Every time Apple revises its Unix-based operating system, it produces a list of dozens and dozens of enhancements -- more than any ordinary human wants to read through -- and some of them so minor they're barely worth mentioning.

In their marketing, Apple wants to emphasize just a handful of features, some of them to tweak Microsoft for not offering them or having already deleted them from Longhorn's list of upgrades. Others are just plain cool, demo well, and might appeal to existing users who need some encouragement to part with their money for an upgrade.

Mac OS X 10.4 Tiger, numbered and named in Apple's peculiar fashion, ships tomorrow worldwide for $129 for existing and new Mac OS X users alike. A five-computer license for a household is $199.

Tiger can be installed on any G3, G4, or G5 Macintosh with a built-in FireWire port—FireWire cards don't count. Apple recommends 256 MB of RAM and 3 GB of free hard disk space. XPostFacto might get older and non-compliant machines to handle Tiger as it has for earlier releases.

Reviewing an operating system is always a tricky task: either you already like the general approach and are considering upgrading to a new version, or you have an aversion (rarely disinterest) in the OS and want ammunition.

Let me try to avoid both paths by focusing on what's new in Tiger. If you haven't used Mac OS X before, you should look elsewhere for an article that covers its general approach. Suffice it to say here it is the BSD flavor of Unix with tons of open source and free software under the hood and a pretty and usable interface on top.

Tiger has much that's familiar in it: the overall interface, structure, and underlying components are the same. That makes it even harder to review as it's fundamentally the same OS as Panther, but also fundamentally improved with changes from the kernel up to the tip-top interface level.

To put some sense behind looking at Tiger, I've taken a glance at some of the biggest additions that Apple has been marketing heavily and some of the subtler improvements behind the scene. Look through this addition, and see how they meet your own needs.

Tiger is evolution not revolution. Evolution isn't as exciting, but remember that a beak just a few millimeters longer might mean the difference between survival and extinction.

Video encoding. The H.264 video standard allows much higher and less pixilated levels of compression for exported and streaming video. In Tiger, this standard manifests itself in several places: in QuickTime, the underlying video software used in Mac OS X; in iChat AV 3.0; and in iMovie.

QuickTime will be able to play back much crisper and clearer streams from the Internet with less bandwidth. That's a big plus when Apple is fighting its battle for media player supremacy with Real and Microsoft.

In iChat AV 3.0, H.264 allows the fairly stunning sight of four simultaneous video chat participants who must also be running Tiger. Person-to-person video chat will works the same, although it can use less bandwidth and look better. But select two or three names in an iChat buddy list and you're launched into a multi-person chat.

iChat presents the other video participants in skewed frames with false perspective and a live reflection in a table top beneath their floating frames. This feature has a minimum cost of entry: The person initiating the conference must have at least a dual-1 GHz Power Mac G4 or any G5 and 384 Kbps of bandwidth in each direction.

Participants need at least a dual 800 GHz G4, a single 1 GHz G4, or any G5. (Here are the requirements.) iChat can now also handle 10-person audio chats with lower system requirements to initiate and participate.

This may be an improvement in collaboration for businesses that have remote offices and telecommuters and that might otherwise be relying on expensive or proprietary video solutions. I also know I'll be using this feature with my family as they upgrade to Tiger. Is it a killer feature? It's particularly interesting to see, but 10-person conference calls bypassing long distance charges may be less cool and more useful -- and save more money.

iMovie will be able to export in H.264, which should allow media creators to produce video that looks better under a much broader set of circumstances.