Alsoft has released DiskWarrior 4, the long-awaited upgrade to their essential disk-repair utility. DiskWarrior locates and repairs disk directory information, which can bring back to life an otherwise unusable partition which has no physical faults and no other data corruption. (DiskWarrior scored highly in David Shayer's "Shootout at the Disk Repair Corral" article, 2003-11-24, which compared major disk repair applications.) DiskWarrior 4 adds compatibility with Intel-based Macs, repairs file permissions, identifies corrupted preference files, and repairs Attribute B-trees and Access Control Lists under Mac OS X 10.4 Tiger. The utility requires Mac OS X 10.3.9 or later. DiskWarrior 4 costs $100; upgrades from previous versions cost $50, plus $9 for shipping the installation disc. (There is no downloadable version available for the upgrade.)