Each item is identified with a primary key, which can be either only the partition key if it can uniquely identify the item, or a combination of partition key and sort key. The partition key is also called a hash key and the sort key is also called a range key. Primary key attributes (partition and sort keys) can only be string, binary, or number. 

Initially, a single partition holds all table data. When a partition's limits are exceeded, new partitions are created and data is spread across them. Current limits are 10 GB storage, 3,000 RCU, and 1,000 WCU. Data belonging to one partition key is stored in the same partition; however, a single partition can have data for multiple partition keys. The partition key is used to locate the partition and the sort key is used to order items within that partition.