Sun's homegrown operating system, Solaris, followed Darwin down the open-source path a few years ago, and since then, Apple's demonstrated some interest in adopting some of the code from that other Unix-ish OS. For example, Apple has already publicly announced that the performance tool dtrace will be borrowed from Solaris and make an appearance as Xray in the Xcode developer's tools when 10.5 is released.

It has been a poorly kept secret that Solaris's file system, ZFS, will be joining dtrace once 10.5 is released. ZFS has a number of features that would make it quite appealing for power users, such as the ability to take advantage of new disks as they are added to the system without having to rearrange partitions or destroy data. Our own John Siracusa also has pointed out that ZFS makes for a better fit than HFS in terms of adding slick features like Time Machine.

Still, all signs pointed to ZFS appearing as an optional file system in Leopard, much like UFS and case-sensitive HFS do now. After all, you don't make major changes like swapping the default file system without giving users some time to adjust. Or do you?

Sun's CEO, Jonathan Schwartz, seems to be saying that Apple does. In a presentation that was supposed to be all about the introduction of new RAID hardware by Sun, Schwartz dropped some words that are now being parsed as carefully as the Talmud. He indicated that ZFS, the file system that enabled Sun's hardware, would be named as "the" filesystem in Leopard at WWDC.

So, does "the" mean the primary system, or are we still back where we were prior to Schwartz pulling a premature specification, with ZFS being an option? There are a number of reasons to lean either way. In the anti column, ZFS would obviate the effort Apple put into getting Time Machine to work under HFS, and it would complicate data exchange for anyone who works in an environment that uses mixed versions of the MacOS. On the plus side, ZFS already handles metadata in a way that might allow Apple to shoehorn much of what they already use HFS for into the new file system. Suspiciously, a project to add case-insensitivity to ZFS has recently been fast-tracked by Sun.

The opinion here at Ars is that the disruption of a new file system and the late start ZFS had in Leopard (rumor had it that ZFS partitioning didn't even work in recent seeds) makes the probability of it becoming the default remote. At the same time, the added months between the planned WWDC seed and the public release at least makes the possibility plausible, if not likely.

Ars has contacted Sun to ask for clarification, but has not yet received a response. We hope to get ahold of Schwartz before Jobs does.

John Siracusa contributed to this article.