Microsoft Knowledge Base Article 316304 contains the following summary:
This step-by-step article describes how to configure a stripe set with parity on a Windows NT Server 4.0-based computer. A stripe set with parity consists of equal-sized areas of free space on at least 3 disks and not more than 32 disks, which are combined into a single, fault-tolerant volume. When you configure a stripe set with parity, the computer can store a larger amount of data than it can if you use a single disk. You also experience faster read and write speeds when you configure a stripe set with parity instead of a single disk volume.