Apple is promising a fast turnaround for the next major release of OS X. Version 10.5, dubbed Leopard, should hit the streets in spring 2007. Beyond such front-end improvements as better search, chat, and application linking, a number of under-the-hood enhancements are of special note.

First and foremost, Leopard will be a 64-bit operating system and application platform through and through, from kernel to GUI. Depending on how thoroughly Apple exploits it, 64-bit operation may have a tremendous impact on graphics performance on the company's Core Microarchitecture systems, such as Mac Pro and Apple's new 64-bit iMac systems.

Apple's application frameworks, such as the Core Data database and Spotlight search, along with lower-level system services such as NFS, could also yield big rewards if Apple optimises specifically for 64-bit features of the CPU. No transient storage lies closer to the CPU than its registers, and 64-bit x86 applications have much more register space to play with. At present, OS X Tiger (10.4) has some 64-bitness about it at the system level, but it can't leverage much because Apple can't risk making software incompatible with 32-bit Macs.

Another low-level feature of Leopard is particularly good news for cross-platform developers: Apple is submitting Leopard to The Open Group for certification as a Unix operating system. OS X Tiger is Unix-based, just as is software from other certified commercial Unixes such as Solaris, AIX, and HP-UX. If Apple can pass The Open Group's certification tests, Apple not only gets to take "-based" out of OS X's classification but also has the potential to reduce to zero the number of changes needed to port Unix applications to OS X. Moreover, Apple has recommitted to its Darwin open-source project, so OS X's Unix foundation will continue to be open source.

The standout user-facing feature of Leopard is unquestionably Time Machine. This creates file system deltas, a record of changes to files and folders leading up to the present. Time Machine is similar to a file systemwide undo buffer, except that the user can select which specific changes to reverse. Rather than making checkpoints at fixed intervals, Time Machine works constantly in the background, recording deltas either to local storage or to a system running OS X Leopard Server. Leopard Server, which we'll cover in greater detail when Xserve ships, incorporates a Time Machine server that effectively maintains up-to-the-minute backups of clients' disk contents.