Apple Darwin User Manual download pdf (Page 11)

As a special exception, the System Preferences application provides a 32-bit fallback mode. If the user selects

a system preferences pane without a 64-bit slice, it relaunches itself as a 32-bit executable (after displaying a

dialog box). To maximize your users’ experience, however, you should still transition these preference panes

to 64-bit plug-ins as soon as possible.

Memory Requirements

A 64-bit app can consume significantly more memory than a 32-bit app. For this reason, it is tempting to

continue to ship 32-bit apps. However, this is usually not the right thing to do.

In OS X v10.6 and later, most built-in apps are 64-bit. The first time you run a 32-bit application, all of the 32-bit

framework slices must be loaded into memory. This means that loading older, 32-bit-only applications causes

significant memory pressure, particularly on computers with limited RAM. This often outweighs the additional

memory impact caused by larger data structures.

This concern is described in more detail in Performance Optimization (page 54), along with some tips for

improving your memory usage in a 64-bit environment.

Should You Recompile Your Software as a 64-Bit Executable?

Memory Requirements

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Apple Darwin User Manual Page 11