The new Xserve has one or 2 1.33GHz G4 CPUs and uses DDR333 RAM for faster access. It also contains the new Firewire-800 announced only one month ago at MacWorld San Francisco.
The Xserve RAID packs an astonishing 2.52TB (that's ~2,520GB) of storage into 3U of rack space. The combination of size and price makes it a pretty compelling option for Macintosh servers.
The RAID box uses dual (independent, not redundant) intelligent RAID controllers that each control 7 ATA-100 drives, however the remaining bits (power supplies, fan assemblies) are entirely redundant.
Standard disk configurations are based on four or more 180GB ATA-100 drives with 8MB of cache. Controllers have 128MB of memory by default but can each be configured with up to 512MB.
As I had suspected when I saw the unit in a rack at MacWorld San Francisco, the RAID controllers can monitor external UPS units to figure out when they are likely to lose power. However, I didn't know that there are optional batteries that can keep the cache memory on the controller cards alive for 72 hrs.
If you have any interest in this kind of thing, check out the Management subpage. They've got some pretty sophisticated stuff in there, cute support for Rendezvous, and the ability to monitor (although it is unclear about maintaining) the system from any platform using a Java Applet.