for faster graphics and gaming performance, only work with 64-bit apps.
For now, you’ll be able to continue running 32-bit apps without any bad consequences. The warning is therefore intended to help you prepare for the day that MacOS will only run 64-bit software. For now, that date remains some unknown time in the future, because Apple hasn’t yet determined when MacOS will make a complete transition to 64-bit-only.
However, if you open an app and receive the notification, you’ll want to contact the developer and ask them when they’ll have their app optimized for 64-bit compatibility. If they don’t plan to make the switch, then you’ll want to start thinking about alternatives.
The easiest way to find out which apps aren’t already 64-bit compatible is to ask MacOS itself. Simply open the Apple menu, select “About This Mac,” and then click on “System Report.” In the resulting report, scroll to “Software,” and then click on “Applications.” You can then select an app and check the “64-bit (Intel)” field, which will indicate “Yes” for 64-bit and “No” for 32-bit.
Again, you still have some time before your 32-bit apps will simply stop working. The sooner you start preparing for the switch, though, the easier the transition will be — whenever it occurs.