SQL Server 2005 introduces the concept of allocation units for data storage. Each partition (tables and indexes now consist of one or more partitions) has up to three allocation units (or IAM chains), depending on what features it uses. The first is for normal in-row data, which is essentially the same as any table in earlier versions. The next one is for LOB data, which is data stored in text, ntext or image columns, or the new large value types of course. The third is for storing row-overflow data. This is what we get when there are several varying size fields on a table that if they are filled up too much cause the total size of a row to exceed the ~8060 bytes that can fit in in-row data.