Learning Objective-C 2.0: A Hands-On Guide to Objective-C for Mac and iOS Developers

C. 32- and 64-Bit

For the past several years, Apple has been moving into 64-bit computing. Mac OS X Tiger (v 10.4) can run 64-bit command line programs, Mac OS X Leopard (v 10.5) can run GUI-based (AppKit) 64-bit programs, and Mac OS X Snow Leopard (v 10.6) can both run GUI-based 64-bit programs and boot a 64-bit kernel on some recent Macs.

Note

The earliest Intel Macs (those with Core Duo or Core Solo processors) are 32-bit only. iOS devices are also 32-bit only.

“32-bit” and “64-bit” refer to number of bits used to address memory. A 32-bit program uses pointers that are 4 bytes wide and can address 2³² or about 4 gigabytes (GB) of memory. A 64-bit program can theoretically address 2⁶⁴, or about 1.8 × 10¹⁹ bytes of memory. In practice, current ...